Greta Christina has a blog called Greta Christina's Blog (naturally). She posts lots of interesting stuff about atheism and other things. Today she strayed into science and posted a video about macroevolution (see below) [Macro-evolution" Vs. "Micro-evolution": More Video Fun]. Greta introduced it with ...
First, just so everyone's clear: "Macro-evolution" and "micro-evolution" are made-up words concocted by creationists to make themselves sound scientific. Biologists don't use them. They're scientifically meaningless. They're just different stages in the evolutionary process; "macro" is just "micro" over a longer period of time.
I posted this comment on her blog.
I'm afraid you have been mislead. Microevolution and macroevolution are perfectly good scientific terms and they are used by evolutionary biologists all the time.
There is legitimate scientific debate about whether macroevolution is more than just lots of microevolution or whether macroevolution encompasses mechanisms not seen in microevolution. It's the sufficiency of microevolution argument.
I happen to be one of those scientists who agree with Stephen Jay Gould that there are many levels of evolution (hierarchical theory). Thus, macroevolution cannot be sufficiently explained by lots of microevolution. There are other things going on at the higher levels [Macroevolution].
The video is very misleading because it assumes a simplistic version of macroevolution. There aren't any evolutionary biologists who believe in that kind of macroevolution. Thus, I have to conclude that the makers of the video are as ignorant of evolution as the creationists they mock.1
1The video was made by cdk007 who claims to have a Masters degree in Biology and a Ph.D. in Molecular Neuroscience.
The terms were coined by Iurii Filipchenko in 1927 and has been in use in evolutionary scientific discussions since.
Some examples that I grabbed from my reference manager:
Ayala, F.J. 1982. Microevolution and macroevolution. In Evolution from Molecules to Men (ed. D.S. Bendall), pp. 387-402. Cambridge University Press, Cambridge, UK.
Bock, W.J. 1972. Species interactions and macroevolution. Evolutionary Biology 5: 1-24.
Charlesworth, B., R. Lande, and M. Slatkin. 1982. A neo-Darwinian commentary on macroevolution. Evolution 36: 474-498.
Cracraft, J. 1982. A nonequilibrium theory for the rate-control of speciation and extinction and the origin of macroevolutionary patterns. Systematic Zoology 31: 348-365.
Cracraft, J. 1985. Species selection, macroevolutionary analysis, and the "hierarchical theory" of evolution. Systematic Zoology 34: 222-229.
Eldredge, N. 1982. La Macroévolution. La Recherche 13: 616-626.
Erwin, D.H. 2000. Macroevolution is more than repeated rounds of microevolution. Evolution & Development 2: 78-84.
Futuyma, D.J. 1989. Speciational trends and the role of species in macroevolution. American Naturalist 134: 318-321.
Gould, S.J. 1982. The meaning of punctuated equilibrium and its role in validating a hierarchical approach to macroevolution. In Perspectives on Evolution (ed. R. Milkman), pp. 83-104. Sinauer, Sunderland, MA.
Gould, S.J. 1982. Irrelevance, submission, and partnership: the changing role of palaeontology in Darwin's three centennials, and a modest proposal for macroevolution. In Evolution from Molecules to Men (ed. D.S. Bendall), pp. 347-366. Cambridge University Press, Cambridge, UK.
Gould, S.J. 1994. Tempo and mode in the macroevolutionary reconstruction of Darwinism. Proceedings of the National Academy of Sciences of the USA 91: 6764-6771.
Gould, S.J. 2002. Macroevolution. In Encyclopedia of Evolution, Vol. 1 (ed. M. Pagel), pp. E23-E28. Oxford University Press, Oxford, UK.
Grantham, T.A. 1995. Hierarchical approaches to macroevolution: recent work on species selection and the "effect hypothesis". Annual Review of Ecology and Systematics 26: 301-321.
Gregory, T.R. 2004. Macroevolution, hierarchy theory, and the C-value enigma. Paleobiology 30: 179-202.
Gregory, T.R. 2005. Macroevolution and the genome. In The Evolution of the Genome (ed. T.R. Gregory), pp. 679-729. Elsevier, San Diego.
Jablonski, D. 2000. Micro- and macroevolution: scale and hierarchy in evolutionary biology and paleobiology. Paleobiology 26 (Suppl.): 15-52.
Levinton, J.S. 1983. Stasis in progress: the empirical basis of macroevolution. Annual Review of Ecology and Systematics 14: 103-137.
Levinton, J.S., K. Bandel, B. Charlesworth, G. Müller, W. Nagl, B. Runnegar, R.K. Selander, S.C. Stearns, J.R.G. Turner, A.J. Urbanek, and J.W. Valentine. 1986. Organismic evolution: the interaction of microevolutionary and macroevolutionary processes. In Patterns and Processes in the History of Life (eds. D.M. Raup and D. Jablonski), pp. 167-182. Springer-Verlage, Berlin.
Lieberman, B.S., W.D. Allmon, and N. Eldredge. 1993. Levels of selection and macroevolutionary patterns in the turritellid gastropods. Paleobiology 19: 205-215.
Løvtrop, S. 1981. Macroevolution and punctuated equilibria. Systematic Zoology 30: 498-500.
Maurer, B.A., J.H. Brown, and R.D. Rusler. 1992. The micro and macro in body size evolution. Evolution 46: 939-953.
Mayr, E. 1982. Speciation and macroevolution. Evolution 36: 1119-1132.
McDonald, J.F. 1990. Macroevolution and retroviral elements. BioScience 40: 183-191.
McDonald, J.F. 1998. Transposable elements, gene silencing and macroevolution. Trends in Ecology and Evolution 13: 94-95.
Salthe, S.N. 1975. Problems of macroevolution (molecular evolution, phenotype definition, and canalization) as seen from a hierarchical viewpoint. American Zoologist 15: 295-314.
Stanley, S. 1979. Macroevolution. Freeman, San Francisco.
Stanley, S.M. 1982. Macroevolution and the fossil record. Evolution 36: 460-473.
Stanley, S.M. 1998. Macroevolution. Johns Hopkins University Press, Baltimore, MD.
Vrba, E.S. 1983. Macroevolutionary trends: new perspectives on the roles of adaptation and incidental effect. Science 221: 387-389.
Wright, S. 1982. The shifting balance theory and macroevolution. Annual Review of Genetics 16: 1-19.
I made the same mistake pretty early on when I jumped into the anti-creo wars. I heeded the advise of those who knew better than I and amended my arguments thusly, I trust that Greta will do the same.
Larry, in molecular terms how would you describe a macroevolutionary event? In my mind its something that involves a genetic bottleneck - a mass extinction leading to only a small number of genetically homogeneous survivors or a chromosomal alteration (such as the chromosome 2 fusion in human ancestors) - both of which will lead to a rapid alteration in the frequency of alleles in the population compared to the previous generation. Is this an incorrect way to think of it?
By the way don't be too hard on that videomaker, he isn't aiming at the scientific community. He is trying to reach the type of creationist that I have been arguing with on another site (here are this creationists 'killer' questions that 'evolutionists havent been able to answer' "1. If man evolved from the monkey like creature where did the monkey like creature come from?
2. Did a male and female monkey creature evolve simultaneously? (a) If yes what is the point of sexual organs? Why not just carry on evolving? (b) If no where did the female monkey creatures come from, or the women of today?
3. How long did these monkey like creatures live for?
4. If it took millions of years for us to evolve, to produce fully functional body systems. Then how on earth did the chain carry on, at what point did the monkey like creatures stop evolving and start re-producing?")
Larry, in molecular terms how would you describe a macroevolutionary event?
I don't think it's appropriate to think of macroevolution in molecular terms. That's the essence of the argument that macroevolution is decoupled from microevolution.
In my mind its something that involves a genetic bottleneck - a mass extinction leading to only a small number of genetically homogeneous survivors or a chromosomal alteration (such as the chromosome 2 fusion in human ancestors) - both of which will lead to a rapid alteration in the frequency of alleles in the population compared to the previous generation. Is this an incorrect way to think of it?
No, I don't think so. Both of the examples you give fall within the domain of microevolution.
Speciation by cladogenesis (splitting) is the beginning of a separation between microevolution and macroevolution. It's difficult to account for cladogenesis using standard population genetics. You need to take into account events that are outside of the evolving populations such as geography and climate. In a sense, macroevolution is about the interaction of evolving species with the environment over periods of million of years.
Species sorting, where two different species compete with one another and only one survives, is another classic example of a macroevolutionary event that cannot be explained by microevoution alone. It involves treating the species as the unit of selection but microevolution is only concerned with evolution within the species.
(N.B. I'm greatly simplifying species selection here in order to make the point that it differs from individual selection. Also, I'm personally not sure that species selection actually exists—that's part of the debate.)
It's difficult to account for cladogenesis using standard population genetics. You need to take into account events that are outside of the evolving populations such as geography and climate.
This distinction between micro and macro doesn't make much sense and I've said so before. Here are three examples: how would we account for them without considering no external factors? -antibiotic resistance -industrial melanism -the phylogeography of any European species
Evolution below the species level is NOT about looking at only the gene pool and ignoring external factors.
There is legitimate scientific debate about whether macroevolution is more than just lots of microevolution or whether macroevolution encompasses mechanisms not seen in microevolution.
Mechanisms other than drift and selection? Such as??
Speciation by cladogenesis (splitting) is the beginning of a separation between microevolution and macroevolution. It's difficult to account for cladogenesis using standard population genetics. You need to take into account events that are outside of the evolving populations such as geography and climate. In a sense, macroevolution is about the interaction of evolving species with the environment over periods of million of years.
Why is it difficult? Clearly we weren't there, and have difficulty reconstructing population genetics from that perspective. But how id the interaction of evolving species within the environment "over periods of millions of years" different from "over periods of tens or hundreds of years" except in the timescale?
It's all well and good to have separate terms to describe different timescales, but as a biologist myself, I've yet to hear of macroevolutionary mechanisms being discussed that are exclusive from microevolutionary.
As the YouTube video that you link to suggests, the mechanisms are the same (in that case, growth).
In the comments, cladogenesis is mentioned. Again, that's a large-scale description of a great many small-scale events. As you say, it is difficult to describe such an array of events, and so we create terms for large-scale events to simplify explanations of so-called macroevolution.
This distinction between micro and macro doesn't make much sense and I've said so before. Here are three examples: how would we account for them without considering no external factors? -antibiotic resistance -industrial melanism -the phylogeography of any European species
Evolution below the species level is NOT about looking at only the gene pool and ignoring external factors.
Point taken. It's not the distinction between whether external factors are important that counts.
The problem with microevolution is that it's very good at explaining evolution within a population but it fails as an explanation of how populations form in the first place.
Let's say you want to explain why there are four species of zebra. Can you do this using only microevolutionary phenomena?
Or let's say you want to explain why there are more marsupials in Australia than in Asia. Is there a microevolutionary explanation? Can someone who deals only with microevolution explain why there was a huge increase in the number of mammals about 65 million years ago?
It's all well and good to have separate terms to describe different timescales, but as a biologist myself, I've yet to hear of macroevolutionary mechanisms being discussed that are exclusive from microevolutionary.
Everyone (but you) seems to agree that species sorting is such a mechanism. Please tell me why you; (a) never heard of it, or (b) disagree that it's separate from microevolution.
In the comments, cladogenesis is mentioned. Again, that's a large-scale description of a great many small-scale events. As you say, it is difficult to describe such an array of events, and so we create terms for large-scale events to simplify explanations of so-called macroevolution.
What am I missing here?
You're missing the step where two distinct populations are created where there used to be only one. How do you explain bonobos and chimps using only population genetics?
The key to macroevolution is the mapping of standard evolutionary mechanisms to the real world over very long periods of time. Just knowing the standard microevolutionary mechanisms isn't sufficient to explain the large-scale changes.
Larry, Eldredge (1995) defines "species sorting" (also called "species selection) as "differential speciation or extinction of species within a larger group"; he clarifies that "Some lineages speciate at a higher rate than others, and some species are more prone to extinction than others" (119). These varying rates of speciation and extinction, according to Eldredge, produce definite patterns in the fossil record.
Now, to use the analogy contained within the YouTube video, all this entains is differential growth of competing branches that stem from the same trunk. It's still growth, albeit at a different scale at which new properties emerge.
At its most fundamental scale, however, these emergent properties still require microgrowth or speciation to be occurring. And as such, microgrowth and macrogrowth are NOT exclusive.
Also, Larry, you make my point for me: "The key to macroevolution is the mapping of standard evolutionary mechanisms to the real world over very long periods of time."
Then go on to contradict yourself in the very next sentence: "Just knowing the standard microevolutionary mechanisms isn't sufficient to explain the large-scale changes."
The creationists that will grant you microevolution but draw the line at macroevolution are not talking about Gouldian thought-experiments like species sorting. Some of them will even grant you speciation as long as it remains within a "kind."
From a scientific perspective, there is no need to invent any fundamentally different mechanism or process for macroevolution at any level, unless you believe reproductive isolation of populations to be such a process. Microevolution in the real world is always either about the interaction of genetics and environment (selection) or about random changes at the genetic level (in the case of drift).
Populations that become reproductively isolated (by any means, though I don't doubt that geographic isolation is the usual mechanism) are new populations whose gene pools are changed by drift and selection. If species-sorting processes are important, they occur because some populations survive and others go extinct due to classical population-genetic processes in changing (or not) environments. In the case of direct competition between related species, each is simply a part of the other's biotic environment, and as such can either be adapted to, or not.
Macroevolution is just the processes of microevolution, plus population fission. IMO.
Point taken. It's not the distinction between whether external factors are important that counts.
Thanks, but I'd have been more reassured if you hadn't used the "only population genetics" argument again in the very next comment! :o
Let's say you want to explain why there are four species of zebra. Can you do this using only microevolutionary phenomena?
1) Do you need macroevolution to explain the six or so subspecies of plains zebra?
2) How does macroevolution explain why there are four species of zebra? :)
You're missing the step where two distinct populations are created where there used to be only one. How do you explain bonobos and chimps using only population genetics?
How do I explain different populations of common chimpanzees using only population genetics? New populations can originate without speciation, you know :) Isn't it stretching macroevolution too far to say that it deals with the origin of populations?
At its most fundamental scale, however, these emergent properties still require microgrowth or speciation to be occurring. And as such, microgrowth and macrogrowth are NOT exclusive.
Everybody agrees that microevolutonary mechanism are important in macroevoluton. The question is whether they are sufficient.
How do I explain different populations of common chimpanzees using only population genetics? New populations can originate without speciation, you know :) Isn't it stretching macroevolution too far to say that it deals with the origin of populations?
I think you're avoiding the question.
How do you explain the formation of distinct populations within a species using only population genetics? What microevolutionary processes give rise to distinct populations?
No, I am making a point. You can't explain _anything_ about natural populations using "only population genetics" in the sense you mean, so I can't figure out why you imply that microevolution researchers are restricted to it.
But in fact, population genetics itself does not need to explain things without taking into account geography, climate and other external factors! See my three examples above.
What microevolutionary processes give rise to distinct populations?
Dispersal and vicariance.
Speaking of avoiding the question, is it your contention that every time there is more than one population, we are dealing with macroevolution?
Larry, Maybe I'm misunderstanding you on how you're defining microevolution, because you keep bringing up population genetics as a proxy. I'm referring to it as speciation, which, just as in your zebras and chimps analogies, regularly involves geographical and climatological factors that exceed the explanatory capacity of popgen. Or does it? - population genetics IS impacted by those and other environmental factors.
So I'm still struggling to understand how you see the species sorting of zebras, hominids, or other examples, outside of the microevolutionary modes of drift and selection. You mention species sorting - how is that different from a description of two popgen models where one population thrives and the other crashes (which could happen for various reasons compatible with microevolution)?
For instance, you ask: "How do you explain the formation of distinct populations within a species using only population genetics? What microevolutionary processes give rise to distinct populations?"
I'll give you two: (1) geographical isolation; and (2) diversifying selection.
Thus, I have to conclude that the makers of the video are as ignorant of evolution as the creationists they mock.
That seems hardly fair. The video in question isn't really discussing the possible distinction between micro- and macroevolution. (Call it framing if you must.)
cdk007 is the prolific author of such movies like The Evolution of the Flagellum (which IIRC is consistent with Nick Matzke's old Talk Origins flagellum essay with one or two errors), and the recently popular Evolution IS a blind watchmaker which ingeniously shows how to build a 24 hour:minute:second time piece with a genetic algorithm.
In cdk007's consistent ending catch phrase: "Think about it."
What I can say is that this thing of competing species is not good when it comes to model biogeographic colonization and other ecological changes, where models of drift prove to be much more predictive than models of species competition.
Describing differential survival at any level as if a "selection" has happened is of very little help as far as science goes. Remember, selection is just slection. The mechanisms that generate variation will still require other forms of explanation.
How can species competition produce any evolution? If one species wipes out another, that is a consequence, not a cause, of any "advantage" it may have had under a given circumstance. Selectionism at all levels frequently misleads into this teleological-like thinking.
Evolovability, for sintance. I doubt very much than anyone can present any evidence that the average "evolvability" of species has increased along the biological history of earth. MY feeling is that evolovabilty can increase or decrease anytime. pecilaization and generalization, they both continue to occur, no matter how much "selection".
Sources like those listed by tr gregory give a clue that micro/macroevolution are not terms invented by Creationists. To those, I'd add "Evolution above the Species Level" by Bernhard Rensch (English translation published 1959) and Eldredge's "Macroevolutionary Dynamics" (1989).
I'd say it's but another case of Creationists using sciencey-sounding words to pretend that they're smart; they really don't understand what microevolution and macroevolution are.
I read Dr. Moran's linked essay/book chapter on Macroevolution, and I still don't get it. What, exactly, are these processes and patterns that can't be explained by selection and drift within populations, together with the fission of populations due to (thanks windy) dispersal and vicariance? Species sorting? In hindsight we look back and see that some species/genera/families/orders etc. have flourished and radiated, others have not, and most have done OK for a while then disappeared. But if we had a time machine, we could go back and verify that all of these species, whether destined in the future to radiate or to go extinct, all consisted of populations, (metaphorically) dealing with the contingencies and vicissitudes of their biotic and abiotic environments with the genetic variance available to them; and that all those populations consisted of individuals that ended up having some finite number of surviving descendants. What's so different? Isn't microevolution the mechanism of macroevolutionary pattern? And if not, why not?
What, exactly, are these processes and patterns that can't be explained by selection and drift within populations, together with the fission of populations due to (thanks windy) dispersal and vicariance? Species sorting?
Yes. I think it's far to say that all knowledgeable evolutionary biologists admit that species sorting is a higher level process that can't be explained by evolution at the level of individuals within a population.
Group selection falls into the same category but it's not the same as species sorting.
I'd don't have the time, or desire, to explain species sorting. Read The Structure of Evolutionary Theory by Stephen Jay Gould.
"Read The Structure of Evolutionary Theory by Stephen Jay Gould."
Ah, the appeal to the Master. Right, I'll read that tonight and get back to you tomorrow.
But in the meantime, since you are disinclined to explain any of your knowledgable pronouncements from on high, let me give it a shot, and you can criticize, OK? That's how you like the dialogue to work here at the Sandwalk, it seems.
So. Species or clade sorting results from differential extinction and speciation among species considered as the unit of selection. Now, any post-hoc hindsight view of evolutionary history will certainly observe such differential extinction and speciation; some clades are still around, and quite diverse, others are barely hanging on, and many others are no more. But this special Gouldian species-sorting thing requires more than a post-hoc accounting of evolutionary successes and failures, it postulates that the pattern is due to something about the species involved--some intrinsic emergent property of the species level that operates above and apart from those boring ol' microevolutionary mechanisms.
Right? So my question is, like what? Species-intrinsic properties that I have seen referenced are things like "extinction propensity" and "speciation rate."
Am I being stupid? I just don't see how the likelihood of a species going extinct is anything but the likelihood of its component populations going extinct, and I know that populations go extinct when recruitment rates are lower than death rates--and it's individuals being born and dying.
You don't have to deign to explain it to me, but please just give me a hint so that if I do tackle the profuse verbiage of Gould's Brick, I'll have a search image in the jungle.
You don't have to deign to explain it to me, but please just give me a hint so that if I do tackle the profuse verbiage of Gould's Brick, I'll have a search image in the jungle.
You're not going to read up on species sorting, are you? You've already made up your mind.
I think it is fair to say that many, probably most, evolutionary biologists do not think there is any consitutively different mechanism for macroevolution than for microevolution, the one reflecting the accumulation of the other: macroevolutionary questions are made for comparisons across greater phylogenetic distances (and more remote common ancestors). As far as the debate over the units of selection, genes, organisms, and some hihger level social organization units (for instance, termite clone-nest) are acknowledged units of selection but not so species or clades. I guess what I want to clarify is that the actual importance of species selection is a controversial topic, up for discussion.
The argument in Gould's book actually unfolds across several chapters, so it is not very useful to tell someone to "read gould". I myself will concede that gould is right in pointing out to supra-individual units that have a clear biological reality: for instance, in eusocial insects. I freely agree that a greater, higher level unit has emerged that has allowed the evolution, for instance, of sterile workers. Gould however takes this as evidence of group selection. I don't. Systems theory is much more enlightening as to how these higher level units develop and evolve.
Gould himself recognized that the debates over levels of selection would probably never go away and even suggested that the controversies could be beyond the ability of the human brain to resolve. If that is not a warning, I dont know what is.
Larry, You're not going to read up on species sorting, are you? You've already made up your mind.
What is there for him to make his mind up about here? You're not even trying to explain anything.
For myself, I don't have the book by Gould handy to read up on, so I read the material that I could find from Eldredge on it, and quoted it here. Same response from you: nada.
What is there for him to make his mind up about here? You're not even trying to explain anything.
I'm not under any obligation to explain the concept of species sorting. What I object to is when people dismiss it without understanding it. That doesn't seem like a good way for scientists to behave.
The point about species sorting is that, properly understood, it is a higher level process where the survival of related species in a clade is dependent on emergent properties that belong to the species but not to any individual within the species.
It is generally understood that this would be a clear example of a macroevolutionary process that cannot be sufficiently explained by microevolution. The debate concerns whether there are any real-life examples of species sorting.
There are two reasons why I'm not trying.
(1) I'm not convinced that it exists and I don't want to be put in the position of having to defend something that I don't support.
(2) It's very complicated.
For myself, I don't have the book by Gould handy to read up on, so I read the material that I could find from Eldredge on it, and quoted it here. Same response from you: nada.
In the posting that I saw above you included speciation in our definition of microevolution. That's such an unusual definition of microevolution that I'm not sure we can have a meaningful discussion.
Gould himself recognized that the debates over levels of selection would probably never go away and even suggested that the controversies could be beyond the ability of the human brain to resolve. If that is not a warning, I dont know what is.
It's a warning not to make dogmatic statements like "macroevolution is nothing more than lots of microevolution."
The best you can say, if you're inclined to believe that, is, "there is considerable debate about the sufficiency of microevolution to explain macroevolution, I favor the side that says there are no higher level processes that distinguish macroevolution from microevolution and, furthermore, I favor a definition of macroevolution that is compatible with the idea that macroevoluton is no more than cumulative microevolution."
In his most recent book (The Ancestor's Tale) Richard Dawkins has adopted this position and I think it's quite admirable even though he uses self-serving definitions (p. 498).
I must mention the alleged distinction between macroevolution and microevolution. I say "alleged" because my own view is that macroevolution (evolution on the grand scale of millions of years) is simply what you get when microevolution (evolution of the scale of individual lifetimes) is allowed to go on for millions of years. The contrary view is that macroevolution is something qualitatively different from microevolution. Neither view is self-evidently silly.
You're right--I'm not going to go read Gould on species sorting very soon, but it's not because I've already made up my mind (it's because I have piles of exams and lab reports to grade--I am procrastinating on this as I type--and higher spare-time-reading priorities).
I agree with Dawkins on this point, at the moment, by virtue of Occam's Razor: I know microevolution happens and I see no reason to postulate additional mechanisms (other than population fission plus lots of time) to account plausibly for macroevolutionary patterns. The sticking point for me is that I have yet to hear a good example of an "emergent property that belongs to the species and not to the populations that make up that species." Microevolution itself is an emergent property at the population level, and I see nothing sepcial about a "species" that warrants granting it additional properties. I was fishing here for such an example, but nothing doing--it's a wade into the Gouldian swamp of over-writing or nothing. *shrug*
I'm not under any obligation to explain the concept of species sorting. What I object to is when people dismiss it without understanding it.
Which is why I am asking that you help me explain it. I won't speak for others here, but for myself I'm trying to understand it, and you're not helping. This is your blog - if you're not interested in discussing/explaining your viewpoints, why do you blog on them in the first place? You know full well that there is legitimate room for even knowledgeable biologists to question your claim that macroevolution includes mechanisms that are not merely emergent from microevolution, yet you began with an off-handed dismissal of those experts that disagree with you.
So don't give us bullshit that we're the ones who have not been behaving well for scientists.
You also say:
In the posting that I saw above you included speciation in our definition of microevolution. That's such an unusual definition of microevolution that I'm not sure we can have a meaningful discussion.
Then correct me. Don't be an ass. If you would re-read my initial comment here, you would see me asking "What am I missing here?" You said 'species sorting' in a manner that didn't illuminate much. And now you mention that you're not even sure that your justification for being an ass is correct?!
That said, the clarification that you offer Sanders makes a bit more sense. It had seemed to me that you were dismissing Greta's point just as dogmatically as that which you decry - I see that I stand corrected. Thank you for correcting me instead of being dismissive. For my part, I'm sorry if I appeared hypercritical - but it really does seem to me that it is as simple as micro + time = macro. That's skepticism for you.
I have nothing against species selection in principle. But that doesn't help clarify your "more than population genetics" definition. I'd like to know what the least common denominator of macroevolution is. Is everything involving more than one population macroevolution? Above, you even hint that group selection might be macroevolution? What the heck isn't macroevolution, then?
Should we conclude that since the Wahlund effect results by definition from the presence of more than one (sub)population, it's therefore macroevolution and unexplainable using population genetics?
"...results by definition...": sorry for the sloppy writing above, I meant of course that the definition requires it, not that substructuring will always lead to the W.E.
I don't agree that population genetics = microevolution. Microevoluton is more than that level of description. A clear connection to discussion of phenotypic changes must be made and contrasted with the actual biological and ecological facts. This includes an explicit history of environmental effects on the phenotype (which can do such interesting things like hiding genetic differences)
I consider microevolution to include evolutionary transitions that are well documented. I would include speciation; it is also within the domain of the study of microevolution; mechanisms like pre and postzygotic isolation, lesser and greater degrees of speciation can be observed in the field; many times it is a fairly recet event and therefore can be well-documented; For instance, the origin of new species of plants by alopoliploidy, or hybrid specis of insects. These mechanism os speciation can hardly be called "darwinian" and population is of little insight compared on what we can gain by simply studying the karyotipes. . So, microevolutionary studies of speciation are possible. And, microevolution is NOT equal to "population genetics" or " darwinian selection". Other evolutionary mechanisms are also going to be part of microevolution.
I read the essay. In fact, I just clicked on your link and read it again. I'm sorry to report that it didn't help to clarify my understanding of why the "sufficiency of microevolution hypothesis" ought to be discarded. After a fine treatment of the history of this controversy, there are simply assertions, by you and quoted from Gould and Eldredge, that microevolution is insufficient. But see, that's what I'm not getting--why is it insufficient?
That higher-level patterns are identifiable in hindsight does not require that new mechanisms are necessary. And statements like "Since speciation is not a direct consequence of changes in the frequencies of alleles in a population, it follows that microevolution is not sufficient to explain all of evolution." don't help--it's the premise I don't get. Why is speciation more than the simultaneous changes in allele frequencies in two populaitons that lead to reproductive isolation?
But you're right--you're under no obligation to explain or try to convince me. And likewise, I'm under no obligation to buy into your unexplained conclusions just because you've been thinking about it for 10 years.
I consider that microevolution usually refers to the differences that may evolve between closely related populations (or species; or within a population, such as sexual dimorphism) whereas macroevolution refers to the greater differences that we find as we compare sucessively more distant taxa ("body plans", for instance)
I wrote a long essay about Macroevoluton. It's clear to me that some of the critics on this blog haven't even bothered to read my essay.
Do you count me as one of these critics? I didn't find an answer to my population question there. You quote Ridley saying
Microevolution therefore refers to changes in gene frequency within a population .... Macroevolutionary events are more likely to take millions, probably tens of millions of years. Macroevolution refers to things like the trends in horse evolution described by Simpson, and occurring over tens of millions of years, or the origin of major groups, or mass extinctions, or the Cambrian explosion described by Conway Morris. Speciation is the traditional dividing line between micro- and macroevolution.
There is a world of evolution happening between one single population and macroevolutionary changes taking millions of years. Is the dividing line perhaps hidden behind those four dots?
I'm not trying to nit-pick, but I think the definitions offered in this thread are contradictory. Imagine a simple population which is divided in two by a geographic barrier. Is that macroevolution?
I like Larry's essay. There is indeed a historical context in which the neodarwinian dogmatism of population genetics would hinder any serious consideration of macroevolutionary patterns.
Macroevolutionary patterns are fascinating, for instance, punctuated equibilibrium. But I specially like the correspondence betwen geological change and speciation, For instance, the number of species of molluscs has raised cintinuously since the atlantic coasts of south america and africa have become available... and then we have the asteroids, and fluctuations in the composition of the atmosphere...
Whta I am trying to say ifs that this pattern is more accidental, drift like: THIS is what becomes apparent to me from macroevultionary analysis. It is NOT guided by some higher level (specis level) process of selection; but a process of DRIFT. Of available resourcs and accidents of colonization. As I already mentioned above, models of drift rather than competition among species are better predictors of the ecology that will develop in a colonization process. There is no such thing as "survival of the fittest" perfecting any new organic changes at the level of species selection.
I do not believe in species selection. Further, while study and description of microevolution and macroevolution can be very different, there is indeed a link: microevolutionary changes are conserved in a lineage, and are in efect the "steps" of the more long term, macroevolutionary pattern.
macroevolution is obviously a domain in itsefl at another scale that needs to follow up on ong-term geographicgeological changes too. It is not reducible to microevolution. Nevertheless, there has been much talk about macroevolution in terms of differente evolutionary mechanism, rater tahn a different level of bservation. Specially, some evo-devo people argue that microevolution is true for speciation an adaptation, but not a good explanation for the apparently non-adaptive difference in phyla body plans. The cambrian "explosion"would be the result of some kind evolutionary happenstance that somehow changed is argued to be outside the the kind of things that we can observe in microevolution. Thye argue, for instance, that this coud relate to the evolution of a very unique, archetypical gene regulation network (I don't buy it). How can a mechanism produce body plan differences without ot involving microevolution? What ARE these non-microevolutionary mechanisms that they may produce organic evolution? How?
I think the cambrian explosion, is much like a new shoreline for molluscs, or when vertebrates moved to dry land, or to flying. You will see an increase in the number of species, which has more to do with occupation of a previously unexplored lifestyle or resource, than with the violation of regular microevolutionary mechanisms.
Sanders and Sven, If it helps, I noticed (a bit belatedly, but still) that John Wilkins has an entry up on the TalkOrigins site on Macroevolution: It's definition, philosophy and history. It's a much better explanation of the controversies (surrounding disagreements over definitions) and reductionist arguments than Larry's, IMHO, which doesn't clarify definitions very well.
If it helps, I noticed (a bit belatedly, but still) that John Wilkins has an entry up on the TalkOrigins site on Macroevolution: It's definition, philosophy and history. It's a much better explanation of the controversies (surrounding disagreements over definitions) and reductionist arguments than Larry's, IMHO, which doesn't clarify definitions very well.
My essay was written as a rebuttal to John's. That's why I quote him at the start of my essay.
I'm sorry if you find my definitions of macroevolution difficult to understand. I tried to support them wherever possible with quotations from evolutionary biologists who actually study macroevolution. John gives you his version of macroevolution.
I think you still don't get one of the main problems. Those who study macroevolution think of it as a discipline that attempts to decipher the real history of life on Earth. This history includes things like ice ages and mass extinctions and how they affected life.
Saying that microevolution is all that's needed to understand macroevolution is like saying that relativity and quantum mechanics are sufficient to explain the formation of our particular solar system.
Larry, Yes, I'm aware that I'm not understanding everything you're saying - some of it comes off as counter-intuitive to me, and therefore difficult to grasp. That's why I started off asking for better explanations, to help understand your point of view (and I assumed that you had a valid point from the beginning, that I wasn't fully grasping). Instead I got off-handed dismissals and insults of being "sad" and "dogmatic." It made you sound arrogant and motivated only to shove your dogma to me from up on high.
That said, I'm sorry, I did skim over the intro to your essay and mention of Wilkins. As such I only stumbled on it later.
And I've been giving it some more thought in the past day, trying to understand both your and Allen's comments better (Allen I think agrees with you, and he has my utmost respect for his patience at explaining such things). Reference to the concept of cladogenesis alone didn't seem to me to be more than microevolution of divided populations, hence my skepticism. But Allen put it in contrast to anagenesis, reinforcing the line between micro and macro at speciation, and in the context of punctuated equilibrium. In other words - microevolution can be viewed as the change over time of one species, while macroevolution is change over time of more than one species. I imagine that's what you were getting at earlier. And that's a completely valid way of looking at it, I think, which completely supports your argument.
But placing emphasis on the term speciation (or at any other level of hierarchy) is just one perspective. As it's been noted, definitions of macroevo and microevo vary depending upon whether it's a geneticist or an ecologist doing the talking. Does that mean that one's right and the other is wrong? I seriously doubt that. But speciation IS an arbitrary term, because species are not fixed entities, and there is no mechanism of speciation outside of adaptive and non-adaptive modes of change, right? All of common descent follows from that.
So, from the perspective of mechanisms at the genetic level (viewing genes as evidence of common descent), then Wilkins position is completely valid in its own right. I just happen to share that viewpoint.
So when you say: "Saying that microevolution is all that's needed to understand macroevolution is like saying that relativity and quantum mechanics are sufficient to explain the formation of our particular solar system."
... I say that I agree completely, in terms of practical understanding. That's simply too much material for us to grasp without higher-order explanations. In theory, however, the formation of the Universe was propogated from such reductionist natural laws however, right?
It's all too much information for anyone to understand at all levels though, which is why we have different explanatory models for different hierarchical levels. I think.
Does that sound about right? (Either way, I really do appreciate the explanation, finally - as you said, these are NOT simple concepts)
When someone says that macroevolution is simply lots and lots of microevolution they are making a dogmatic statement that doesn't reflect the true science.
What they should be saying is ...
There is considerable controversy in the scientific community over the sufficiency of microevolution to explain macroevolution. By some definitions of macroevolution—those not used by most people who study macroevolution—it is possible to take the position that microevolution is sufficient to explain macrevolution provided that one rejects hierarchical theory. That's the position I take after having studied the controversy.
That's just a wee a bit of an overstatement though, don't you think? Now it sounds as though you're trying to marginalize the gene-centric viewpoint.
Not to mention, the last sentence, "That's the position I take after having studied the controversy." Sounds kinda egotistical to me, but again, I shouldn't be surprised at that given how this conversation has gone - how about just "That's the species-centric position"?
The analogy is fit. The solar system could have been different. But we would still understand it through the laws of physics. Without them, all we have is a description. We don't have a different physics for each solar system. macroevolution does ot violate microevolution; rather, without microevolutionary mechanisms, macroevolutionary patterns would not be possible: not the other way round.
I think the "macro" in macroevolution should refer to deep time and long phylogenetic distances. I think it is misleading to think of macroevolution as speciation or biogeoegraphic environmental changes, that can occur in quite small time scales and with great phylogenetic proximity. Cleary the notion of macroevolution is intended to describe long processes such as the origin of mammals, for instace. It's all bout scale, and not so much about specific hypotheses (particlarly so, species selection)
Larry, Also, you said: "When someone says that macroevolution is simply lots and lots of microevolution they are making a dogmatic statement that doesn't reflect the true science."
Since when is the genetic record, or phylogenetics, not true science? The genetic record is one of the most convincing evidences of macroevolution, and that there is no distinction between macroevolution and microevolution at the gene level. Genes don't know the difference between cladogenesis and anagenesis.
Since when is the genetic record, or phylogenetics, not true science? The genetic record is one of the most convincing evidences of macroevolution, and that there is no distinction between macroevolution and microevolution at the gene level. Genes don't know the difference between cladogenesis and anagenesis.
This is one of the ways in which it's so easy to go wrong.
The comparison of sequences is, indeed, one of the most powerful bits of evidence for evolution. It reveals that we all share a common ancestor and it provides enormously powerful support for the concept that evolution requires change in the frequencies of alleles in a population over time.
However, a comparison of the horse genome and the elephant genome tells us absolutely nothing about the actual history of the evolution of horses. You can't make those famous horse trees from the sequences of the survivors.
Furthermore, if you're interested in whether morphological change is associated with cladogensis or anagensis then staring at sequences isn't going to help. The patterns of macroevolutionary change, which form the basis of marcoevolutionary theory, just aren't accessible via sequences (with a few exceptions).
One of the most interesting problems in macroevolution is the Cambrian explosion. The sequences, for the most part, tell us that it never happened but the fossil record suggests otherwise.
As I say in my essay ...
If we could track a single lineage through time, say from a single-cell protist to Homo sapiens, then we would see a long series of mutations and fixations as each ancestral population evolved. It might look as though the entire history could be accounted for by microevolutionary processes. This is an illusion because the track of the single lineage ignores all of the branching and all of the other species that lived and died along the way. That track would not explain why Neanderthals became extinct and Cro-Magnon survived. It would not explain why modern humans arose in Africa. It would not tell us why placental mammals became more successful than the dinosaurs. It would not explain why humans don't have wings and can't breathe underwater. It doesn't tell us whether replaying the tape of life will automatically lead to humans. All of those things are part of the domain of macroevolution and microevolution isn't sufficient to help us understand them.
We have traces of burrows and Kimberella ( a mollusc, a derived protostome) from the precambrian. Plus molluscan spiral-cleaving patterns in fossil embryos. Hard parts also fossilize more easily than soft and small invertebrates, which helps explain the much greater record in the cambrian, when hard body parts and increased body sizes evolve.
I think there is no evident inconsistency between the molecular and fossil data. The main lineages of metazoans had already diverged before the cambrian "explosion".
Saying that microevolution is all that's needed to understand macroevolution is like saying that relativity and quantum mechanics are sufficient to explain the formation of our particular solar system.
Ah, but saying that we can't in practice reduce macroscale events is subtly different from the claim that "macroevolution is more than repeated rounds of microevolution". Would you say that solar system formation is something more than repeated rounds of quantum mechanics? Or relativity?
I think there is no evident inconsistency between the molecular and fossil data. The main lineages of metazoans had already diverged before the cambrian "explosion".
I don't disagree. Nevertheless, there seems to have been a remarkable change in morphology of a number of lineages in a short period of time. That's not something that's predictable from simply examining the sequences of present day species.
Furthermore, there were a number of lineages that went extinct by 500 million years ago. Those extinctions help inform us about evolution. For example, they give rise to Gould's hypothesis that diversity was greater in the past than today. You can't get that sort of data from sequences.
Ah, but saying that we can't in practice reduce macroscale events is subtly different from the claim that "macroevolution is more than repeated rounds of microevolution".
It's more complicated than that. What paleontologists are saying is that deciphering the history of life requires a lot more than just microevolution. What you're missing is the fact that macroevolution isn't defined the way you think it is.
In addition, there's the possibility of things like species sorting which really are uncoupled from microevolution.
If Eldredge & Gould are correct and punctuated equilibria are common patterns in evolution then even that is something that cannot be fully explained by microevolution. There's nothing in microevolution that predicts an association between visible evolution and cladogenesis.
Larry, I wasn't using genetics in terms of "comparative genetics" - I was referencing genetics as the fundamental unit of heredity. Whereas looking at evolution from the perspective of species and populations yields a discontinuous landscape, looking at evolution from the perspective of the heredity (and the units of it) yields a continuous landscape.
Perhaps I shouldn't use the word macroevolution to describe what I'm talking about though. I'm talking about descent and ancestry, more specifically. Literally speaking, we can theoretically trace our ancestry back to the common ancestors that reunite us with other species, phyla, even domains of life. That's not the way we process the data (how could we), but it's the theoretical conclusion. This interpretations seems to jibe with what you're saying - or at least the excerpt that you just quoted from your essay.
As you and Allen have been pointing out, my definitions of macroevolution and microevolution appear to be quite off the mark however. There is a history stemming from the modern synthesis that I'm not fully versed in, being a much younger student of science. And I'm not formally educated as an evolutionary biologist.
But given these definitions of macroevolution and microevolution, I think that the founders of the modern synthesis may have chosen their labels poorly. Intuitively, they conjure notions of continuity between "lots" and "little" change.
It's more complicated than that. What paleontologists are saying is that deciphering the history of life requires a lot more than just microevolution. What you're missing is the fact that macroevolution isn't defined the way you think it is.
How do you know? I haven't offered a definition, I have asked you to clarify your definition.
There's nothing in microevolution that predicts an association between visible evolution and cladogenesis.
The cambrian looks to me like the "typical" extinction-and-replacement pattern, stepping in after the ediacaran fauna, though I will grant that a different ecology originated (large predators).
I don't think the cambrian has specially high taxonomic diversity; in fact, the earth in general has less species diversity since dry land had not yet been invaded by groups such as the vertebrates, for instance. Remember, also, that species diversity is much greater on land than on sea. It is a fact that species diversity on aerth has increased since the cambrian
The only thing that we can argue si that more "phyla" were present in the cambrian. I would expect some cambrian lineages to go extinct, but I also believe we have a fair surviving sample of the main groups originated in that time. Many of the "bizarre" phyla argued by gould have been demonstrated to belong to known phyla; odontogriphus was a mollusc; amiskwia, a chaetognath; Hallucigenia, an onychophrona; the list continues. Further, many are not so bizarre that we may not recognize some affnity, such such as ecdysozoa, for instance. In summary: cambrian is not SOOO weird.
I think it is important to understand that the fact that we can account for a greter number of "phyla" than what survives nowadays does not mean that something particularly exceptionla was going on. YOu must corrct your phylogenetic scale. These are speciaition events like any other but becuase they happened very long ago, these twigs have become the basalmost branches when the later forms are included. For instcne, if you were to look in the triassic, you could surely say there were many ore "classes" of tetrapods then than now. THis is why it is important to correct the common misconception of invoking some "special mechanism" without considering this simple "phylogenetic scaling". This looks more to me like an ecological radiation of the bilateria, like that of many other groups that we may choose to observe in the fossil record.
Sanders, I wasn't invoking any special mechanism for the Cambrian explosion. I'm well aware of the distinction between phyla and their origins as speciation events. (So is Gould, BTW, in spite of the fact that some people think he's stupid.)
All I'm saying is that we wouldn't even be discussing these problems if all we had to look at were sequences. They are clearly macroevolutionary problems that have very little to do with microevolution.
I mereley wish to increase your awareness that some BS is being pushed under the banner of macroevolution. Many "grand men" of evo-devo believe that some unique mechanism happened in the cambrian allowing for "phylum-grade" differences (rather than mere "species-grade" differences, where "regular" micorevolutionary mechanisms would be at work).
I also happen to think that species selection is not very enlightning to understanding macroevolutionary patterns.
Greta Christina has a blog called Greta Christina's Blog (naturally). She posts lots of interesting stuff about atheism and other things. Today she strayed into science and posted a video about macroevolution (see below) [Macro-evolution" Vs. "Micro-evolution": More Video Fun]. Greta introduced it with ...
67 comments :
The terms were coined by Iurii Filipchenko in 1927 and has been in use in evolutionary scientific discussions since.
Some examples that I grabbed from my reference manager:
Ayala, F.J. 1982. Microevolution and macroevolution. In Evolution from Molecules to Men (ed. D.S. Bendall), pp. 387-402. Cambridge University Press, Cambridge, UK.
Bock, W.J. 1972. Species interactions and macroevolution. Evolutionary Biology 5: 1-24.
Charlesworth, B., R. Lande, and M.
Slatkin. 1982. A neo-Darwinian commentary on macroevolution. Evolution 36: 474-498.
Cracraft, J. 1982. A nonequilibrium theory for the rate-control of speciation and extinction and the origin of macroevolutionary patterns. Systematic Zoology 31: 348-365.
Cracraft, J. 1985. Species selection, macroevolutionary analysis, and the "hierarchical theory" of evolution. Systematic Zoology 34: 222-229.
Eldredge, N. 1982. La Macroévolution. La Recherche 13: 616-626.
Erwin, D.H. 2000. Macroevolution is more than repeated rounds of microevolution. Evolution & Development 2: 78-84.
Futuyma, D.J. 1989. Speciational trends and the role of species in macroevolution. American Naturalist 134: 318-321.
Gould, S.J. 1982. The meaning of punctuated equilibrium and its role in validating a hierarchical approach to macroevolution. In Perspectives on Evolution (ed. R. Milkman), pp. 83-104. Sinauer, Sunderland, MA.
Gould, S.J. 1982. Irrelevance, submission, and partnership: the changing role of palaeontology in Darwin's three centennials, and a modest proposal for macroevolution. In Evolution from Molecules to Men (ed. D.S. Bendall), pp. 347-366. Cambridge University Press, Cambridge, UK.
Gould, S.J. 1994. Tempo and mode in the macroevolutionary reconstruction of Darwinism. Proceedings of the National Academy of Sciences of the USA 91: 6764-6771.
Gould, S.J. 2002. Macroevolution. In Encyclopedia of Evolution, Vol. 1 (ed. M. Pagel), pp. E23-E28. Oxford University Press, Oxford, UK.
Grantham, T.A. 1995. Hierarchical approaches to macroevolution: recent work on species selection and the "effect hypothesis". Annual Review of Ecology and Systematics 26: 301-321.
Gregory, T.R. 2004. Macroevolution, hierarchy theory, and the C-value enigma. Paleobiology 30: 179-202.
Gregory, T.R. 2005. Macroevolution and the genome. In The Evolution of the Genome (ed. T.R. Gregory), pp. 679-729. Elsevier, San Diego.
Jablonski, D. 2000. Micro- and macroevolution: scale and hierarchy in evolutionary biology and paleobiology. Paleobiology 26 (Suppl.): 15-52.
Levinton, J.S. 1983. Stasis in progress: the empirical basis of macroevolution. Annual Review of Ecology and Systematics 14: 103-137.
Levinton, J.S., K. Bandel, B. Charlesworth, G. Müller, W. Nagl, B. Runnegar, R.K. Selander, S.C. Stearns, J.R.G. Turner, A.J. Urbanek, and J.W. Valentine. 1986. Organismic evolution: the interaction of microevolutionary and macroevolutionary processes. In Patterns and Processes in the History of Life (eds. D.M. Raup and D. Jablonski), pp. 167-182. Springer-Verlage, Berlin.
Lieberman, B.S., W.D. Allmon, and N. Eldredge. 1993. Levels of selection and macroevolutionary patterns in the turritellid gastropods. Paleobiology 19: 205-215.
Løvtrop, S. 1981. Macroevolution and punctuated equilibria. Systematic Zoology 30: 498-500.
Maurer, B.A., J.H. Brown, and R.D. Rusler. 1992. The micro and macro in body size evolution. Evolution 46: 939-953.
Mayr, E. 1982. Speciation and macroevolution. Evolution 36: 1119-1132.
McDonald, J.F. 1990. Macroevolution and retroviral elements. BioScience 40: 183-191.
McDonald, J.F. 1998. Transposable elements, gene silencing and macroevolution. Trends in Ecology and Evolution 13: 94-95.
Salthe, S.N. 1975. Problems of macroevolution (molecular evolution, phenotype definition, and canalization) as seen from a hierarchical viewpoint. American Zoologist 15: 295-314.
Stanley, S. 1979. Macroevolution. Freeman, San Francisco.
Stanley, S.M. 1982. Macroevolution and the fossil record. Evolution 36: 460-473.
Stanley, S.M. 1998. Macroevolution. Johns Hopkins University Press, Baltimore, MD.
Vrba, E.S. 1983. Macroevolutionary trends: new perspectives on the roles of adaptation and incidental effect. Science 221: 387-389.
Wright, S. 1982. The shifting balance theory and macroevolution. Annual Review of Genetics 16: 1-19.
I made the same mistake pretty early on when I jumped into the anti-creo wars. I heeded the advise of those who knew better than I and amended my arguments thusly, I trust that Greta will do the same.
Larry, in molecular terms how would you describe a macroevolutionary event? In my mind its something that involves a genetic bottleneck - a mass extinction leading to only a small number of genetically homogeneous survivors or a chromosomal alteration (such as the chromosome 2 fusion in human ancestors) - both of which will lead to a rapid alteration in the frequency of alleles in the population compared to the previous generation. Is this an incorrect way to think of it?
By the way don't be too hard on that videomaker, he isn't aiming at the scientific community. He is trying to reach the type of creationist that I have been arguing with on another site (here are this creationists 'killer' questions that 'evolutionists havent been able to answer'
"1. If man evolved from the monkey like creature where did the monkey like creature come from?
2. Did a male and female monkey creature evolve simultaneously?
(a) If yes what is the point of sexual organs? Why not just carry on evolving?
(b) If no where did the female monkey creatures come from, or the women of today?
3. How long did these monkey like creatures live for?
4. If it took millions of years for us to evolve, to produce fully functional body systems. Then how on earth did the chain carry on, at what point did the monkey like creatures stop evolving and start re-producing?")
To add to the list of references above, I'll also add a paper whose title pretty much sums up Larry's post!
Grantham, T. (2007) Is macroevolution more than successive rounds of microevolution. Palaeontology, 50, 75-85.
http://www.blackwell-synergy.com/doi/full/10.1111/j.1475-4983.2006.00603.x?cookieSet=1
This is the kind of genuine scientific debate that more evolution supporters need to be aware of.
martinc asks,
Larry, in molecular terms how would you describe a macroevolutionary event?
I don't think it's appropriate to think of macroevolution in molecular terms. That's the essence of the argument that macroevolution is decoupled from microevolution.
In my mind its something that involves a genetic bottleneck - a mass extinction leading to only a small number of genetically homogeneous survivors or a chromosomal alteration (such as the chromosome 2 fusion in human ancestors) - both of which will lead to a rapid alteration in the frequency of alleles in the population compared to the previous generation. Is this an incorrect way to think of it?
No, I don't think so. Both of the examples you give fall within the domain of microevolution.
Speciation by cladogenesis (splitting) is the beginning of a separation between microevolution and macroevolution. It's difficult to account for cladogenesis using standard population genetics. You need to take into account events that are outside of the evolving populations such as geography and climate. In a sense, macroevolution is about the interaction of evolving species with the environment over periods of million of years.
Species sorting, where two different species compete with one another and only one survives, is another classic example of a macroevolutionary event that cannot be explained by microevoution alone. It involves treating the species as the unit of selection but microevolution is only concerned with evolution within the species.
(N.B. I'm greatly simplifying species selection here in order to make the point that it differs from individual selection. Also, I'm personally not sure that species selection actually exists—that's part of the debate.)
Very interesting and informative!
It's difficult to account for cladogenesis using standard population genetics. You need to take into account events that are outside of the evolving populations such as geography and climate.
This distinction between micro and macro doesn't make much sense and I've said so before. Here are three examples: how would we account for them without considering no external factors?
-antibiotic resistance
-industrial melanism
-the phylogeography of any European species
Evolution below the species level is NOT about looking at only the gene pool and ignoring external factors.
There is legitimate scientific debate about whether macroevolution is more than just lots of microevolution or whether macroevolution encompasses mechanisms not seen in microevolution.
Mechanisms other than drift and selection? Such as??
Speciation by cladogenesis (splitting) is the beginning of a separation between microevolution and macroevolution. It's difficult to account for cladogenesis using standard population genetics. You need to take into account events that are outside of the evolving populations such as geography and climate. In a sense, macroevolution is about the interaction of evolving species with the environment over periods of million of years.
Why is it difficult? Clearly we weren't there, and have difficulty reconstructing population genetics from that perspective. But how id the interaction of evolving species within the environment "over periods of millions of years" different from "over periods of tens or hundreds of years" except in the timescale?
It's all well and good to have separate terms to describe different timescales, but as a biologist myself, I've yet to hear of macroevolutionary mechanisms being discussed that are exclusive from microevolutionary.
As the YouTube video that you link to suggests, the mechanisms are the same (in that case, growth).
In the comments, cladogenesis is mentioned. Again, that's a large-scale description of a great many small-scale events. As you say, it is difficult to describe such an array of events, and so we create terms for large-scale events to simplify explanations of so-called macroevolution.
What am I missing here?
windy asks,
This distinction between micro and macro doesn't make much sense and I've said so before. Here are three examples: how would we account for them without considering no external factors?
-antibiotic resistance
-industrial melanism
-the phylogeography of any European species
Evolution below the species level is NOT about looking at only the gene pool and ignoring external factors.
Point taken. It's not the distinction between whether external factors are important that counts.
The problem with microevolution is that it's very good at explaining evolution within a population but it fails as an explanation of how populations form in the first place.
Let's say you want to explain why there are four species of zebra. Can you do this using only microevolutionary phenomena?
Or let's say you want to explain why there are more marsupials in Australia than in Asia. Is there a microevolutionary explanation? Can someone who deals only with microevolution explain why there was a huge increase in the number of mammals about 65 million years ago?
dan says,
It's all well and good to have separate terms to describe different timescales, but as a biologist myself, I've yet to hear of macroevolutionary mechanisms being discussed that are exclusive from microevolutionary.
Everyone (but you) seems to agree that species sorting is such a mechanism. Please tell me why you; (a) never heard of it, or (b) disagree that it's separate from microevolution.
In the comments, cladogenesis is mentioned. Again, that's a large-scale description of a great many small-scale events. As you say, it is difficult to describe such an array of events, and so we create terms for large-scale events to simplify explanations of so-called macroevolution.
What am I missing here?
You're missing the step where two distinct populations are created where there used to be only one. How do you explain bonobos and chimps using only population genetics?
The key to macroevolution is the mapping of standard evolutionary mechanisms to the real world over very long periods of time. Just knowing the standard microevolutionary mechanisms isn't sufficient to explain the large-scale changes.
Larry,
Eldredge (1995) defines "species sorting" (also called "species selection) as "differential speciation or extinction of species within a larger group"; he clarifies that "Some lineages speciate at a higher rate than others, and some species are more prone to extinction than others" (119). These varying rates of speciation and extinction, according to Eldredge, produce definite patterns in the fossil record.
Now, to use the analogy contained within the YouTube video, all this entains is differential growth of competing branches that stem from the same trunk. It's still growth, albeit at a different scale at which new properties emerge.
At its most fundamental scale, however, these emergent properties still require microgrowth or speciation to be occurring. And as such, microgrowth and macrogrowth are NOT exclusive.
Also, Larry, you make my point for me:
"The key to macroevolution is the mapping of standard evolutionary mechanisms to the real world over very long periods of time."
Then go on to contradict yourself in the very next sentence:
"Just knowing the standard microevolutionary mechanisms isn't sufficient to explain the large-scale changes."
Which is it?
The creationists that will grant you microevolution but draw the line at macroevolution are not talking about Gouldian thought-experiments like species sorting. Some of them will even grant you speciation as long as it remains within a "kind."
From a scientific perspective, there is no need to invent any fundamentally different mechanism or process for macroevolution at any level, unless you believe reproductive isolation of populations to be such a process. Microevolution in the real world is always either about the interaction of genetics and environment (selection) or about random changes at the genetic level (in the case of drift).
Populations that become reproductively isolated (by any means, though I don't doubt that geographic isolation is the usual mechanism) are new populations whose gene pools are changed by drift and selection. If species-sorting processes are important, they occur because some populations survive and others go extinct due to classical population-genetic processes in changing (or not) environments. In the case of direct competition between related species, each is simply a part of the other's biotic environment, and as such can either be adapted to, or not.
Macroevolution is just the processes of microevolution, plus population fission. IMO.
Point taken. It's not the distinction between whether external factors are important that counts.
Thanks, but I'd have been more reassured if you hadn't used the "only population genetics" argument again in the very next comment! :o
Let's say you want to explain why there are four species of zebra. Can you do this using only microevolutionary phenomena?
1) Do you need macroevolution to explain the six or so subspecies of plains zebra?
2) How does macroevolution explain why there are four species of zebra? :)
You're missing the step where two distinct populations are created where there used to be only one. How do you explain bonobos and chimps using only population genetics?
How do I explain different populations of common chimpanzees using only population genetics? New populations can originate without speciation, you know :) Isn't it stretching macroevolution too far to say that it deals with the origin of populations?
dan says,
At its most fundamental scale, however, these emergent properties still require microgrowth or speciation to be occurring. And as such, microgrowth and macrogrowth are NOT exclusive.
Everybody agrees that microevolutonary mechanism are important in macroevoluton. The question is whether they are sufficient.
dan asks,
Which is it?
Both.
sven dimilo says,
Macroevolution is just the processes of microevolution, plus population fission. IMO.
Yes, we know that's the opinion of some people (mostly adaptationists). Other evolutionary biologists disagree. That's why there's a controversy.
windy asks,
How do I explain different populations of common chimpanzees using only population genetics? New populations can originate without speciation, you know :) Isn't it stretching macroevolution too far to say that it deals with the origin of populations?
I think you're avoiding the question.
How do you explain the formation of distinct populations within a species using only population genetics? What microevolutionary processes give rise to distinct populations?
I think you're avoiding the question.
No, I am making a point. You can't explain _anything_ about natural populations using "only population genetics" in the sense you mean, so I can't figure out why you imply that microevolution researchers are restricted to it.
But in fact, population genetics itself does not need to explain things without taking into account geography, climate and other external factors! See my three examples above.
What microevolutionary processes give rise to distinct populations?
Dispersal and vicariance.
Speaking of avoiding the question, is it your contention that every time there is more than one population, we are dealing with macroevolution?
oh, and selection might also give rise to distinct populations, but at that point we might say we're dealing with speciation.
Larry,
Maybe I'm misunderstanding you on how you're defining microevolution, because you keep bringing up population genetics as a proxy. I'm referring to it as speciation, which, just as in your zebras and chimps analogies, regularly involves geographical and climatological factors that exceed the explanatory capacity of popgen. Or does it? - population genetics IS impacted by those and other environmental factors.
So I'm still struggling to understand how you see the species sorting of zebras, hominids, or other examples, outside of the microevolutionary modes of drift and selection. You mention species sorting - how is that different from a description of two popgen models where one population thrives and the other crashes (which could happen for various reasons compatible with microevolution)?
For instance, you ask:
"How do you explain the formation of distinct populations within a species using only population genetics? What microevolutionary processes give rise to distinct populations?"
I'll give you two: (1) geographical isolation; and (2) diversifying selection.
Thus, I have to conclude that the makers of the video are as ignorant of evolution as the creationists they mock.
That seems hardly fair. The video in question isn't really discussing the possible distinction between micro- and macroevolution. (Call it framing if you must.)
cdk007 is the prolific author of such movies like The Evolution of the Flagellum (which IIRC is consistent with Nick Matzke's old Talk Origins flagellum essay with one or two errors), and the recently popular Evolution IS a blind watchmaker which ingeniously shows how to build a 24 hour:minute:second time piece with a genetic algorithm.
In cdk007's consistent ending catch phrase: "Think about it."
What I can say is that this thing of competing species is not good when it comes to model biogeographic colonization and other ecological changes, where models of drift prove to be much more predictive than models of species competition.
Describing differential survival at any level as if a "selection" has happened is of very little help as far as science goes. Remember, selection is just slection. The mechanisms that generate variation will still require other forms of explanation.
How can species competition produce any evolution? If one species wipes out another, that is a consequence, not a cause, of any "advantage" it may have had under a given circumstance. Selectionism at all levels frequently misleads into this teleological-like thinking.
Evolovability, for sintance. I doubt very much than anyone can present any evidence that the average "evolvability" of species has increased along the biological history of earth. MY feeling is that evolovabilty can increase or decrease anytime. pecilaization and generalization, they both continue to occur, no matter how much "selection".
Sources like those listed by tr gregory give a clue that micro/macroevolution are not terms invented by Creationists. To those, I'd add "Evolution above the Species Level" by Bernhard Rensch (English translation published 1959) and Eldredge's "Macroevolutionary Dynamics" (1989).
I'd say it's but another case of Creationists using sciencey-sounding words to pretend that they're smart; they really don't understand what microevolution and macroevolution are.
Correction noted in the blog. Thanks for calling my attention to it.
-Greta Christina
Greta Christina's Blog
I read Dr. Moran's linked essay/book chapter on Macroevolution, and I still don't get it.
What, exactly, are these processes and patterns that can't be explained by selection and drift within populations, together with the fission of populations due to (thanks windy) dispersal and vicariance?
Species sorting? In hindsight we look back and see that some species/genera/families/orders etc. have flourished and radiated, others have not, and most have done OK for a while then disappeared. But if we had a time machine, we could go back and verify that all of these species, whether destined in the future to radiate or to go extinct, all consisted of populations, (metaphorically) dealing with the contingencies and vicissitudes of their biotic and abiotic environments with the genetic variance available to them; and that all those populations consisted of individuals that ended up having some finite number of surviving descendants.
What's so different? Isn't microevolution the mechanism of macroevolutionary pattern? And if not, why not?
Sven DiMilo asks,
What, exactly, are these processes and patterns that can't be explained by selection and drift within populations, together with the fission of populations due to (thanks windy) dispersal and vicariance?
Species sorting?
Yes. I think it's far to say that all knowledgeable evolutionary biologists admit that species sorting is a higher level process that can't be explained by evolution at the level of individuals within a population.
Group selection falls into the same category but it's not the same as species sorting.
I'd don't have the time, or desire, to explain species sorting. Read The Structure of Evolutionary Theory by Stephen Jay Gould.
"Read The Structure of Evolutionary Theory by Stephen Jay Gould."
Ah, the appeal to the Master. Right, I'll read that tonight and get back to you tomorrow.
But in the meantime, since you are disinclined to explain any of your knowledgable pronouncements from on high, let me give it a shot, and you can criticize, OK? That's how you like the dialogue to work here at the Sandwalk, it seems.
So. Species or clade sorting results from differential extinction and speciation among species considered as the unit of selection. Now, any post-hoc hindsight view of evolutionary history will certainly observe such differential extinction and speciation; some clades are still around, and quite diverse, others are barely hanging on, and many others are no more.
But this special Gouldian species-sorting thing requires more than a post-hoc accounting of evolutionary successes and failures, it postulates that the pattern is due to something about the species involved--some intrinsic emergent property of the species level that operates above and apart from those boring ol' microevolutionary mechanisms.
Right? So my question is, like what? Species-intrinsic properties that I have seen referenced are things like "extinction propensity" and "speciation rate."
Am I being stupid? I just don't see how the likelihood of a species going extinct is anything but the likelihood of its component populations going extinct, and I know that populations go extinct when recruitment rates are lower than death rates--and it's individuals being born and dying.
You don't have to deign to explain it to me, but please just give me a hint so that if I do tackle the profuse verbiage of Gould's Brick, I'll have a search image in the jungle.
Sven DiMilo says,
You don't have to deign to explain it to me, but please just give me a hint so that if I do tackle the profuse verbiage of Gould's Brick, I'll have a search image in the jungle.
You're not going to read up on species sorting, are you? You've already made up your mind.
I think it is fair to say that many, probably most, evolutionary biologists do not think there is any consitutively different mechanism for macroevolution than for microevolution, the one reflecting the accumulation of the other: macroevolutionary questions are made for comparisons across greater phylogenetic distances (and more remote common ancestors).
As far as the debate over the units of selection, genes, organisms, and some hihger level social organization units (for instance, termite clone-nest) are acknowledged units of selection but not so species or clades. I guess what I want to clarify is that the actual importance of species selection is a controversial topic, up for discussion.
The argument in Gould's book actually unfolds across several chapters, so it is not very useful to tell someone to "read gould". I myself will concede that gould is right in pointing out to supra-individual units that have a clear biological reality: for instance, in eusocial insects. I freely agree that a greater, higher level unit has emerged that has allowed the evolution, for instance, of sterile workers. Gould however takes this as evidence of group selection. I don't. Systems theory is much more enlightening as to how these higher level units develop and evolve.
Gould himself recognized that the debates over levels of selection would probably never go away and even suggested that the controversies could be beyond the ability of the human brain to resolve. If that is not a warning, I dont know what is.
Larry,
You're not going to read up on species sorting, are you? You've already made up your mind.
What is there for him to make his mind up about here? You're not even trying to explain anything.
For myself, I don't have the book by Gould handy to read up on, so I read the material that I could find from Eldredge on it, and quoted it here. Same response from you: nada.
Dan says,
What is there for him to make his mind up about here? You're not even trying to explain anything.
I'm not under any obligation to explain the concept of species sorting. What I object to is when people dismiss it without understanding it. That doesn't seem like a good way for scientists to behave.
The point about species sorting is that, properly understood, it is a higher level process where the survival of related species in a clade is dependent on emergent properties that belong to the species but not to any individual within the species.
It is generally understood that this would be a clear example of a macroevolutionary process that cannot be sufficiently explained by microevolution. The debate concerns whether there are any real-life examples of species sorting.
There are two reasons why I'm not trying.
(1) I'm not convinced that it exists and I don't want to be put in the position of having to defend something that I don't support.
(2) It's very complicated.
For myself, I don't have the book by Gould handy to read up on, so I read the material that I could find from Eldredge on it, and quoted it here. Same response from you: nada.
In the posting that I saw above you included speciation in our definition of microevolution. That's such an unusual definition of microevolution that I'm not sure we can have a meaningful discussion.
Sanders says,
Gould himself recognized that the debates over levels of selection would probably never go away and even suggested that the controversies could be beyond the ability of the human brain to resolve. If that is not a warning, I dont know what is.
It's a warning not to make dogmatic statements like "macroevolution is nothing more than lots of microevolution."
The best you can say, if you're inclined to believe that, is, "there is considerable debate about the sufficiency of microevolution to explain macroevolution, I favor the side that says there are no higher level processes that distinguish macroevolution from microevolution and, furthermore, I favor a definition of macroevolution that is compatible with the idea that macroevoluton is no more than cumulative microevolution."
In his most recent book (The Ancestor's Tale) Richard Dawkins has adopted this position and I think it's quite admirable even though he uses self-serving definitions (p. 498).
I must mention the alleged distinction between macroevolution and microevolution. I say "alleged" because my own view is that macroevolution (evolution on the grand scale of millions of years) is simply what you get when microevolution (evolution of the scale of individual lifetimes) is allowed to go on for millions of years. The contrary view is that macroevolution is something qualitatively different from microevolution. Neither view is self-evidently silly.
You're right--I'm not going to go read Gould on species sorting very soon, but it's not because I've already made up my mind (it's because I have piles of exams and lab reports to grade--I am procrastinating on this as I type--and higher spare-time-reading priorities).
I agree with Dawkins on this point, at the moment, by virtue of Occam's Razor: I know microevolution happens and I see no reason to postulate additional mechanisms (other than population fission plus lots of time) to account plausibly for macroevolutionary patterns. The sticking point for me is that I have yet to hear a good example of an "emergent property that belongs to the species and not to the populations that make up that species." Microevolution itself is an emergent property at the population level, and I see nothing sepcial about a "species" that warrants granting it additional properties. I was fishing here for such an example, but nothing doing--it's a wade into the Gouldian swamp of over-writing or nothing. *shrug*
I'm not under any obligation to explain the concept of species sorting. What I object to is when people dismiss it without understanding it.
Which is why I am asking that you help me explain it. I won't speak for others here, but for myself I'm trying to understand it, and you're not helping. This is your blog - if you're not interested in discussing/explaining your viewpoints, why do you blog on them in the first place? You know full well that there is legitimate room for even knowledgeable biologists to question your claim that macroevolution includes mechanisms that are not merely emergent from microevolution, yet you began with an off-handed dismissal of those experts that disagree with you.
So don't give us bullshit that we're the ones who have not been behaving well for scientists.
You also say:
In the posting that I saw above you included speciation in our definition of microevolution. That's such an unusual definition of microevolution that I'm not sure we can have a meaningful discussion.
Then correct me. Don't be an ass. If you would re-read my initial comment here, you would see me asking "What am I missing here?" You said 'species sorting' in a manner that didn't illuminate much. And now you mention that you're not even sure that your justification for being an ass is correct?!
That said, the clarification that you offer Sanders makes a bit more sense. It had seemed to me that you were dismissing Greta's point just as dogmatically as that which you decry - I see that I stand corrected. Thank you for correcting me instead of being dismissive. For my part, I'm sorry if I appeared hypercritical - but it really does seem to me that it is as simple as micro + time = macro. That's skepticism for you.
I have nothing against species selection in principle. But that doesn't help clarify your "more than population genetics" definition. I'd like to know what the least common denominator of macroevolution is. Is everything involving more than one population macroevolution? Above, you even hint that group selection might be macroevolution? What the heck isn't macroevolution, then?
Should we conclude that since the Wahlund effect results by definition from the presence of more than one (sub)population, it's therefore macroevolution and unexplainable using population genetics?
I wrote a long essay about Macroevoluton. It's clear to me that some of the critics on this blog haven't even bothered to read my essay.
That's very sad because it took a lot of effort and almost a decade of thinking about the subject.
"...results by definition...": sorry for the sloppy writing above, I meant of course that the definition requires it, not that substructuring will always lead to the W.E.
I don't agree that population genetics = microevolution. Microevoluton is more than that level of description. A clear connection to discussion of phenotypic changes must be made and contrasted with the actual biological and ecological facts. This includes an explicit history of environmental effects on the phenotype (which can do such interesting things like hiding genetic differences)
I consider microevolution to include evolutionary transitions that are well documented. I would include speciation; it is also within the domain of the study of microevolution; mechanisms like pre and postzygotic isolation, lesser and greater degrees of speciation can be observed in the field; many times it is a fairly recet event and therefore can be well-documented; For instance, the origin of new species of plants by alopoliploidy, or hybrid specis of insects. These mechanism os speciation can hardly be called "darwinian" and population is of little insight compared on what we can gain by simply studying the karyotipes.
.
So, microevolutionary studies of speciation are possible. And, microevolution is NOT equal to "population genetics" or " darwinian selection". Other evolutionary mechanisms are also going to be part of microevolution.
I read the essay. In fact, I just clicked on your link and read it again. I'm sorry to report that it didn't help to clarify my understanding of why the "sufficiency of microevolution hypothesis" ought to be discarded. After a fine treatment of the history of this controversy, there are simply assertions, by you and quoted from Gould and Eldredge, that microevolution is insufficient. But see, that's what I'm not getting--why is it insufficient?
That higher-level patterns are identifiable in hindsight does not require that new mechanisms are necessary. And statements like "Since speciation is not a direct consequence of changes in the frequencies of alleles in a population, it follows that microevolution is not sufficient to explain all of evolution." don't help--it's the premise I don't get. Why is speciation more than the simultaneous changes in allele frequencies in two populaitons that lead to reproductive isolation?
But you're right--you're under no obligation to explain or try to convince me. And likewise, I'm under no obligation to buy into your unexplained conclusions just because you've been thinking about it for 10 years.
I consider that microevolution usually refers to the differences that may evolve between closely related populations (or species; or within a population, such as sexual dimorphism) whereas macroevolution refers to the greater differences that we find as we compare sucessively more distant taxa ("body plans", for instance)
Ditto on what Sven said.
I wrote a long essay about Macroevoluton. It's clear to me that some of the critics on this blog haven't even bothered to read my essay.
Do you count me as one of these critics? I didn't find an answer to my population question there. You quote Ridley saying
Microevolution therefore refers to changes in gene frequency within a population .... Macroevolutionary events are more likely to take millions, probably tens of millions of years. Macroevolution refers to things like the trends in horse evolution described by Simpson, and occurring over tens of millions of years, or the origin of major groups, or mass extinctions, or the Cambrian explosion described by Conway Morris. Speciation is the traditional dividing line between micro- and macroevolution.
There is a world of evolution happening between one single population and macroevolutionary changes taking millions of years. Is the dividing line perhaps hidden behind those four dots?
I'm not trying to nit-pick, but I think the definitions offered in this thread are contradictory. Imagine a simple population which is divided in two by a geographic barrier. Is that macroevolution?
I like Larry's essay. There is indeed a historical context in which the neodarwinian dogmatism of population genetics would hinder any serious consideration of macroevolutionary patterns.
Macroevolutionary patterns are fascinating, for instance, punctuated equibilibrium. But I specially like the correspondence betwen geological change and speciation, For instance, the number of species of molluscs has raised cintinuously since the atlantic coasts of south america and africa have become available... and then we have the asteroids, and fluctuations in the composition of the atmosphere...
Whta I am trying to say ifs that this pattern is more accidental, drift like: THIS is what becomes apparent to me from macroevultionary analysis. It is NOT guided by some higher level (specis level) process of selection; but a process of DRIFT. Of available resourcs and accidents of colonization. As I already mentioned above, models of drift rather than competition among species are better predictors of the ecology that will develop in a colonization process.
There is no such thing as "survival of the fittest" perfecting any new organic changes at the level of species selection.
I do not believe in species selection. Further, while study and description of microevolution and macroevolution can be very different, there is indeed a link: microevolutionary changes are conserved in a lineage, and are in efect the "steps" of the more long term, macroevolutionary pattern.
macroevolutionary patterns have all to do with geology and biogeography: NOT species selection
"Since speciation is not a direct consequence of changes in the frequencies of alleles in a population"
True
"it follows that microevolution is not sufficient to explain all of evolution"
No, speciation can be observed in our small, neontological scale. I consider it part of microevolution.
macroevolution is obviously a domain in itsefl at another scale that needs to follow up on ong-term geographicgeological changes too. It is not reducible to microevolution. Nevertheless, there has been much talk about macroevolution in terms of differente evolutionary mechanism, rater tahn a different level of bservation. Specially, some evo-devo people argue that microevolution is true for speciation an adaptation, but not a good explanation for the apparently non-adaptive difference in phyla body plans. The cambrian "explosion"would be the result of some kind evolutionary happenstance that somehow changed is argued to be outside the the kind of things that we can observe in microevolution. Thye argue, for instance, that this coud relate to the evolution of a very unique, archetypical gene regulation network (I don't buy it).
How can a mechanism produce body plan differences without ot involving microevolution? What ARE these non-microevolutionary mechanisms that they may produce organic evolution? How?
I think the cambrian explosion, is much like a new shoreline for molluscs, or when vertebrates moved to dry land, or to flying. You will see an increase in the number of species, which has more to do with occupation of a previously unexplored lifestyle or resource, than with the violation of regular microevolutionary mechanisms.
Sanders and Sven,
If it helps, I noticed (a bit belatedly, but still) that John Wilkins has an entry up on the TalkOrigins site on Macroevolution: It's definition, philosophy and history. It's a much better explanation of the controversies (surrounding disagreements over definitions) and reductionist arguments than Larry's, IMHO, which doesn't clarify definitions very well.
And FYI, since a pingback did not appear... I continued this thread seeking better explanations over at my blog, Migrations.
Daniel said,
If it helps, I noticed (a bit belatedly, but still) that John Wilkins has an entry up on the TalkOrigins site on Macroevolution: It's definition, philosophy and history. It's a much better explanation of the controversies (surrounding disagreements over definitions) and reductionist arguments than Larry's, IMHO, which doesn't clarify definitions very well.
My essay was written as a rebuttal to John's. That's why I quote him at the start of my essay.
I'm sorry if you find my definitions of macroevolution difficult to understand. I tried to support them wherever possible with quotations from evolutionary biologists who actually study macroevolution. John gives you his version of macroevolution.
I think you still don't get one of the main problems. Those who study macroevolution think of it as a discipline that attempts to decipher the real history of life on Earth. This history includes things like ice ages and mass extinctions and how they affected life.
Saying that microevolution is all that's needed to understand macroevolution is like saying that relativity and quantum mechanics are sufficient to explain the formation of our particular solar system.
Larry,
Yes, I'm aware that I'm not understanding everything you're saying - some of it comes off as counter-intuitive to me, and therefore difficult to grasp. That's why I started off asking for better explanations, to help understand your point of view (and I assumed that you had a valid point from the beginning, that I wasn't fully grasping). Instead I got off-handed dismissals and insults of being "sad" and "dogmatic." It made you sound arrogant and motivated only to shove your dogma to me from up on high.
That said, I'm sorry, I did skim over the intro to your essay and mention of Wilkins. As such I only stumbled on it later.
And I've been giving it some more thought in the past day, trying to understand both your and Allen's comments better (Allen I think agrees with you, and he has my utmost respect for his patience at explaining such things). Reference to the concept of cladogenesis alone didn't seem to me to be more than microevolution of divided populations, hence my skepticism. But Allen put it in contrast to anagenesis, reinforcing the line between micro and macro at speciation, and in the context of punctuated equilibrium. In other words - microevolution can be viewed as the change over time of one species, while macroevolution is change over time of more than one species. I imagine that's what you were getting at earlier. And that's a completely valid way of looking at it, I think, which completely supports your argument.
But placing emphasis on the term speciation (or at any other level of hierarchy) is just one perspective. As it's been noted, definitions of macroevo and microevo vary depending upon whether it's a geneticist or an ecologist doing the talking. Does that mean that one's right and the other is wrong? I seriously doubt that. But speciation IS an arbitrary term, because species are not fixed entities, and there is no mechanism of speciation outside of adaptive and non-adaptive modes of change, right? All of common descent follows from that.
So, from the perspective of mechanisms at the genetic level (viewing genes as evidence of common descent), then Wilkins position is completely valid in its own right. I just happen to share that viewpoint.
So when you say:
"Saying that microevolution is all that's needed to understand macroevolution is like saying that relativity and quantum mechanics are sufficient to explain the formation of our particular solar system."
... I say that I agree completely, in terms of practical understanding. That's simply too much material for us to grasp without higher-order explanations. In theory, however, the formation of the Universe was propogated from such reductionist natural laws however, right?
It's all too much information for anyone to understand at all levels though, which is why we have different explanatory models for different hierarchical levels. I think.
Does that sound about right? (Either way, I really do appreciate the explanation, finally - as you said, these are NOT simple concepts)
Dan,
I'm glad you are beginning to see the point.
Let me restate it in order to make it more clear.
When someone says that macroevolution is simply lots and lots of microevolution they are making a dogmatic statement that doesn't reflect the true science.
What they should be saying is ...
There is considerable controversy in the scientific community over the sufficiency of microevolution to explain macroevolution. By some definitions of macroevolution—those not used by most people who study macroevolution—it is possible to take the position that microevolution is sufficient to explain macrevolution provided that one rejects hierarchical theory. That's the position I take after having studied the controversy.
That's just a wee a bit of an overstatement though, don't you think? Now it sounds as though you're trying to marginalize the gene-centric viewpoint.
Not to mention, the last sentence, "That's the position I take after having studied the controversy." Sounds kinda egotistical to me, but again, I shouldn't be surprised at that given how this conversation has gone - how about just "That's the species-centric position"?
The analogy is fit. The solar system could have been different. But we would still understand it through the laws of physics. Without them, all we have is a description. We don't have a different physics for each solar system. macroevolution does ot violate microevolution; rather, without microevolutionary mechanisms, macroevolutionary patterns would not be possible: not the other way round.
I think the "macro" in macroevolution should refer to deep time and long phylogenetic distances. I think it is misleading to think of macroevolution as speciation or biogeoegraphic environmental changes, that can occur in quite small time scales and with great phylogenetic proximity. Cleary the notion of macroevolution is intended to describe long processes such as the origin of mammals, for instace. It's all bout scale, and not so much about specific hypotheses (particlarly so, species selection)
Larry,
Also, you said:
"When someone says that macroevolution is simply lots and lots of microevolution they are making a dogmatic statement that doesn't reflect the true science."
Since when is the genetic record, or phylogenetics, not true science? The genetic record is one of the most convincing evidences of macroevolution, and that there is no distinction between macroevolution and microevolution at the gene level. Genes don't know the difference between cladogenesis and anagenesis.
Dan says,
Since when is the genetic record, or phylogenetics, not true science? The genetic record is one of the most convincing evidences of macroevolution, and that there is no distinction between macroevolution and microevolution at the gene level. Genes don't know the difference between cladogenesis and anagenesis.
This is one of the ways in which it's so easy to go wrong.
The comparison of sequences is, indeed, one of the most powerful bits of evidence for evolution. It reveals that we all share a common ancestor and it provides enormously powerful support for the concept that evolution requires change in the frequencies of alleles in a population over time.
However, a comparison of the horse genome and the elephant genome tells us absolutely nothing about the actual history of the evolution of horses. You can't make those famous horse trees from the sequences of the survivors.
Furthermore, if you're interested in whether morphological change is associated with cladogensis or anagensis then staring at sequences isn't going to help. The patterns of macroevolutionary change, which form the basis of marcoevolutionary theory, just aren't accessible via sequences (with a few exceptions).
One of the most interesting problems in macroevolution is the Cambrian explosion. The sequences, for the most part, tell us that it never happened but the fossil record suggests otherwise.
As I say in my essay ...
If we could track a single lineage through time, say from a single-cell protist to Homo sapiens, then we would see a long series of mutations and fixations as each ancestral population evolved. It might look as though the entire history could be accounted for by microevolutionary processes. This is an illusion because the track of the single lineage ignores all of the branching and all of the other species that lived and died along the way. That track would not explain why Neanderthals became extinct and Cro-Magnon survived. It would not explain why modern humans arose in Africa. It would not tell us why placental mammals became more successful than the dinosaurs. It would not explain why humans don't have wings and can't breathe underwater. It doesn't tell us whether replaying the tape of life will automatically lead to humans. All of those things are part of the domain of macroevolution and microevolution isn't sufficient to help us understand them.
"but the fossil record suggests otherwise"
We have traces of burrows and Kimberella ( a mollusc, a derived protostome) from the precambrian. Plus molluscan spiral-cleaving patterns in fossil embryos.
Hard parts also fossilize more easily than soft and small invertebrates, which helps explain the much greater record in the cambrian, when hard body parts and increased body sizes evolve.
I think there is no evident inconsistency between the molecular and fossil data. The main lineages of metazoans had already diverged before the cambrian "explosion".
Saying that microevolution is all that's needed to understand macroevolution is like saying that relativity and quantum mechanics are sufficient to explain the formation of our particular solar system.
Ah, but saying that we can't in practice reduce macroscale events is subtly different from the claim that "macroevolution is more than repeated rounds of microevolution". Would you say that solar system formation is something more than repeated rounds of quantum mechanics? Or relativity?
Sanders says,
I think there is no evident inconsistency between the molecular and fossil data. The main lineages of metazoans had already diverged before the cambrian "explosion".
I don't disagree. Nevertheless, there seems to have been a remarkable change in morphology of a number of lineages in a short period of time. That's not something that's predictable from simply examining the sequences of present day species.
Furthermore, there were a number of lineages that went extinct by 500 million years ago. Those extinctions help inform us about evolution. For example, they give rise to Gould's hypothesis that diversity was greater in the past than today. You can't get that sort of data from sequences.
Windy says,
Ah, but saying that we can't in practice reduce macroscale events is subtly different from the claim that "macroevolution is more than repeated rounds of microevolution".
It's more complicated than that. What paleontologists are saying is that deciphering the history of life requires a lot more than just microevolution. What you're missing is the fact that macroevolution isn't defined the way you think it is.
In addition, there's the possibility of things like species sorting which really are uncoupled from microevolution.
If Eldredge & Gould are correct and punctuated equilibria are common patterns in evolution then even that is something that cannot be fully explained by microevolution. There's nothing in microevolution that predicts an association between visible evolution and cladogenesis.
Larry,
I wasn't using genetics in terms of "comparative genetics" - I was referencing genetics as the fundamental unit of heredity. Whereas looking at evolution from the perspective of species and populations yields a discontinuous landscape, looking at evolution from the perspective of the heredity (and the units of it) yields a continuous landscape.
Perhaps I shouldn't use the word macroevolution to describe what I'm talking about though. I'm talking about descent and ancestry, more specifically. Literally speaking, we can theoretically trace our ancestry back to the common ancestors that reunite us with other species, phyla, even domains of life. That's not the way we process the data (how could we), but it's the theoretical conclusion. This interpretations seems to jibe with what you're saying - or at least the excerpt that you just quoted from your essay.
As you and Allen have been pointing out, my definitions of macroevolution and microevolution appear to be quite off the mark however. There is a history stemming from the modern synthesis that I'm not fully versed in, being a much younger student of science. And I'm not formally educated as an evolutionary biologist.
But given these definitions of macroevolution and microevolution, I think that the founders of the modern synthesis may have chosen their labels poorly. Intuitively, they conjure notions of continuity between "lots" and "little" change.
It's more complicated than that. What paleontologists are saying is that deciphering the history of life requires a lot more than just microevolution. What you're missing is the fact that macroevolution isn't defined the way you think it is.
How do you know? I haven't offered a definition, I have asked you to clarify your definition.
There's nothing in microevolution that predicts an association between visible evolution and cladogenesis.
Assortative mating? Niche separation?
The cambrian looks to me like the "typical" extinction-and-replacement pattern, stepping in after the ediacaran fauna, though I will grant that a different ecology originated (large predators).
I don't think the cambrian has specially high taxonomic diversity; in fact, the earth in general has less species diversity since dry land had not yet been invaded by groups such as the vertebrates, for instance. Remember, also, that species diversity is much greater on land than on sea. It is a fact that species diversity on aerth has increased since the cambrian
The only thing that we can argue si that more "phyla" were present in the cambrian. I would expect some cambrian lineages to go extinct, but I also believe we have a fair surviving sample of the main groups originated in that time.
Many of the "bizarre" phyla argued by gould have been demonstrated to belong to known phyla; odontogriphus was a mollusc; amiskwia, a chaetognath; Hallucigenia, an onychophrona; the list continues. Further, many are not so bizarre that we may not recognize some affnity, such such as ecdysozoa, for instance. In summary: cambrian is not SOOO weird.
I think it is important to understand that the fact that we can account for a greter number of "phyla" than what survives nowadays does not mean that something particularly exceptionla was going on. YOu must corrct your phylogenetic scale. These are speciaition events like any other but becuase they happened very long ago, these twigs have become the basalmost branches when the later forms are included. For instcne, if you were to look in the triassic, you could surely say there were many ore "classes" of tetrapods then than now. THis is why it is important to correct the common misconception of invoking some "special mechanism" without considering this simple "phylogenetic scaling". This looks more to me like an ecological radiation of the bilateria, like that of many other groups that we may choose to observe in the fossil record.
Sanders, I wasn't invoking any special mechanism for the Cambrian explosion. I'm well aware of the distinction between phyla and their origins as speciation events. (So is Gould, BTW, in spite of the fact that some people think he's stupid.)
All I'm saying is that we wouldn't even be discussing these problems if all we had to look at were sequences. They are clearly macroevolutionary problems that have very little to do with microevolution.
I mereley wish to increase your awareness that some BS is being pushed under the banner of macroevolution. Many "grand men" of evo-devo believe that some unique mechanism happened in the cambrian allowing for "phylum-grade" differences (rather than mere "species-grade" differences, where "regular" micorevolutionary mechanisms would be at work).
I also happen to think that species selection is not very enlightning to understanding macroevolutionary patterns.
Post a Comment