The poles are closed and the results are in. Richard Dawkins is the clear winner (boo!).The good news is that 87% (499/573) Sandwalk readers have legitimate scientific views of evolution (Dawkins + Gould + Futuyma). Only a small number of readers are creationists or proponents of theistic evolution.
The bad news is that most readers are split between three different views of evolution. Some people have asked me to explain these three views so here's a brief summary of how I distinguish between Dawkins, Gould, and Futuyma.
Richard Dawkins holds the Charles Simonyi Chair for the Public Understanding of Science at Oxford University (UK). In his first book, The Selfish Gene (1976), he promoted the idea that evolution can be viewed as a competition between genes. This concept was amplified in The Extended Phenotype (1982) where he also answered the main criticism of the selfish gene concept. Dawkins' most popular book was The Blind Watchmaker, first published in 1986. In that book he made the case for design by natural selection and attempted to dismiss, or minimize, all other mechanisms of evolution. The emphasis on the power of natural selection was expanded in Climbing Mt. Improbable (1996). Dawkins is the leading exponent of adaptationism—or Ultra-Darwinism—the idea that everything interesting in evolution can be explained by adaptation. This is especially true of traits that give rise to visible phenotypes. Dawkins is not very interested in macroevolution and he dismisses punctuated equilibria and species sorting. He believes, along with most adaptationists, that macroevolution is just an extension of natural selection acting on populations. (See RichardDawkins,net for a complete list of books and articles.)
Stephen Jay Gould was Alexander Agassiz Professor of Zoology at Harvard University from 1967 until his death in 2002.He published Ontogeny and Phylogeny in 1977 where he made the case for a relationship between development and evolution. In The Mismeasure of Man (1981) he criticized biological determinism. Wonderful Life (1989) described the Burgess Shale fossils and explained Gould's ideas about the role of chance and contingency in evolution. In 2002, Gould published The Structure of Evolutionary Theory where he attempts to explain macroevolution, punctuated equilibria, and species sorting. These are part of Gould's hierarchical approach to evolutionary theory. Gould identifies himself as a pluralist—one who recognizes many different mechanisms of evolution that can give rise to important and interesting features. He tends to place much more emphasis on chance and accident in evolution than Dawkins.
Gould, along with Niles Eldredge, is famous for the concept of punctuated equilibrium. This is the idea that much of the change in the characteristics of species is concentrated in brief speciation (by cladogenesis) events.
Gould wrote a regular column for Natural History magazine and many of his articles have been collected in a series of anthologies: Ever Since Darwin, The Panda's Thumb, Hen's Teeth and Horse's Toes, The Flamingo's Smile, Bully for Brontosaurus, Eight Little Piggies, Dinosaur in a Haystack, Leonardo's Mountain of Clams and the Diet of Worms, The Lying Stones of Marrakech, and I Have Landed. Some of his essays and some of his scientific articles are widely cited. (For a complete list see SJG Archive.)
Douglas J. Futuyma is a Professor of Ecology & Evolution at the State University of New York at Stoney Brook. He is best known for his textbooks on evolution; Evolutionary Biology (1998) and Evolution (2005). His major research interests are evolutionary theory [see Hypotheses, Facts, and the Nature of Science] and the interactions of plants and insects [see Insect Pests: Resistance and Management].Futuyma's view of evolution is different from that of Richard Dawkins because Futuyma is interested in random genetic drift and speciation. Futyuma is much more aware of population genetics than Dawkins or Gould and he (Futuyma) frequently refers to it in his books and papers. Unlike Gould, Futuyma is skeptical of punctuated equilibria and particularly species selection/sorting, although, ironically, he is credited with proposing the best explanation of the connection between cladogenesis and evolution.
You can check out some of Futuyma's ideas in this interview. In response to the question, "Is natural selection the only mechanism of evolution?", Futuyma replies,
No, certainly not. There cannot be evolution without genetic variation in the first place. So there must be mutation and often recombination to generate the different genotypes or the different versions of the genes, known as alleles, which then may or may not make a difference in the ability of an organism to survive and reproduce. You can’t have any evolutionary change whatever without mutation, and perhaps recombination, giving rise to genetic variation. But once you have genetic variation, there are basically two major possibilities:Neither Gould or Dawkins would respond in this way. Dawkins would admit to random genetic drift but downplay its importance. Gould would focus on higher mechanisms of evolution like species sorting.First, there is simply no difference between the different genotypes or different genes in their impact on survival or reproduction, and in that case, you can have random changes of one versus the other type in a population or a species until eventually one replaces the other. That is an evolutionary change. It happens entirely by chance, by random fluctuations. That is what we call the process of genetic drift.
Genetic drift is very different from possibility number two, natural selection, which is a much more consistent, predictable, dependable change in the proportion of one gene vs. another, one genotype vs. another. Why? Simply because there is some consistent superiority, shall we way, of one genotype vs. another in some feature that affects its survival or some feature affecting its reproductive capabilities.
Futuyma also thinks about the role of mutation in a different way than either Dawkins or Gould, especially Dawkins. While Dawkins is very much opposed to crediting mutations per se with any substantial influence on evolution, Futuyma is more sympathetic to a limited mutationism point of view. For example, when asked what would happen if the tape of life were re-played he says.
Of course, it wouldn’t be the same, because first of all, random processes are involved in the evolutionary process. For example, the origin of new mutations: a lot of evolution is dependent on particular mutational changes in genes that were very, very rare or unlikely, but that just happened at the right time, in the right species, in the right environment, but it need not happen that way. So, there’s this unpredictability.This is very unlike Dawkins who is more inclined to think of evolution as design and strongly resists any attempt to sneak randomness into the equation. For the most part, Dawkins believes that all possible mutations will be available for selection so mutations can never determine the direction of evolution. Gould prefers to focus on developmental constraints as possible limits to the effectiveness of natural selection.
As an interested non-biologist who voted for Dawkins, at least partially because Gould's prose style tends to annoy me, I've been reading these posts with interest.
ReplyDeleteI guess my question is this:
Would you say there were any irreconcilable differences in opinion between the three views you lay out? Or is it principally a question of emphasis?
Harry
The good news is that 87% (499/573) Sandwalk readers have legitimate scientific views of evolution (Dawkins + Gould + Futuyma). Only a small number of readers are creationists or proponents of theistic evolution.
ReplyDeleteThe ratio is probably even higher than that. I abstained from voting on grounds that I am not familiar enough with the distinctions between Dawkins, Gould and Futuyma, and I suppose others might have as well.
I prefer Dawkins' writing to that of Gould, but that doesn't have a whole lot to do with their views on evolution, and I haven't read anything by Futuyma. I also prefer Dawkins' view on religion to that of Gould, although again this is irrelevant to the poll question.
I'm really surprised Futuyma didn't receive more votes. I even sent a couple ignorant friends over here to vote for Douglas! This was on day one though, so the running was much more close at the time.
ReplyDeleteDamn. I guess this poll just goes to show that sheer publicity affects the public's scientific understanding more than the science itself.
I can't remember if I voted for Futuyma (the only genuine professional evolutionary biologist of the 3) or abstained because it was a silly question.
ReplyDelete"I guess this poll just goes to show that sheer publicity affects the public's scientific understanding more than the science itself."
ReplyDeleteWell, nobody's going to vote for someone they've never heard of, and unless one has used Futuyma's textbook in a course on evolutionary biology (I'll date myself here by admitting I still have my copy of the first edition!), there is no reason for "the public" to have heard of him. I didn't vote because I didn't know what Futuyma's "view of evolution" was; I just assumed that (whatever his personal opinions) he tried to review the field fairly, including legitimate controversies, in his text books.
"the only genuine professional evolutionary biologist of the 3"
What is that supposed to mean? Collector of primary data instead of "just" theorizing? Even Dawkins (whose job is to write popular books) has actually published some real experiments.
I wonder how different the views of Dawkins and Futuyma really are (Gould revelled in the role of iconoclast and really did push some different stuff). I'd urge people to actually read Dawkins (The Ancestor's Tale is a pretty good summary of his earlier ideas, plus much more) rather than take Dr. Moran's word for it. Of course the path of evolution depends strongly on what mutations occur when--I sincerely doubt Dawkins would argue with that statement. But I could be projecting.
The best feature of this poll was that it led some of us to read about Futuyma. I abstained from voting until I had read up on him (through summaries only, I admit.)
ReplyDeleteI could tell that you were trying to lead people to vote for him, but I needed to figure out why. It makes sense from my lay perspective, any way.
To me, the controversy within evolution over which method accounts for the major forces of evolution also illustrates the frustration that I have with the prominence of Creationism/ID in the United States.
I would welcome "teaching the controversy" if indeed it meant teaching the strengths and weaknesses of the various means of evolution. I think we would all be smarter if that were the case.
Dawkins has been a (very good and very effective) popularizer rather than a research scientist most of his career, after an undistinguished start as an ethologist, and his "professional" books on evolutionary theory are largely derivative (of Williams). Gould was a distinguished invert paleontologist but colleagues with real depth of knowledge in evolutionary genetics were largely unimpressed by his more general theorizing. And he was capable of writing books that are just embarrassingly bad, like Wonderful Life (even though interpreting the Burgess Shale fossils should have been more or less within his actual professional competence.)
ReplyDeleteSven DiMilo says,
ReplyDeleteI'd urge people to actually read Dawkins (The Ancestor's Tale is a pretty good summary of his earlier ideas, plus much more) rather than take Dr. Moran's word for it.
This is wise advice. These are complex ideas. They concern the way that different scientists look at evolution (i.e., their worldview). The very nature of the dispute means that proponents of one side or the other will often have great difficulty recognizing why their views are so upsetting to the other side.
The adaptationists are often quite bewildered by the whole thing. They can't see why they are being criticized. I'm sure the pluralists suffer from the same sense of bewilderment whenever anyone attacks their position.
Of course the path of evolution depends strongly on what mutations occur when--I sincerely doubt Dawkins would argue with that statement.
The essence of Dawkins' argument is that living things will always adapt to their environment. If the gazelle needs to run faster to escape the lion then that adaptation will occur. If a tree needs to grow taller, then it will.
Dawkins always assumes that the required mutations will be available whenever they are needed. Furthermore, he tends to imply that most species are almost perfectly adapted to their present environment and that can only happen if mutations are not limiting.
Read this quotation from The Blind Watchmaker and decide for yourself whether mutations play a role in the Dawkins' version of evolution.
If the conditions in which a lineage of animals lives remain constant; say it is dry and hot and has been so without a break for 100 generations, evolution in that lineage is likely to come to a halt, at least as far as adaptations to temperature and humidity are concerned. The animals will become as well fitted as they can to the local conditions. This doesn't mean that they couldn't be completely redesigned to be even better. It does mean that they can't improve themselves by any small (and therefore likely) evolutionary step .... Evolution will come to a standstill until something in the conditions changes: the onset of an ice age, a change in the average rainfall of the area, a shift in the prevailing wind.
I'm unconcerned about these types of disputes or who's right, since ultimately none of the participants would deny the facts once they became known. Each is trying to advance their best understanding, and each (including Gould if he were still with us) would shake the others' hands warmly if they came up with a better theory.
ReplyDeleteI see no point in putting down a particular view such as Dawkins'. These are false controversies since they have all contributed to human knowledge and the rightness or wrongness of their theories will resolve themselves naturally in time. There's no need to set up "camps" within science. They're all on the same team.
Steve LaBonne says,
ReplyDeleteDawkins has been a (very good and very effective) popularizer rather than a research scientist most of his career, after an undistinguished start as an ethologist, and his "professional" books on evolutionary theory are largely derivative (of Williams).
I fear your bigotry is showing. You have shifted the goalposts from saying that Dawkins is not a professional evolutionary biologist to saying that he is not a research scientist.
I suspect you're one of those people who think that all legitimate research scientists have to work at the bench in order to qualify. I strongly disagree with that point of view. I don't think we have enough theoreticians around and I do not denigrate those who spend most of their time at it.
Dawkins has made valuable contributions to evolutionary theory.
Gould was a distinguished invert paleontologist but colleagues with real depth of knowledge in evolutionary genetics were largely unimpressed by his more general theorizing.
Gould was not a geneticist by any stretch of the imagination so why should we care what they think? There are lots of very intelligent people who disagree with Gould but does that eliminate Gould from the ranks of genuine professional evolutionary biologists? I don't think so. And neither do the people who write textbooks on evolutionary biology.
And he was capable of writing books that are just embarrassingly bad, like Wonderful Life (even though interpreting the Burgess Shale fossils should have been more or less within his actual professional competence.)
Ah, yes. You've been reading too much Dennett! It's not good for you. The adaptationists have done an excellent job of misrepresenting everything in Wondeful Life. I still think it's one of Gould's best books.
I hope your not one of those silly people who think that Gould didn't understand what a phylum was. Are you?
Maybe if Futuyma wrote popular science books he'd be more popular. I voted for Gould for nostalgic reasons, his interviews with Peter Szowski [sp?] so many years ago were what turned me on to biology, and because he was one of the last truly great American public intellectuals. Now that Sontag is dead I don't think there are any left.
ReplyDeleteI was one of those who voted on the side of Gould (and I also liked Wonderful Life very much), but I'm also glad to see that the conclusion is that all of the good evolutionary biologists, including Futuyma and Dawkins, have made and are making real contributions. One concept that's really hard to get across to people is that this isn't a race where at the end we'll announce that Professor X was the winner, and he was completely right in all things -- we are always aspiring to a (dare I say it) synthesis of the best of many contributions.
ReplyDeleteThe poll needed to throw in more Lewontin and Raff and Oyama, though. Evo- and eco-devo aren't in this snapshot of a synthesis! (Gould, at least, was a developmental biology sympathizer.)
I'm getting tired of the role of Dawkins's bulldog around here (I really don't agree with him about everything!), but...I see nothing whatsoever controversial about the quote Dr. Moran provides, with the possible exception of specifying 100 generations as enough time. (In fact, he is explicit in that passage that adaptation is not perfection.) If the objection is the assumption that all possible (or at least "easy") beneficial mutations will eventually occur, I suspect there exist empirical data on mutation rates that could be brought to bear. In fact, I seem to remember Dawkins bringing such data to bear.
ReplyDeleteAs for dismissing Dawkins as "not a genuine professional evolutionary biologist" because his ideas are derivative of G.C. Williams (one could certainly do worse!), I guess I'll ask: Futuyma's original ideas are...?
Gould was not a geneticist by any stretch of the imagination so why should we care what they think? Oh, I dunno, maybe the fact that evolution is about change of GENE frequencies in populations?
ReplyDeleteAs to Dawkins, virtually everything in The Selfish Gene is directly derivative of Williams. There is some more original thinking in The Extended Phenotype, but I don't think there are too many serious evolutionary biologists who regard it as a major contribution.
I am uninterested in silly gotcha games, and therefore in goalposts shifted or unshifted.
I admire Dawkins greatly, by the way- he is a superb and indispensable popularizer. I have no intent to downgrade the importance of that, quite the contrary.
ReplyDeleteRead this quotation from The Blind Watchmaker and decide for yourself whether mutations play a role in the Dawkins' version of evolution.
ReplyDelete"If the conditions in which a lineage of animals lives remain constant; say it is dry and hot and has been so without a break for 100 generations, evolution in that lineage is likely to come to a halt, at least as far as adaptations to temperature and humidity are concerned. The animals will become as well fitted as they can to the local conditions. This doesn't mean that they couldn't be completely redesigned to be even better. It does mean that they can't improve themselves by any small (and therefore likely) evolutionary step .... Evolution will come to a standstill until something in the conditions changes: the onset of an ice age, a change in the average rainfall of the area, a shift in the prevailing wind."
I'm certainly not an expert in evolutionary biology, but let me tell you how I see it and you can tell me where I'm going wrong.
I must say that I don't see the problem with the passage from Dawkins that you quoted - of course Dawkins is saying that mutation plays a role in evolution! How else would the 100 generations of improvement have occurred?
Here's how I understand things: evolution acts on existing variation within a population. The biggest evolutionary gains are made soon after an environmental change occurs as the most favourable variations in the existing population are selected for (think Galapagos finches as studies by the Grants). Later on, as the population becomes narrower in variation for a particular trait, we become increasingly reliant upon mutations to provide enough variation for selection to act on. Note: this does not imply that drift cannot be occurring as well.
It seems to me that all Dawkins is saying in the above extract is that there is a limit to the efficiency gains that are possible through evolution, after which time any mutations will tend to push in the 'wrong' direction i.e. mutations to the genes in question become increasingly likely to be deleterious as a local fitness peak is approached. Hence, improvement in regard to the trait in question slows through the generations and eventually stops - if you move off a peak, the only way is down.
What's the problem with that? Seriously, please enlighten me; I'm only an undergrad biology student, but I'm very interested in learning more about evolutionary biology.
Ian B Gibson asks,
ReplyDeleteI must say that I don't see the problem with the passage from Dawkins that you quoted - of course Dawkins is saying that mutation plays a role in evolution! How else would the 100 generations of improvement have occurred?
Of course mutations occurred. That's not the point. What we're discussing is the difference between Dawkins' view and that of mutationism, which he strongly opposes.
According to Dawkins, all mutations will be available when needed. That's why the organism can reach a state of "as well fitted as they can to the local conditions." That's why, according to Dawkins, evolution can come to a halt when this happens.
Mutationist would argue that the direction of evolution can be very much determined by the type of mutations that happen to arise at a given moment. They would argue that organisms can rarely become perfectly adapted to their environment because some of the required mutations might not happen.
Mutationists are usually pluralists as well so, of course, they would hold to the position that evolution can never stop because raandom genetic drift of nearly neutral mutations is occurring all the time. A pluralist could never possibly make the statement that Dawkins' made in The Blind Watchmaker because they believe that evolution can never stop.
When Steve LaBonne claimed that "evolutionary geneticists" didn't think much of Gould's ideas I aske d why we should care what they think.
ReplyDeleteSteve replied, "Oh, I dunno, maybe the fact that evolution is about change of GENE frequencies in populations?"
Gould's area of expertise was macroevolution. He wanted to extend evolutionary theory beyond population genetics to include higher level mechanisms like species sorting. I see no reason to believe that "evolutionary geneticists" would be especially competent to judge his contributions to macroevolutionary theory. On the other hand, I can see why they might feel threatened by an attempt to restrict their area of expertise. Perhaps that's why they don't like Gould?
Steve, have you read The Structure of Evolutionary Theory? There's no genetics there. Gould is relatively unconcerned with whether allele frequencies change by natural selection or random genetic drift.
The problem with ruminations about higher-level selection is precisely that their feasibility (and possible mechanisms) at the genetic level is never demonstrated by their proponents. Sober and Wilson perceived and tried to fill this void but not very convincingly. Also, as you know there are virtually always alternative explanations for any phenomenon claimed to be the result of higher-level selection, and proponents like Gould never really have done much of a job of explaining how to test the alternative explanations, let alone actually do so. (Admittedly that is probably intrinsically difficult to do in most cases.)
ReplyDeleteI have paged through that baggy monster but I don't have the desire or patience to really read it. I've seen enough to realize that Gould while stimulating is also both confused and confusing, as ever. I make no claim that this is anything more than a matter of taste.
I picked Futuyma on the basis of what I knew of his view of evolution...I'd be happy with my answer even if Futuyma hadn't been the "correct" answer. That said, reading the question it seemed pretty clear to me that Futuyma was Larry's choice. Dawkins and Gould are most famous for being famous. "Writing a pretty decent textbook" just doesn't put you in the same category. In a sense, Futuyma seemed the odd man out among the choices.
ReplyDelete"I make no claim that this is anything more than a matter of taste."
ReplyDeleteI think you are correct in saying this Steve, as it is fairly obvious from your post that you are confusing streams of evolutionary research.
It all comes down to scale. Gould's work as a paleontologist interested in developmental constraints and deep time is a macro view of evolution. Genetics on the other hand is a microview of evolution. Field based observations are somewhere in between.
Each approach is perfectly valid in exploring the evolution of life on this planet, but there are very few proponents who can skilfully combine all branches of evolutionary science into their lab's research. However each stream has something to offer the other in terms of the bigger picture.
I note that Ernst Mayr wasn't in the list either.
I too don't really see the problem with that quote from Dawkins, bearing in mind that it's from a popular science book.
ReplyDeleteAs such the "100 generations" is clearly a figure of speech. What he means is "sufficient time to reach an equilibrium situation". I guess the mutationist argument is that some mutations are sufficiently infrequent that you never reach an equilibrium. But then how does that differ from Dawkins' own get-out clause?
"This doesn't mean that they couldn't be completely redesigned to be even better. It does mean that they can't improve themselves by any small (and therefore likely) evolutionary step"
That is - if a mutation is unlikely enough, it won't be available for selection. So the whole paragraph in fact has an intrinsic predicate that organisms will become as well adapted as possible given limited mutation rates. So where's the problem?
The larger problem I see with the communication of evolutionary ideas to the public is that the definition of "fitness" is insufficiently well understood. Evolution will optimise for increased offspring, whether or not that can be said to be "better" according to other criteria. All sorts of "bad" phenotypes are effectively selectively neutral.
This of course is also the problem with the cariacature adaptationist view.
The more I've learnt about these arguments over the past six years, the more trivial and pointless they seem. They are mostly historical. Dawkins acknowledges genetic drift and puctuated equilibrium, while Gould acknowledged the limited application of punctuated equilibrium, and Futuyama acknowledges that natural selection is more important than drift for producing the phenotypes that Dawkins finds interesting.
ReplyDeleteIt's a case of one party saying "Yes, your ideas are relevant, but these are more important/interesting," and the other party saying "Yes, your ideas are important/interesting, but don't forget that these ideas are relevant."
Criticising Dawkins for not devoting more time to drift reminds me of the reviewers of Enemies of Reason who criticised the programme for not discussing the bad things that pharmaceutical companies do. Pharma simply didn't come under the programme remit, just as drift doesn't play a major part in the aspects of biology that Dawkins is interested in. He's not denying that there's a story in them, it's just not the story he's telling.
Damn, it seems one has to spellcheck one's comments before publishing them on this software!
ReplyDeleteJoe, that's exactly what I've been saying for years now whenever Larry voices that objection to Dawkins's books. For reasons of both pedagogical strategy (as with the eye passage in Darwin, he wants to show that what his audience perceives as the "hard cases" can be successfully explained) and personal interest, he deals mainly with what one might call cases of "extreme" adaptation (as in the bat echolocation systems described in such loving detail in TBW). The consensus, quite explicitly shared by Dawkins, is that such instances of "good design" are not a general feature of evolution but occur in a quite specific evolutionary scenario, namely arms races. So yes, a book like TBW will not give its audience a general overview of evolutionary biology- it's a very partial view. But in my opinion it remains as good a place to start a newbie as there is. It's just that they shouldn't stop there.
ReplyDeleteI've read most of Dawkins books and didn't see him assuming "the required mutations will be available whenever they are needed". And Dawkins is very interested in macroevolution; nearly all what he writes is about macroevolutionary changes. What is the "problem"? He explains macroevolution in a way that is rather close to standard, mainstream or "orthodox" (if you prefer) theory. But that doesn't mean lack of interest.
ReplyDeleteI voted for Futuyma and also like Gould views. But think you are caricaturizing Dawkin's
I realy can`t understand all that hostility to Dawkins today i have read one essay by Dawkins on A Devil´s Chaplain that would be interested to your assertion of Dawkins strict adaptionism the essay is called "Darwin Triumphant" pag 78 (hardcover).After reading his latest books i m sure that Dawkins is not a strict adpationist
ReplyDeleteWhen your school board chairman says that he wants to "teach the controversy", point him to this article and say "THIS is where the real evolutionary controversy lies."
ReplyDeleteMartinDH
Dawkins (my emphasis):
ReplyDelete"...evolution in that lineage is likely to come to a halt, at least as far as adaptations to temperature and humidity are concerned."
Moran (my emphasis):
"Mutationists...hold to the position that evolution can never stop because raandom genetic drift of nearly neutral mutations is occurring all the time. A pluralist could never possibly make the statement that Dawkins' made in The Blind Watchmaker because they believe that evolution can never stop."
Spot the difference? Spot the strawman? This gets tiresome.
And what the hell is a "mutationist"?
I think that's not a good definition for mutationists. Mutationists believed that mutation is the main source for discontinuity between taxons and the cause of evolutionary novelties and adaptations. For mutationists, mutation is the "creative" force in evolution. For selectionists, it is selection.
ReplyDeleteSven, you answered your own question there. Dawkins (in that quote) is arguing that evolution has stopped as far as temperature regulation is concerned. In this instance he is discussing evolution as it relates to adaptations to environment.
ReplyDeleteA 'mutationist', on the other hand, does not see evolution stopping at all. Mutations accrue all the time. Some mutations may be favoured according to environment (selection), some are negative (selection), others may have no negative or positive effect (neutral). 'Evolution' from a mutationist's point of view has not stopped at all in temperature regulation alleles because mutations are still accruing.
Genome and haplotype mapping will go some of the way into addressing how much weight should be given to either camp.
True...Mayr was a more infuential synthesis representative than futuyma...I like Mayr. Not all scientists have that philosophical awareness.
ReplyDeleteI marked Gould, but Gould, like all others on the list, basically chickened out from the entire topic of the relevance of epigenetic change for adaptation and evolution. Bad. Very bad. Shame on them three!
West-Eberhardt does not dodge the epigenetic topic and has received good attention, but the fact she wants to make a still fundamentally orthodox heterodoxy results in a contradictory and bizantine confusion...in a nevertheless still very challengig, and indispensable piece of work. Evereybody should have it. It is very phenomenological, providing interesting biological data throughout that WILL challenge your theoretical preconceptions.
Sanders: "Gould, like all others on the list, basically chickened out from the entire topic of the relevance of epigenetic change for adaptation and evolution. Bad. Very bad. Shame on them three!"
ReplyDelete"the fact she (West-Eberhard) wants to make a still fundamentally orthodox heterodoxy results in a contradictory and bizantine confusion."
Please, Sanders, enlighten us on how we ought to think about evolution.
Sanders (from the 'Dennet on Adaptationism' thread, corrected for spelling and grammar):
http://sandwalk.blogspot.com/2007/08/dennett-on-adaptationism.html
"Nor do complex adaptations constitute in themselves evidence for selection shaping an adaptation."
"(A) few mutations with large effect are behind the origin of new adaptations. In fact, there is no example that I know of where an adaptation has been shown to be have been shaped by and accumulation of several genes by natural selection."
"Please, Sanders, enlighten us on how we ought to think about evolution".
ReplyDeleteWhat do I look like, freakin santa claus?
I'm not feeeling generous today, specially towards adaptationists who can't really follow ideas. You'll just have to think for your own self, which is what I do.
To demand a field example of an adpataion shaped by directional selection is a perfectly honest demand. Why not just provide it instead of playing flabbergasted by such heresy? I am completely open to the possibility there are such cases. So, provide them.
If you show generosity and provide me with such a case that I may reflect upon, we may find something interesting to talk about...
ReplyDeleteSven DiMilo, you would be wise to ponder the following statement by Stephen J. Gould in his seminal 1982 Science paper "Darwinism and the Expansion of Evolutionary Theory",
ReplyDeleteThe world is not inhabited exclusively by fools, and when a subject arouses intense interest and debate, as this one has, something other than semantics is usually at stake.
In this case the "something" is the big picture view of evolution or one's "model" of how evolution occurs. Some people may call this their worldview or paradigm.
I suggest you stop looking for trivial ways of dismissing those who disagree with you and start trying to understand what they are saying.
If you don't understand what mutationism is then I suggest you go back and read the strawman version that Dawkins attacks in The Blind Watchmaker (p. 305) and then look at the modern version I outline in Evolution by Accident.
I think that for the sake of clarity Larry would be better off using Masatoshi Nei's term "neo-mutationism", to avoid confusion of this viewpoint with the early-20th-century likes of DeVries.
ReplyDeleteBy the way here is a nice summary of that viewpoint- the abstract of a recent PNAS review article by Nei.
ReplyDeletehttp://tinyurl.com/2j4bnj
Recent studies of developmental biology have shown that the genes controlling phenotypic characters expressed in the early stage of development are highly conserved and that recent evolutionary changes have occurred primarily in the characters expressed in later stages of development. Even the genes controlling the latter characters are generally conserved, but there is a large component of neutral or nearly neutral genetic variation within and between closely related species. Phenotypic evolution occurs primarily by mutation of genes that interact with one another in the developmental process. The enormous amount of phenotypic diversity among different phyla or classes of organisms is a product of accumulation of novel mutations and their conservation that have facilitated adaptation to different environments. Novel mutations may be incorporated into the genome by natural selection (elimination of preexisting genotypes) or by random processes such as genetic and genomic drift. However, once the mutations are incorporated into the genome, they may generate developmental constraints that will affect the future direction of phenotypic evolution. It appears that the driving force of phenotypic evolution is mutation, and natural selection is of secondary importance.
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ReplyDeleteThanks for the review Larry and triggering an informative discussion. It seems that I know less about Futyuma than I should.
ReplyDeleteI suspect you're one of those people who think that all legitimate research scientists have to work at the bench in order to qualify. I strongly disagree with that point of view. I don't think we have enough theoreticians around and I do not denigrate those who spend most of their time at it.
ReplyDeleteI can't speak for Steve, but, being one of those theoreticians myself who use data rather than create it in the lab, I realize that it is still required to actively perform research in order to be considered a research scientist, theoretical or no. Dawkins hasn't published peer reviewed research for decades. He's an ex-scientist turned science writer turned atheism writer, who just so happens to be an zoology professor besides. There's nothing wrong with any of that, any more than there is with abandoning research to teach full time, of course, but being a research scientist means one *does scientific research*.
That being said, there are and have been real research scientists in evolution who publish popular works -- Sean Carroll, for example, or if you want a theoretician, the late John Maynard Smith.
Informative. Especially Joe Dunckley et al managed to broaden the perspective.
ReplyDeleteAs Mike Haubrich, I had to read summaries of Futuyma, liked what I saw and despite indications that this should be the preferred choice voted for him. :-P
Here's a story about an abusive Christian cult - in Canada
ReplyDeleteI agree completely with what Jonathan said.
ReplyDeleteI use a different definition of scientific research. It includes the research you have to do to develop a new theory. For example, in my opinion Gould did a lot of scientific research in order to produce his book The Structure of Evolutionary Theory. Most of this research was finding and reading the scientific literature and putting it into some sort of coherent context.
ReplyDeleteJonathan and Steve seem to have in mind a definition of research that requires you to create data rather than just analyze it. By that definition, graduate students in English, History, and Political Science would hardly ever be doing research. (Please, avoid the temptation to make up data creation projects in each of these fields. I think you get the point.)
I don't understand why it's so important to point out that Dawkins is not a "researcher" or a "genuine professional evolutionary biologist." Does that make his ideas less worthy?
Jonathan and Steve seem to have in mind a definition of research that requires you to create data rather than just analyze it.
ReplyDeleteNo. Please for goodness' sake read what Jonathan actually said. Of course data analysis can be research- rigorous data analysis subjected to peer review. What people like Nei do, for example.
I don't understand why it's so important to point out that Dawkins is not a "researcher" or a "genuine professional evolutionary biologist." Does that make his ideas less worthy?
ReplyDeleteIt points up the absurdity of your constant use of him as a straw man, especially when you try to analyze the (necessarily and appropriately) simplified presentations of ideas in his popularizations as though they were rigorous professional statements of research results. As well as pointing up the silliness of that poll.
Jonathan and Steve seem to have in mind a definition of research that requires you to create data rather than just analyze it.
ReplyDeleteLarry, as I wrote, *all I do* is analyze data. Of course I don't "have in mind a definition of research that requires you to create data rather than just analyze it".
I don't understand why it's so important to point out that Dawkins is not a "researcher" or a "genuine professional evolutionary biologist." Does that make his ideas less worthy?
It means that his (scientific) ideas are at best popularizations of the research of others and not really "his". Even his most famous work, "The Selfish Gene", is not original research. His opinions on science may be interesting and enjoyable to read, but no more so than those of other science writers such as Jonathan Weiner or Carl Zimmer (both of whom I incidentally consider to be better science writers.)
I strongly suspect that part of the reason why Dawkins' books sell more than those of arguably better science writers is that the much of the public mistakenly thinks that he *is* an active researcher (perhaps even a great, Nobel-class one) and that by reading his books one is getting cutting edge science "straight from the horse's mouth". But it isn't so.
@Dr. Moran: "If you don't understand what mutationism is then I suggest you go back and read the strawman version that Dawkins attacks in The Blind Watchmaker (p. 305) and then look at the modern version I outline in Evolution by Accident."
ReplyDeleteI have done as you suggest, and I appreciate the information. I was unfamiliar with the term. My reading of the Dawkins passage you cite is that he is arguing against a real, historical view, not a strawman of your modern version (for what it's worth, the links on the first few pages of a Google search on "mutationism" are nearly all about that discredited historical view of De Vries et al. If you are going to use an existing term in a nonstandard way, you can expect to be misunderstood pretty often).
I very much enjoyed reading your essay, which is nicely done. Again: neither me nor anyone else would argue with the point that selection can't select from nonexisting variation. Of course the random nature of mutation and the rarity of specific mutations can constrain evolution. Of course all variation, including incipient adaptations, must arise first through mutation, the "source of novelty" if you want to put it that way. Of course adaptation to the environment is seldom or never
"perfect," in part because of such constraints.
But you know what? Dawkins would agree with every word of the above too. I sincerely feel that it is you who is indulging (repeatedly, as your essay shows) in strawman caricature of his view. For example, keep on reading after p105 of The Blind Watchmaker with an open mind and you'll see what I mean. On pp309-310 he even sets up a dialogue between a "real-life Darwinian" and an "extreme caricature of a Darwinian," and the words of the caricature are very similar to what you claim are Dawkins's views. Just one quote (from the real-life conversant) of several that make my point:
"I wonder why [x didn't evolve--it doesn't matter what]...I suppose one answer might be that mutation never provided the necessary variation."
The chapter goes on to discuss developmental constraints of the you-can't-get-there-from-here variety (he emphatically agrees they are important). There is a whole chapter of The Extended Phenotype called "constraints on perfection."
The guy just simply does not believe the stuff you keep claiming he believes (or, more weaselly, what you claim he "implies"). And neither do I.
@Dr. Moran: "I suggest you stop looking for trivial ways of dismissing those who disagree with you and start trying to understand what they are saying."
You know, I really am trying to understand what you (and even unpleasant people like sanders) are saying. The problem is that I am limited to what you have actually written. To wit:
Dawkins sez that in a long-time constant environment, evolution of adaptation to that environment will eventually slow to a stop (note that he does not say or imply that this means the population is perfectly adapted; explicitly the opposite, in fact).
You reply (and I quote directly to be sure to get it right):
"Mutationists...hold to the position that evolution can never stop because raandom genetic drift of nearly neutral mutations is occurring all the time. A pluralist could never possibly make the statement that Dawkins' made...because they believe that evolution can never stop."
You are explicit here that you disagree because he is ignoring "random genetic drift of nealy neutral mutations."
My point (and I acknowledge I could have made it less snarkily; I apologize) was simply that adaptation (what Dawkins was explicitly talking about) cannot result from drift (what you were explicitly talking about), and that random drift cannot produce adaptation. By definition.
That point is far--far!--from "trivial" or "semantic." I think it is you, not me, who is misunderstanding here (and for my part in fostering misunderstanding, I again apologize).
If your major point is that random drift of (near) neutral traits can and does occur, nobody--not me, not Richard Dawkins--is disagreeing. If you think that mutation rates in large populations are often insufficient to drive adaptation that could otherwise occur, I ask for your evidence. When asked before, you have offered only personal incredulity.
Adaptation is empirical; some of the best, most clear examples are in your own field of biochemistry (Hochachka and Somero). But that is emphatically NOT the same statement as "all populations are perfectly adapted to their environments because all possible mutations occur often enough."
Nobody. Thinks. That. Not me. Not Richard Dawkins or any other "adaptationist." We are all pluralists and it's time you stopped insisting otherwise. IMHO.
I do agree that this is all about worldview and paradigm. Mine is based on knowledge of organisms (animals, as it happens) living in more-or-less natural environments (including the Mojave Desert, as it happens). People like Nei and Kimura are coming from sequence-level molecular genetics. That's a difference of several levels of organization. One of the quotes from Nei's book in your essay makes reference to his applying neutral theory to phenotypic evolution, and I thank you for bringing that to my attention--I'm going to track it down.
In the meantime, I also thank you for prompting me to pull The Blind Watchmaker back off the shelf after many years. While leafing through I found this relevant quote, with which I agree, and with which i suspect you disagree (and I'd be interested to know why):
"Of course, large quantities of evolutionary change may be non-adaptive, in which case these alternative theories [neutralism, mutationism] may well be important in parts of evolution, but only in the boring parts of evolution, not the parts concerned with what is special about life as opposed to non-life."
"Of course, large quantities of evolutionary change may be non-adaptive, in which case these alternative theories [neutralism, mutationism] may well be important in parts of evolution, but only in the boring parts of evolution, not the parts concerned with what is special about life as opposed to non-life."
ReplyDeleteBoring becuase it's not selection?
What dumbasses
I think the biggest problem Dawkins and his followers have is that they have cero capacity to tell when they are just rocking their wooden horse.
ReplyDeleteThey clealry think it's genius.
Sanders, if West-Eberhard and Gould are inadequate, what do you think of these theorists (if you are familiar with them(?)): Mae-Wan Ho, Stanley Salthe, A. Lima-de-Faria. Are you capable of naming any evolutionary scientists who you believe are courageously addressing the important issues without confusion?
ReplyDeleteI'm not familiar with those.
ReplyDeleteThere is plenty of smart people and if someone asks me which approach to biology I find is the most elegant, I would say look into systems theory. There are a lot of great names there.
Though systems theory has a greater presence in the social sciences, there have been advances in biology, see Stuart Kauffman; Maturana & Varela; Susan Oyama. Margulis has also talked of this, I think.
The GOOD things is, systems theory in biology is still in its diapers; There remains LOTS to be done. Plus I can hardly say that I agree with everything the people I mention above have said; they do not conform a homogeneous school of thinking, presenting important differences.
Of course there will be confusion...as there usually is in times of scientific transition. The days of complete clarity of the "modern synthesis" are INDEED over. For good!
ReplyDelete"Boring becuase it's not selection?"
ReplyDeleteNo. Boring because it seems it doesn't produce adaptation. Organs. Insticts. The bird's respiratory system, the human brain, the bee's language, the octopus eye, the bacterial flagellum... Lots of beautiful macroevolutionary things :o)
The GOOD things is, systems theory in biology is still in its diapers; There remains LOTS to be done. Such as producing anything of scientific value. ;)
ReplyDeleteThis baloney has been going on for quite a few years now (so why is it still in diapers? Shouldn't it finally learn to use the potty one of these days?), and what exactly has it accomplished by way of solid results? It looks more like new-age religion than like science.
No, Sanders, not "boring because it's not selection," you obstinate jerk. "Boring" (and I know that's a provocative term, which is why I used it) because, by definition, such traits have nothing to do with survival and reproduction of organisms in natural environments. Life, in other words; you know, the subject of Biology?
ReplyDeleteAnd now this "retarded" "dumbass" is signing off for good. Have a pluralistic day!
Sven DiMilo says,
ReplyDeleteBut you know what? Dawkins would agree with every word of the above too. I sincerely feel that it is you who is indulging (repeatedly, as your essay shows) in strawman caricature of his view.
No, actually he doesn't agree. Dawkins has read my essay and we have discussed it quite a bit.
I mean. On pp309-310 he even sets up a dialogue between a "real-life Darwinian" and an "extreme caricature of a Darwinian," and the words of the caricature are very similar to what you claim are Dawkins's views.
This is the famous "angels" passage that has been extensively analyzed. Dawkins is arguing that some things just aren't possible—like wings on your back—because the required variation will never appear.
That's something we can all agree on. What I'm arguing is that even when an adaptation is possible it doesn't always happen because the required mutation doesn't arise at the right time or, if it does, it is lost before it can be fixed in the population.
Dawkins believes that most organisms will find a way to the top of Mt. Improbable. I believe that, in many cases, they won't.
If your major point is that random drift of (near) neutral traits can and does occur, nobody--not me, not Richard Dawkins--is disagreeing.
This is correct on one level but it's not correct on another. I'm well aware of the fact that Dawkins pays lip service to random genetic drift. There are numerous passages in his book where he refers to drift as one of the mechanisms of evolution. However, he relegates it to the molecular level where it is unimportant to Dawkins.
The point that's contentious is whether visible features are all due to adaptation. Dawkins takes the position that they are—with minor exceptions—and the pluralists take the position that random genetic drift can apply to visible phenotypes as well.
What this means is that Dawkins is able to discuss the extremely long fingers of the aye-aye and make the following claim with a straight face,
... we may be sure those fingers are long for a good reason: aye-ayes with shorter fingers would be penalized by natural selection, even if we don't know why. Natural selection is a strong enough theory to be predictive in this fashion, now that science no longer need convincing of its truth. (The Ancestor's Tale p. 140)
A pluralist could never make such a statement. A pluralist would wonder—among other things—whether the long fingers are a maladaptation and the whether the aye-aye is on its way to extinction.
In the meantime, I also thank you for prompting me to pull The Blind Watchmaker back off the shelf after many years. While leafing through I found this relevant quote, with which I agree, and with which i suspect you disagree (and I'd be interested to know why):
"Of course, large quantities of evolutionary change may be non-adaptive, in which case these alternative theories [neutralism, mutationism] may well be important in parts of evolution, but only in the boring parts of evolution, not the parts concerned with what is special about life as opposed to non-life."
The quotation is from page 303. I most emphatically disagree. My main interest is molecular evolution and that's mostly concerned with non-adaptive evolution. One of the things that puzzles me is why there's so much junk DNA in our genome. It would be extremely foolish to argue that this is a boring topic.
I'm also interested in explaining the visible effects of evolution and part of that explanation, in my world, involves consideration of non-adaptive possibilities. I think it's dead wrong to rule those possibilities out of order simply because you might find the explanation boring.
Dawkins disagrees. He thinks that random genetic drift only happens at the molecular level. For example, on the very page (p. 304) he says,
As far as we are concerned, a neutral mutation might as well not exist because neither we, not natural selection, can see it. A neutral mutation isn't a mutation at all, when we are thinking about legs and wings and eyes and behaviour!
There are lots of similar statements in Dawkins' books. It's clear in his mind that every visible phenotype is subject to natural selection.
On the other hand, one can't quibble with the last part of Dawkins statement on page 303. He defines the important feature of life that distinguishes it from non-life as "adaptive complexity." By definition, random genetic drift is ruled out.
Dr. Moran: Thank you for your reasoned response. Like you said, differences in worldviews.
ReplyDeleteReally can't add anything except to say: good discussion, all. Nice to see some somewhat more substantial discussion of these divergences on the interwebs. Like MartinDH said, if you really want to 'teach the controversy', this is one actually worth talking about.
ReplyDelete(Oh... and I'm not just trying to make everyone happy, but actually, though I'm pretty sure I voted, I can't quite remember how I decided to go at the time... Much as I get that there are real consequences to getting the biology right, here, puzzling out to what degree selective pressures and random drift in the absence thereof shape evolution, I've never been real partisan on this. Reading how Larry describes it, I do have some fondness for Futyama's position, now, though.)
"On the other hand, one can't quibble with the last part of Dawkins statement on page 303. He defines the important feature of life that distinguishes it from non-life as "adaptive complexity." By definition, random genetic drift is ruled out"
ReplyDeleteWhy not? neutral traits (spandrels, for instance) can become thereafter part of a complex adaptation. Other non-selective processes, such as exaptation, are behind the evolution of almost every complex adaptation.
But try to explain this to the ideologoues of adapationism. They think this is juts a matter of pinting to any complex adaptation (Organs. Insticts. The bird's respiratory system, the human brain, the bee's language, the octopus eye, the bacterial flagellum, yeah, that's right, pretty much everything) and say "natural selection". Pretty cheap. Anyone can be an evolutionary biologist like that, huh.
It IS retarded, specially taking into account that they seem to have ony examples of macroevolution as examples of the role of selection in shaping complex adaptation. Is that their "evidence"? Mayr and Gould were very explicit about not making this foolish mistake. Secially Gould, since he introduced exptation. Ever heard of this, adapto-maniacs?
I should not need to explain whythat is wrong; I have already mentioned exaptation, and spandrels. Anyone who has actually looked into actual avaialbale about the macroevolution of a complex adaptation will find that there hardly ever is a story of directional selction for current use behind it; it is usualy history of refutation of simplistic selectionism and without exaptation, you're going nowhere. But it seem to me that noone here is showing any true understanding of exapataion.
How about some actual neato documenttion of the process itself of directiona selection shaping a complex adpataion, you know, in the field, at the microevolutionary level? I'd love one of those.
Exaptation is a "non-selective process"? Are you sure?
ReplyDeletein fact, a field example of the shaping of just any adaptatation by directional selection would be nice. Not necessarily a complex one.
ReplyDeleteIt's obvious. When a structure happens to become useful for a completely different function: that happy coincidence is not selection. It's like sayig that if you can hold a window open with a screwdriver is an excellent example of selection. maybe for you guys it is, but some of us have "limits", you know .
ReplyDelete"A pluralist would wonder—among other things—whether the long fingers are a maladaptation and the whether the aye-aye is on its way to extinction."
ReplyDeleteSometimes non-biology, non-paleontology people, when they see a giant bodied dinosaur, an ultra-long necked fossil reptile, or one with enormous claws, or teeth, or dorsal sail, or horns, or spikes... they make the same comment: "maybe that was a disfunctional feature, so the species became extinct". Now I understand: they are pluralists!
PD: The aye-aye is on extinction risk. I think pluralists are in fact reasonable people and they won't blame the critter's long fingers ;o)
"When a structure happens to become useful for a completely different function: that happy coincidence is not selection."
ReplyDeleteOf course. But exaptations are suposed to be more complex processes, aren't they? Or are they just "happy coincidences"? You have a coat of hairy protofeathers that keep you warm and then, one morning... Wow!! What a coincidence! I can fly with them!
yes, coincidences work instantaneously; but your feather case is not a true example. I'm sure you are smarter than that.
ReplyDeleteAre you seriously reducing the process to a mere "coincidence"?
ReplyDeleteIt seems you have an strange, and simplistic, concept of exaptation. Not very pluralistic.
No. That would be as stupid as reducing adaptation only to selection, right? Plus, we have development an epigenesis to consider too.
ReplyDeleteI will say, of course that the coincidence is a required component of exaptation; but the ambivalence of function is usually precede by structural iteration or funtionally redundant structures.
ReplyDeleteIs all that selection, too? haha
"No. That would be as stupid as reducing adaptation only to selection, right?"
ReplyDeleteMaybe, or maybe not. In general, adaptation can be explained without genetic drift (for example), but it can't be explained through genetic drift. Also, it can be explained through natural selection, but not without natural selection. And it is not obvious that "reducing" adaptation to selection implies the exclusion of exaptations (a kind of adaptation) or the exclusion of mutations, epigenesis, "development", etc. This is arguable, but my poor English is reaching its limits.
So, it's normal that an author who is very interested in adaptation don't spend much time with say, drift. I suppose Dawkins thinks that the role of genetic drift and other factors can be neglected when explaining adaptive evolution. Maybe he is wrong. But I haven't read from him sentences like "adaptive evolution is a non drifting process" or "there's never been function shifts during adaptation" or "neutral traits or genes never become beneficial", nor "populations never lack every possible mutation when it is needed".
I usually read that kind of bold negations from people who describe themselves as "open minded" or "plural".
Why, that was a fascinating post. Thanks--I learned something.
ReplyDeletePaleoFreak says,
ReplyDeleteSometimes non-biology, non-paleontology people, when they see a giant bodied dinosaur, an ultra-long necked fossil reptile, or one with enormous claws, or teeth, or dorsal sail, or horns, or spikes... they make the same comment: "maybe that was a disfunctional feature, so the species became extinct". Now I understand: they are pluralists!
I don't understand. Are you saying that real biologists and real paleontologists never question these features?
Have you read Ontology and Phylogenty by the paleontologist Stephen J. Gould? The classic example is the extinct Irish Elk whose antlers grew to such an enormous size that the animal probably couldn't survive. It was perfectly acceptable to ask whether those large antlers were maladaptive.
Have you ever wondered about the adaptive significance of wisdom teeth or tonsils? Or are paleofreaks not allowed to think about such things? :-)
Many people, when they can't provide evidence for their theory, adopt the strategy of falsehood. Such is the case with many of those who have fallen victim to the propaganda of renowned evolutionists.
ReplyDeleteIf evolutionists want to end the arguments all they have to do is, get their brilliant heads together and assemble a 'simple' living cell. This should be possible, since they certainly have a very great amount of knowledge about what is inside the 'simple' cell.
After all, shouldn't all the combined Intelligence of all the worlds scientist be able the do what chance encounters with random chemicals, without a set of instructions, accomplished about 4 billion years ago,according to the evolutionists, having no intelligence at all available to help them along in their quest to become a living entity. Surely then the evolutionists scientists today should be able to make us a 'simple' cell.
If it weren't so pitiful it would be humorous, that intelligent people have swallowed the evolution mythology.
Beyond doubt, the main reason people believe in evolution is that sources they admire, say it is so. It would pay for these people to do a thorough examination of all the evidence CONTRARY to evolution that is readily available: Try answersingenesis.org. The evolutionists should honestly examine the SUPPOSED evidence 'FOR' evolution for THEMSELVES.
Build us a cell, from scratch, with the required raw material, that is with NO cell material, just the 'raw' stuff, and the argument is over. But if the scientists are unsuccessful, perhaps they should try Mother Earth's recipe, you know, the one they claim worked the first time about 4 billion years ago, so they say. All they need to do is to gather all the chemicals that we know are essential for life, pour them into a large clay pot and stir vigorously for a few billion years, and Walla, LIFE!
Oh, you don't believe the 'original' Mother Earth recipe will work? You are NOT alone, Neither do I, and MILLIONS of others!
PS: Please don't lie about the 'first life' problem, scientists are falling all over themselves to make a living cell. Many have admitted publicly that it is a monumental problem. And is many years away from happening, if ever. Logical people understand this problem and have rightly concluded that an Intelligent Designer was absolutely necessary. Think of it this way, if all the brilliant scientists on earth can't do it how on earth can anyone believe that it happened by accident?????
Oh, not the claypot copy-paste guy again.
ReplyDeleteanonymous says,
ReplyDeletePlease don't lie about the 'first life' problem, scientists are falling all over themselves to make a living cell. Many have admitted publicly that it is a monumental problem. And is many years away from happening, if ever. Logical people understand this problem and have rightly concluded that an Intelligent Designer was absolutely necessary.
I made a bunch of living cells last night. I'll send them to you if you post your name and address.
"But I haven't read from him sentences like "adaptive evolution is a non drifting process" or "there's never been function shifts during adaptation" or "neutral traits or genes never become beneficial", nor "populations never lack every possible mutation when it is needed".
ReplyDeleteNo. He just said all those things are boring and not even biology. That's all.
"Are you saying that real biologists and real paleontologists never question these features?"
ReplyDeleteI've never seen a modern paleontologist writing "maybe that thing was maladaptive and led the group to extinction". The times of orthogenesis and racial senescence are gone.
"Have you read Ontology and Phylogenty by the paleontologist Stephen J. Gould?"
Yes. Long time ago.
"It was perfectly acceptable to ask whether those large antlers were maladaptive"
You are right: it is acceptable... But maybe a bit old fashioned, scientifically speaking. Let me quote from the Gould's classic 1974 article about the Irish Elk:
"Later, Megaloceros became the ralling point for anti-darwinians; they invoked orthogenesis to deny natural selection and attributed extinction to an inadaptive trend towards inmense antlers"
and Gould's conclusion:
"The inmense antlers of _Megaloceros_ were advantageous in themselves. Its extinction may be traced to late glacial changes in climate"
"Have you ever wondered about the adaptive significance of wisdom teeth or tonsils?"
Oh! Don't paint me as an ultra-pan-selectionist or something. I'm used of explaining people that not every phenotipic trait is adaptative.
paleofreak: "The times of orthogenesis and racial senescence are gone."
ReplyDeleteTrue. But even though I am an adaptationist, let me put in a plug for Otto Schindewolf's Basic Questions in Paleontology. I read parts of it recently, and although there are some wrongheaded ideas there is a wealth of interesting material there (including the whimsical "dragon" fossil).
Plus, there may be a hint - only a hint - of truth in these older ideas, considering clade selection, evolvability, and deveolopmental-genetic constraints on the exploration of morphospace.
There is no doubt that the elongated middle finger of the aye-aye is an adaptation.
http://pin.primate.wisc.edu/factsheets/entry/aye-aye
I was going by "anonymous" in the 'Dennet on adaptation' thread but now it's "Tupaia."
to paraphrase Michael Corleone: every time I try to get out they drag me back in again...
ReplyDeleteWisdom teeth I'll grant you. Probably, prehistorically, they didn't cause major problems until after most folks had done most of their reproducing, so selection to lose them has always been weak (there is, of course, plenty of variation there--mine only came in on top, for example). I bet they have been a major source of daily misery for "old folks" for hundreds of millenia though.
Tonsils? They're packed with immunological lymphoid tissue, and that stuff doesn't come cheap. I'd bet money they were, in fact, adaptive back when people (inadvertently) ate more dirt. (oops...just-so)
Irish elk antlers? You're not kidding? Like, all the males died because they couldn't hold their heads up any more and the poor (anterless!) females had nobody to breed with? I'll grant that the term "adaptation" has to be stretched a bit for cases of extreme sexual selection (where gains in mating success trump losses in survivorship), but would you consider peacock tails similarly "maladaptive"? Because that would just be perverse.
I suggest you guys stick to your stories of neutral phenotypic traits and don't waste your time looking for "maladaptive" ones (except, of course, in cases of recent environmental change; cases like that surely exist, hence extinction).
But that's my world view. YMMV.
of course, never botherabout the fact that antler size is predicted niceky by the allometric curve of both phylogeny and ontogeny. It simply has the expected antler size for being the biggest one ever.
ReplyDeleteBut don't let this non-selective explanation bother you. Let's just assume that proportion is the result of directional sexual selection "gone wild"
Boring, huh? Not even biology.
Paleofreak, are you seriously suggesting
ReplyDeleteEh, cut off...
ReplyDeleteWhat I meant to say was; are you seriously suggesting genetic drift has no role to play in evolution?
Albeit a slight strawman question, from what I've learnt and encountered in under-grad courses, is that drift and the associated founder effect have significant effects on the alleles available for selection. Dawkins, from the little I've read doesn't cover this, and if what you've said is correct he is avoiding it.
Sanders: "of course, never botherabout the fact that antler size is predicted niceky by the allometric curve of both phylogeny and ontogeny."
ReplyDeleteDo you seriously believe that allometry is an alternative explanation to adaptation through natural selection (in this case, sexual selection)?
Yet another erroneous suggestion of mutual exclusivity.
Again, I refer you to Tinbergen. Also, try tackling Problems of Relative Growth by Julian Huxley.
In addition, even preservation of allometry may itself have to be explained, particularly where development is easily modularized and the trait constitutes a handicap, such as with Irish elk antlers. The breaking of allometric relationships occurs all the time.
The facile invocation of scaling has its own pitfalls. For example, Gould incorrectly hypothesized that robust australopithecines were much larger than gracile australopithecines due to their skull shape. In fact, these cranial differences reflect dietary adaptation, not allometry, since A. robustus (sometimes placed in the genus Paranthropus) is only slightly larger than A. africanus, not even close to allometry-based predictions.
Gould himself recognized a deviation from expected allometric relationship with kiwi eggs. He proposed that this was phylogenetic inertia from the kiwi's recent evolution from large flightless birds. Actually, the total egg mass of kiwis does confirm to allometric predictions. It is only when eggs are compared singly do they appear remarkable. In this case Gould's hypothesis of phylogenetic inertia was wrong and he would have been right if he had gone with allometry in this case (in contrast to australopithecines).
http://www.giantflightlessbirds.com/research/2007/12/are_kiwi_eggs_big.html#more
(Question for Sanders: Why are there any deviations from the regression line at all if allometry is omni-explanatory?)
The number of eggs laid by the kiwi is the real distinguishing feature; in their case, one. Clutch size was provided a powerfully predictive and adaptationist explaination by David Lack, who conducted pioneering life history investigations (Lack clutch).
Tupaia
I'm not saying the Irish elk stopped using his horns to fight for mates, you know. Of course it is an "adaptation"; you should be smart enough to realize that is not where I see the incompatibility; again, I am not denying it is an adaptation. Whta I am specifically against is the notion tahta the increase of the proportion of the antlers is due to the effect of extreme sexual selection producing ever larger antlers, as if body size were something completely independent; no sir. You will have to correct your theory to include a more realistic scenario that includes the increase in the body size of that species.
ReplyDeleteIt is, with mathematical accuracy, the predicted proportion expected for that body size, We all know the antlers get bigger and bigger along ontogeny.
But of course, of course that allometric tendencies can be "broken"!! There IS such thing as evolutionary novelty. You don't need to parade every case here. Yet, lots of allometric prediction IS possible.
Let me tell you a very simple thing: If it ain't broken, don't "fix" it.
It is case-specific thing, and the case of the antlers just as nothing wrong with it, amigo.
Sanders: "You will have to correct your theory to include a more realistic scenario"
ReplyDeletePerhaps, but I am afraid that you will have to correct your theory so you can avoid these false choices you keep asserting. An adaptation shaped by an accumulation of several genes by natural selection does not lose that status - is not defined away - simply because it can also be identified with exaptation, spandrel, heterochrony, mutation of large effect, available variation due to drift, and so on.
A non-essentialist view is that adaptiveness, neutrality, and maladaptation are not inherent properties of traits, but are conditional on the relationship between biological entities and their environments. Identifying the phylogenetic history of developmental origin of a trait, including past neutrality or current maladaptation, does not nullify the shaping role of selection in adaptation.
Prediciton is such a nice thing in biology yet some simply confront it with a wooden face. As I said, only intellectual alienation can achieve to do this with smart people. The love of a theory; the confusion of the theory with the actual phenomenon: namely, BIOLOGY.
ReplyDeleteI know perfectly well how you guys think. Give an acknowledging nod and leave it as footnote, another boring oddity with no "selection-appeal" therefore of merely almanac value. Selection is what REALLY explains the trait; what has led evolution in that direction.
From my point of view, it is likely that without this developmentla tendency, there would have been no Irish elk. And yes, that the antlers are a mere side -effect of a larger body size is a perfectly possible; in fact, in my judgement, this is the simplest an best explanation with the current data at hand.
To them Sexual selection as an explanation does not require anything about specific about previous mechanisms of development, which could be whatever. So whatever the developement is, it's nothing but an anecdote. Its never is the "crucial" bit; selection is.
So what relevance at all DID the allometric tendency have for the origin of the irish elk? none? Would there have been an irish elk with no allometry, just by sexual selection for bigger horns?
Maybe it is just another of those bizarre onto-phyletic coincidences all blown up by those nasty structuralists, huh.
"An adaptation shaped by an accumulation of several genes by natural selection does not lose that status - is not defined away"
ReplyDeleteYeah, well you have no evidence that several accumulated genes are behind the origin if the irish elk; unless you are pulling them from your deuterostomal opening.
It's just a bigger animal! Any OTHER horn size would be the unexpected thing for that size. I dont think this is at all evidence for an accumulation of genes by sexual selection. Am I the only one who sees this with clarity?
Sanders: "It's just a bigger animal! Any OTHER horn size would be the unexpected thing for that size."
ReplyDeleteSanders: "It's just a bigger animal! Any OTHER horn size would be the unexpected thing for that size."
ReplyDeleteClarity would also require distinguishing between lock-step growth allometry and adaptive allometry.
http://www.pnas.org/cgi/content/full/103/23/8733
"The classic examples of exaggerated sexually selected traits are the antlers of Irish elk (Megaloceros giganteus), which are largest in the largest individuals of this giant deer species. So it is also necessary to explain why, as species have evolved larger bodies, they have evolved simultaneously even more exaggerated ornaments and weapons.
The explanation for such positive allometries must lie with the fitness consequences of allocating resources differentially to ornaments or weapons rather than to overall body size. ...
Consider the classic case of the Irish elk: The antlers of the largest individuals are indeed very large, but they would have been even larger had the interspecific trajectories simply extended an intraspecific relationship. ...
["Any OTHER horn size would be the unexpected thing for that size."" Well, there you go.]
... the above fundamental features of allocation tradeoffs and fitness payoffs not only explain positive allometries of ornaments and weapons during the ontogenetic growth of an individual, they also explain the scaling relationships between individuals of different body sizes, both within and between populations of closely related organisms."
So it's not just an inevitable scaling consequence of growth, but an adaptive relationship of parts driven by sexual selection. Adaptation by natural selection determined the allometric scaling of secondary sexual characteristics, not fidelity to ontogenetic constraints.
In addition, I remind you that Gould's allometric analysis was limited to linear dimensions, not complex topological changes or orientation. Therefore, he did not demonstrate that these changes were simply a scaled-up version (whatever determines the scaling relationship) of a smaller ancestral deer. They may have been. But I doubt it.
"are you seriously suggesting genetic drift has no role to play in evolution?"
ReplyDeleteNo. I am saying that Dawkins thinks genetic drift has no very important role to play in the adaptive part of evolution. I personally think drift may helps populations to "travel" adaptive landscapes. Also it can remove relevant genetic diversity and slow or stop the process... Drif has several effects. Perhaps Dawkins and others think these effects cancel themselves out when considering adaptive evolution in general.
PD: saying allometry is an alternative explanation to adaptation through natural selection is like saying "using cars is an alternative to travelling"
In addition, I remind you that Gould's allometric analysis was limited to linear dimensions, not complex topological changes or orientation. Therefore, he did not demonstrate that these changes were simply a scaled-up version (whatever determines the scaling relationship) of a smaller ancestral deer. They may have been. But I doubt it.
ReplyDeleteRight! And what's also interesting is that the Irish Elk had palmate antlers. Very different from the antlers of most deer! And it would be difficult to argue that palmate antlers are necessitated by allometry. Did Gould look at antler weight?
Hi Everyone,
ReplyDeleteI'm a novice in this field, so please don't hesitate to critique my views if you find problems with it.
The source of all phenotypic change is from mutations or recombinations in the genetic code, yes? So it follows that most evolutionary changes are due to genetic drift, and only a subset which result in phenotypic changes affecting reproductive fitness will be tenable to selection.
When facing a complex organism with numerous phenotypic features, how do we know that any particular feature is the product of selection? Since the effect of small mutational changes can be amplified via developmental gene regulatory networks, some of the features may have arisen by genetic drift.
The most obvious phenotypic feature (eg. an antler) could be the least shaped by natural selection, reaching its current size and shape through neutral drift and limitations during the developmental process.
What an ugly spectacle of moving goalposts and inane adaptationist dreck. UGhh! Gives me the shivers.
ReplyDeleteWill any of you guys grow some chest hair and actually answer the question? Again: In deer in general it is true that antlers grow faster than the body, looking bigger and bigger. Do you tink that megaceros would have evolved without this pre-existing trend, by sexual selection alone in that species?
"Adaptation by natural selection determined the allometric scaling of secondary sexual characteristics, not fidelity to ontogenetic constraints"
We are not discussing the oriogin of the allometric tendency, but the origin of magceros, which happened once this tendency was in place. But you should reflect upon this: you say sexual selection "created" the allometry. Obviously yu canot concive that it could have been tge other way round: the allometry drew the species into sexual selection.
So, I guess it is up to you to show us how directional sexual selection could accumulate genes to produce not a morphology (where graulism is evident), but nothing else than an allometric growth.
Voilá,please. We are all ears. How was acquiring allometric growth the kind of gradualists accumulative many-gene thing that you would need selection for? Have you any evidence for this? Enlighten us!
Paleofreak, travelling a lot will not make you a car. first you have to have a car; then, you can travel.
ReplyDeleteSanders, this is the second time you have accused me of moving goalposts when it in fact it was you who failed to comprehend my points the first time.
ReplyDeleteIt's also noteworthy that antlers are a derivative of cranial neural crest, a tissue known to be modularized and deconstrained from tight ontogenetic linkages. With such capacity for developmental freedom, diversification in feeding (beaks, teeth) and secondary sexual traits (horn, antler) are often based on dramatic but easily achieved modifications of cranial neural crest.
See Gerhart and Kirshner.
http://www.pnas.org/cgi/content/full/95/15/8420
Tupaia
No, definitley no chest hair sprouting over here. Bye bye then folks.
ReplyDeleteWill any of you guys grow some chest hair and actually answer the question? Again: In deer in general it is true that antlers grow faster than the body, looking bigger and bigger.
ReplyDeleteAnd why do deer have antlers in the first place? Hint: it's not because of "allometry". There is nothing in the deer body as such that necessitates antlers. This simple fact would seem to be a bit of a problem for your "allometry came first" hypothesis.
I'll start answering questions when you guys answer mine, becuase the golapost moving right now is out of control.
ReplyDeletePlus I really think it boils down to answering my question.
Sanders, you have mostly presented claims and talked about chest hair. I haven't seen too many questions. Do you mean this?
ReplyDeleteHow was acquiring allometric growth the kind of gradualists accumulative many-gene thing that you would need selection for? Have you any evidence for this?
Well, first of all, positive allometry is more common in sexually selected traits like male ornaments. Why would you expect this to be the case if allometry occurs by chance?
What, did you eat martian poo?
ReplyDelete"Will any of you guys grow some chest hair and actually answer the question? Again: In deer in general it is true that antlers grow faster than the body, looking bigger and bigger. Do you think that megaceros would have evolved without this pre-existing trend, by sexual selection alone in that species?"
Answer!!! MY answer? NO!!! of course not. Yours?
Somethig that may help you is to notice the following.
If you asked me the same question: Do I think megaceros would have evolved without selection? My answer is, NO!!! Of course there is "sexual selection". But you just CANNOT do the same; you turn you head and act dumb like you've never heard the question!!hahaha.
It is your narrow DARWINIAN adaptationism that cannot acknowlege any tru relevance of development in the pathway taken by evolution, much less the origin of adaptataions.
As tupaia perhaps is beggining to realize (from his neural crest bit) , acquiring a sexually exaggerated trait may occurr in few (if not single) dramatic changes, rather than by a proces of accumulation directed by selection. If so, it is truly legitimate to say that the sexual advantages, although inmediate, could not have been involved in the origin itself of the trait. The trait would have "come first"; the sexual selection advantages, the consequence, not the cause.
If sexual selection would direct accumulation of small effects (say larger and larger horn size), it is mostly halted. The peacock tail is NOT getting bigger and bigger; species in stasis have conserved horn size for milions of years.
Is there any case of the ongoing cumulative exaggeration of a sexual selection trait? Probably not. Hahaha. Correct me if wrong!
However, from a mutationists perspective, the fact that most of the time is spent in stasis can be easily understood because events of drastic change are discrete fortunate events with a quick turnover into the most frequent thing.
But you know what? Mutations are only on way of having drastic biological change. The other way is epigentic change. I think we are all having just an ignorant conversation so long as we do not look into what epigenetic conditions can also influence these sexually exaggerated traits; body size, for instance, can change epigenetically; so can hormone production, and all this can be tied to epigenatically plastic behavior. Without taking these into account, our scenarios are lacking realism.
Sanders, please tell me that you have at least heard of James Mark Baldwin.
ReplyDeleteTupaia
of course. I've also heard of west eberhart and other "epigenetic" selectionists, like Waddington
ReplyDeleteSo, what is your point? mere iconization?
What I would really appreciate is data on how variable epigentically can antler growth be. For instance, if you dont grow that much. What about hormone balance, agressive behavior, teritoriality and the circumstances that agrrovate or losen it? What do we know about all that in deer?
I'm trying to figure out what the crux of your disagreements is. A lot of the things that you are saying are less controversial than you seem to think they are.
ReplyDeleteThe really heterodox view you have is that extremely rare mutations of large effect are the sole generator of adaptations.
Tupaia
and epiegentic change, tooo.
ReplyDeleteSelection as an importanta restriction and frequency-determinant.
But selection alone does not explain adaptation except under circunmstances that seem to escape reality
Dude, selection is SO overrated. You guys make me feel depressed.
ReplyDeleteMy problem is that people put so much emphasis on the selection part, they REALLY lose sight of everything else that is involved in the origin of adaptations (not to mention those who think as well that everything is an adaptation)
Let's put it this way: adaptationists cannot distinguish between necessary and sufficient. I know that sexual selection is a necessary part of the story; but an adaptationist will think it is a sufficent explanation for the origin of the exaggerated sexual trait, and by "runaway sexual selection" ,the exaggerated antlers of megaceros. But developmental possibilities also impart direction, making changes adaptations more or less likely.
Can we ever say selection sufficent to explain adaptation? I'm still begging for a single example of how selection shapes a microevolutionary adaptation. The fact no one has yet answered to that challenge I think is pretty indicative of how empirically fragile is the assertion "adaptation is explained by selection".
About epigenesis: Let's face it. It still needs uplifting. The three great authors mentioned by Larry were no enthusiasts; not even Gould. Even Mayr did better than Gould, even if it is indeed a miserable percentage of his work.
We can fairly say that the entire epigenetic topics remains nowadays almost completely "off-limits" to the more general public.
Now, people like Baldwin and Waddington long ago produced a very darwinian" framework for epigentic adaptation changes; darwinian, in that at the end of the tunnel they always found natural selection.
I think it is no wonder they have been mostly ignored. They simply failed to introduce epigensis into the mainstream. Why, if selection is where it's at?
Again: In deer in general it is true that antlers grow faster than the body, looking bigger and bigger. Do you think that megaceros would have evolved without this pre-existing trend, by sexual selection alone in that species?" Answer!!! MY answer? NO!!! of course not. Yours?
ReplyDeleteAnd why is there a "pre-existing trend"? If only there was some kind of prediction we could test. Oh, what's this?
THE EVOLUTION OF STATIC ALLOMETRY IN SEXUALLY SELECTED TRAITS:...positive allometry will evolve when the marginal fitness gains from an increase in relative trait size are greater for large individuals than for small ones. Thus, the optimal allometric pattern depends on the precise nature of net selection, and simple examples readily yield isometry, positive or negative allometry, or polymorphisms corresponding to sigmoidal scaling. The variety of allometric patterns predicted by our model is consistent with the diversity of patterns observed in empirical studies on the allometries of sexually selected traits.
http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1554%2F03-213
"positive allometry will evolve when the marginal fitness gains from an increase in relative trait size are greater for large individuals than for small ones"
ReplyDeleteHuh, I see. And under what conditions exactly are fitness gains from an increase in relative trait size greater for large individuals than for small ones, you know to make this wonderful "prediction"?
Let me guess: When a sexually selected trait grows with positive allometry!!
Prediction? More like woodenhorse-rocking.
Any one can see that we can turn this around and say "positive allometry of a sexually selected trait leads to greater sexual succes of large individuals. If we have a negative allometry, the seuxal suces of bigger individuals will not be so great. Voilá, it's consisten with the pattern so fthe real world! relaity!! I've just PREDICTED the very same thing stating it is all a consequence of the type of allometry you have.
Let me state it:
"if a sexually selected trait develops as a positive allometry, there will be greater sexual succes of the bigger individuals"
Gee, I'm feeling like a freakin nostradamus!
You are some bonehead. Are you sure you aren't in the process of evolving antlers yourself?
ReplyDeleteThat article doesn't say what you think it says. Why not read it? I guess it's easier to misrepresent what others say.
Any one can see that we can turn this around and say "positive allometry of a sexually selected trait leads to greater sexual succes of large individuals.
All right, how would that work? You ask us to believe that in nearly every species in which a positively allometric trait has appeared by chance, the entire mating system, behaviour and development of the species then inexorably evolves to accommodate this single trait (rather than co-evolves). I'm sorry, that's way too ultraselectionist for me.
Another way to put it: If the presence of positively allometric traits is independent of selection, why are there relatively few exaggerated female ornaments?
ReplyDeleteNo., Windy. No more questions until you finally answer mine. You've had lots of time to grow some balls by now, haven't you.
ReplyDeleteyou still don't answer and ask, quite stupidly I reckon "And why is there a "pre-existing trend"?
The positive allometry of antlers pre-existed the evolution of the large megaceros. Period.
Is there any other thing you want to play dumb about, AGAIN?
I have ony so much patience with adaptionist alienation.
I'm not really here to read all the articles you wish to pin up, windy. There is only some amount of head shaking I can do without neck pain, and ena enorimosu literature written with an adaptationist cap.
ReplyDeleteIf you are not adept enough at presenting ideas in discussible form at a blog conversation, that you can't save me the read, then there is little point to it, isn't it.
I am juts left to wonder, under what conditions other than a pre-exsiting allometry, does it occur that fitness gains from an increase in relative trait size greater for large individuals than for small ones, such taht we can predict that positive allometry WILL evolve (custom-made special order?)
Thi is a questio you should have been able to answer right away.
Unless I'm compeletely right: There is not ture prediction of allometry by selection there. Just consistency with exisiting patterns, as the abstract says.
Sanders: "The positive allometry of antlers pre-existed the evolution of the large megaceros."
ReplyDeleteThis is a phenomenon of sexual selection operating in a lineage, the most extreme expression of which appears in Megaloceros. The fact remains that this scaling relationship was in fact determined by sexual selection, and not "just a bigger animal." As the intra-species studies show, a merely bigger animal (as an ontogenetic default) wouldn't have such big antlers.
I'm still trying to pinpoint your views. You really don't sound too much like Stuart Kauffman, who was convinced by John Maynard Smith of the potency of selection. And you are not of the Baldwinian school, which you correctly pointed out is selectionist (and hence not really that different from neo-Darwinism). Richard Goldschmidt comes to mind. He also discussed environmental induction of phenocopies of macromutations, which I suspect is more like your view of epigenetic change than the Baldwinian-Darwinian view.
If I understand you, you believe that selection is an eliminative force but not a creative or generative force (accumulation of small changes resulting in complex adaptations, as discussed in The Blind Watchmakers).
But even neural crest did not suddenly appear with its all of its protean properties, allowing for traits like huge Irish elk antlers, through saltation. There were precursors, such as the protoneural crest of tunicates. (Yes, the role of this tissue changed; it was co-opted for new functions. That's a perfectly selectionist phenomenon.)
A series of steps, guided through morphospace by natural selection (with some epigenetic biases), adapting to current selective pressures (and are often preadaptations of future adaptations), as features of complexity and optimal design (or close enough) are formed.
Sanders, thank you for your uncharacteristically cogent and calm comment above (Thursday, September 06, 2007 11:43:00 PM). I think I can now see a way out of this stupid argument about deer antlers. This is going to take a while, but please bear with me, as I want to be absolutely clear once and for all.
ReplyDelete(But first, Sanders, with regard to your tediously repeated challenge, why aren't the hundreds of known field examples--data! measurements!--of natural selection on polygenic traits (the Grants's work on Galapagos finches is the best known) good enough for you? Knowing what we know, would you regard "the beak size of a Medium Ground Finch" as an adaptation? Or do you want to reserve that term for brand-new body parts (like, I guess, the origin of beaks themselves?). For whatever reason that empirical microevolution is not persuasive to you as a source of adaptation, your asking for field examples of "shaping by natural selection," including serial replacement of alleles, sets the bar mighty high considering that people have only had about 40 years in which it was even possible to look for it! Plus, strong and rapid (and therefore easily detectable) evolution by directional selection is only predicted (by us "adaptationists") to occur during and following a change in environment anyway; give us some time! Maybe the closest thing so far is Richard Lenski's work on bacteria (in the lab, of course).)
OK, deer antlers: here are the data (I love you, Google, BFF). The symbol M is the extinct Irish elk.
Empirical: positive interspecific allometry for antler size in cervids, Megalocerus right on the (reduced major axis) prediction line. Sanders is correct say that its antlers are "typical" for deer, given its body size. (Two complications: first, the allometry is specifically for antler length, whereas in my opinion mass would be a better general measure of "antler size," and this is basically what somebody pointed out above wrt palmate antlers; second, because M is the largest species in the dataset, it has a very strong influence on the regression and therefore plays a not-trivial role in actually setting the prediction line to which it is being compared. But onward with the argument.)
Positive allometry is extremely unusual. Almost anything else biological scales either isotonically (directly proportional to body size, scaling exponent = 1) or negatively (e.g. surface area at 0.67, metabolic rate at 0.75). So in one way it's the evolution of the positive allometry among cervids itself (1.85) that needs to be explained, not the extreme length of the antlers of Megalocerus specifically. And this has to be explained both proximately and ultimately (pace Tinbergen). Only males have antlers, so the only reasonable ultimate explanation is sexual selection: the larger the antlers the more successful matings (for whatever reason). The bigger the better, size matters, etc. In each species (with its body size), we can hypothesize pretty confidently that antler size is limited by opposing natural (or, much less likely, sexual) selection . So why is the resulting allometry of antlers positive? It cannot be some deep-seated locked-in developmental constraint, because there is considerable variation around the empirical regression line (check out the largest living cervids, moose--A on the figure). So we have to look elsewhere for our proximate explanation, and there are probably several testable possibilities...my first guess would be some sort of mechanical constraint setting positive allometry of the strength of neck muscles or nuchal ligaments.
In other words, the positive allometry of deer antlers seems best explained as a combination of consistently positive sexual selection opposed by natural counterselection plus (perhaps) a purely mechanical engineering constraint. Sanders, I think all this is consistent with your position, so far anyway.
So, in view of the above, are the huge antlers of Megalocerus adaptations? I still say YES, very probably, and for two reasons:
1) There is clearly possible plasticity in antler size, and the actual antlers of each species must result from the strength of counterselection in its particular biotic environment (food, predators, parasites). Because, as proven by moose, it is possible to have smaller antlers than predicted, it follows that the fact that the antler size of Megalocerus is on the regression line rather than below it must be due to continuing positive sexual selection--an adaptation, in my book. (This is G.C. Williams's point when he writes that the empirical study of natural selection is chiefly about explaining the maintenance of a putative adaptation, not its "origin." Paradoxically, it's mostly about explaining the absence of phenotypic evolution.)
Second--and here, I think, is the real reason that it makes no sense at all to regard "mutations of large effect" or "epigenetics" as an alternative explanation to selection--let's do a thought experiment. We have a population. A mutation of large effect appears. This occurs in the germ line of one individual, or in a large enough population, conceivably a few simultaneously. Now what? With regard to Darwinian fitness (in, of course, the current environment), the phenotype resulting from the mutation may be deleterious, neutral, or beneficial. How does it spread through the population to fixation? Either it doesn't (deleterious), by drift (neutral), or by selection (beneficial). Theoretically, those are the ONLY possibilities. If a phenotype spreads through a population to fixation, it must, therefore, either be neutral or an adaptation. It doesn't matter whether it appeared all at once (from a mutation of large effect) or was gradually "shaped by selection," its "origin" at the population level must involve either drift or selection. And the maintenance of a trait in the population/species must also involve either selection (therefore an adaptation), neutrality, a total lack of genetic variation, or a recent environmental change.
Large antlers are obviously not "neutral" in terms of survival, energy allocation, etc. Therefore, that deer have antlers at all, both their origin and their maintenance must be due to selection.
I just don't see any other alternatives. What do you pluralists think?
positive allometry in antlers causes fitness gains for larger individuals?
ReplyDeletereductio ad absurdum:
melanism in moths causes industry.
No., Windy. No more questions until you finally answer mine. You've had lots of time to grow some balls by now, haven't you.
I do just fine without balls, thank you, just as most female deer do fine without antlers. I really don't know how to get this point through to you. Luckily Sven had more patience.
are you really dumb enough to think it that way, windy?
ReplyDeleteIt's like this:
under sexual selection for a trait, positive allometry of this trait will give larger sizes greater fitness (than, say, negative allometry)
Under industrialization selective pressures, melanized moths present greater fitness
Is selection a part of understanding this phenomenoen? yes, of course!. A NECESSARY part. there is no understanding without it.
Is selection be sufficient to make this adpataions come about? No. Development must also come up with the trait: a black moth ( a one-allele mutation and evident case of "adaptation first") or a posotove allometry in a sexually selected trait.
It is AS NECESSARY as selection.
But since you are creepily adpataionist, there is not enough generosity i your brain to acknowledge this fact; hence, you REFUSE to answer my megaceros question.
C´mon. YOU know you WANT to say YES; previous developemtn was irrelevant for the evolution; sexual selection is SUFFICIENT for you. OK?
You have no balls or ovaries or nothing.
This question?
ReplyDeleteDo you think that megaceros would have evolved without this pre-existing trend, by sexual selection alone in that species?
Your question has a faulty premise and therefore it is not enough to say "no". The pre-existing trend of positive antler allometry in cervids is in itself due to sexual selection. Therefore "sexual selection" is a better although not sufficient answer for the size of megaloceros antlers than "pre-existing trend".
The positive allometry of antlers pre-existed the evolution of the large megaceros. Period.
Sexual selection for antler size preceded the evolution of the large megaloceros. This is not guesswork, it's apparent from the phylogeny just like positive allometry.
Could you please at least look at Sven's excellent answer and note the comments about moose.
Sanders seems to feel that the large body size of Irish elk resulted from sexual selection for ever-larger antlers. I suppose that's possible, though if true it's hard to see why all deer don't get bigger and bigger. Something special about the Irish environment that uniquely permits hugeness??
ReplyDeleteI was thinking of body size as a separate trait, with various selection pressures affecting it, and then sexual selection favoring the largest possible antlers, which are relatively larger for larger body sizes. I wonder how sexually dimorphic in body size they were.
Sanders seems to feel that the large body size of Irish elk resulted from sexual selection for ever-larger antlers.
ReplyDeleteThat would be relatively sensible and uncontroversial, I think. But isn't he claiming that fixed allometric trends precede and cause sexual selection?
Why doesn't Larry put someone on the list of icons that is closer to his own view, such as Nei?
ReplyDeleteDawkins is the anti-Nei. In his review of Behe's latest book, Dawkins refers to “generations of mathematical geneticists, who have repeatedly shown that evolutionary rates are not limited by mutation”, arguing that if Behe is right, “the entire corpus of mathematical genetics, from 1930 to today, is flat wrong”.
Nei isn't one of those mathematical geneticists who have proved that evolution does not depend on the rate of mutation. But for Dawkins, the only true theory of evolution is the "synthetic" or "neo-Darwinian" theory in which evolution does not depend in any critical way on the rate of mutation because there is always abundant variation in the "gene pool".
One of the few important things that we have learned, or should have learned, in the past 40 years, is that the rate of evolution DOES depends on the rate of mutation. Whatever its superficial plausibility or verbal appeal, the "gene pool" notion is nonsense. Of course nearly all populations have variation, but the idea that this represents a "gene pool" that serves as a kind of magic hat-- out of which selection can pull any trick-- is nutty and now has been completely overthrown (except in the mind of Dawkins and other neo-Darwinian die-hards).
What happens in evolution depends, not only on the fact that variation happens, but on the rate at which different kinds of variants emerge. This is a proven part of the causation of evolution. Yet some people continue to assume that invoking selection is sufficient to account for evolution.