Discover magazine sponsored a contest where you had to produce a two minute video explaining evolution. The judge was PZ Myers. Here's how PZ explains his choice [see The Winner: Evolution in Two Minutes].
Oh dear. Repeat after me, PZ, evolution is not natural selection!
This is, indeed, the 21st century, and not the Victorian England of Charles Darwin. We now know that evolution is any change in the frequency of alleles in a population. We know that for evolution to occur the change has to be genetic. We know that populations evolve, not individuals. We know that there are two main mechanisms of evolution: natural selection, and random genetic drift. It's a good idea to mention that variation within a species (population) arises from spontaneous mutations that create gene variants called alleles. That's what needs to be explained in two minutes.
Here's the winning video from Scott Hatfield, a high school biology teacher, and, more importantly, a blogger at Monkey Trials. Scott's a cool guy but it's not the video I would have chosen.
25 comments :
you can't expect too much from people that are non-specialiasts (including Larry), even less so given the intellectual diversity of opinions among real specialists. On many topics there is no standard or consensus, but a standing diversity of viewpoints.
Even though a majoritarian group has existed (darwinian /adaptationists) these have never enjoyed full hegemony, in fact it's hegemony has been frankly in decline, with a solid evo-devo community that goes quite beyond the study of selection and drift.
Larrry you are the uncle tom of drift. So long as you adscribe adatation to natural selection only, you're firmly in the adaptationist/selectionist camp.
A. Vargas said...
Larrry you are the uncle tom of drift. So long as you adscribe adatation to natural selection only, you're firmly in the adaptationist/selectionist camp.
What other forces are at work on allele frequencies in a population besides Natural Selection and Drift? Or should I say other primary forces that evo-devo are talking about in particular? I am curious since I am mostly on the molecular end of evolutionary theory and we predominantly talk about selection and drift on sequence data.
Even with something like Constructive Neutral evolution selection tends to come in late in the game although it is an adaptation that arises primarily through neutral mutations fixed by genetic drift.
At sequence level, you should also consider mutation, souldn't you.
At a aphenotypic level, non-genetic changes in the phenotype are as important as selection in guiding the course of evolution, specially given their relation to adpatation (something larry cannot understand)
In any case what I said was:
"So long as you adscribe adatation to natural selection only, you're firmly in the adaptationist/selectionist camp"
My point is that drift has been shown to have a CRUCIAL role in the origin of adpatations, and that includes studies at the sequence level (see fish opsin evolution). Larry still doesn't adjust this bit of information into his brain and continues to parrot that only natural selection produces adaptation.
Larry declares himslef a Gould fan buthe has not assimilated Gould's message on the role of non-adpative spandrels in the origin of adpatations.
Mutation is a given, I wasn't aware anyone was ignoring mutation or even variability in mutations rate and related topics.
I also don't think Larry has ignored the idea of non-adaptations playing a role in later adaptations, which is what I was getting at with Constructive Neutral Evolution. Although I am aware that for many it is an idea that has not caught on. It is of course absolutely crucial and gets people out of the thinking of "waiting around for an adaptation to rescue a "sick" phenotype."
While you are right I don't think Larry is as guilty of this as you make him out to be.
If I were you I'd keep an eye wide open for mutation rather than ignore it as "given". Changing mutation rates can be easily confused with drift-selection.
Larry (quite stupidly) insist that only selection produces adpataion...enough said, then.
with a solid evo-devo community
I can only get so excited about a field that describes only a small subset of life by focusing only on metazoans.
In terms of doing science I always "keep my eyes open for mutation", mutational rates are something always factored into the work I and others do in Molecular phylogenetics. By "assumed" I meant that mutation is always assumed as a factor in discussions about evolution, and in fact is something Larry specifically mentioned in this blog post.
As for the rest, I don't think Larry dismisses it at all. Thats certainly not the impression I have gotten from this and many other blog posts on the subject. But even in the case of non-adaptive spandrels that later lead to adaptations (or in the case I brought up of Constructive Neutral Evolution), Selection enters the picture at some point, along with the question of drift, and as always mutation providing the raw material, etc. I don't think Larry has neglected this at all.
Now whether you think he has given it enough emphasis is another question.
The Other Jim Said...
I can only get so excited about a field that describes only a small subset of life by focusing only on metazoans.
Hear, hear. Something I whole heartedly agree with. The majority of life on Earth and its evolution is too often overlooked in favour of Metazoa and Plants and their peculiarities.
Drift and selection are insufficient notions for understanding the evolution of any group, metazoan or not. We need to study the relationship of genotype tp phenotype, as well as mechanisms of inheritance beyond the dna sequence. These are black-boxed or igrnored by those approaches that by mere definition exclude anything but populational frequencies of genes.
"Now whether you think he has given it enough emphasis is another question"
No. He thinks drift only has a role in the origin of non-adaptive traits. This is a bad misconception. Give drift its due.
No. He thinks drift only has a role in the origin of non-adaptive traits. This is a bad misconception. Give drift its due.
I'd like to know exactly where he espouses this. Maybe he will come here and answer himself but I'm reasonably sure this is not a good summary of his thoughts.
Natural selection is not evolution
--Opening sentence of The Genetical Theory of Natural Selection by R. A. Fisher
Let's be honest for once and admit the truth:
We don't have a clue what the mechanism of evolution is.
Natural selection and genetic drift affect the frequency of alleles in populations, but there is not a shred of empirical evidence, either observational or experimental that supports a nexus, real or hypothetical between these trivial effects and the highly organized structures, processes and systems found in living organisms.
And that's that !
charlie wagner said...
Let's be honest for once and admit the truth:
We don't have a clue what the mechanism of evolution is.
Thats ignorance, not honesty.
"I can only get so excited about a field that describes only a small subset of life by focusing only on metazoans."
+1000
I think protist cellular evo-devo would be so cool (ie. has great potential to reveal a neat trick or two about cellular development, as well as evolutionary mechanisms on that scale; and who know what else...) Even better if prokaryotes are included as well!
(the protist side is what I dream of working on eventually, somehow, if someone's crazy enough to admit me to grad school, that is >_>)
And who's this 'charlie wagner' persona? Appears to have quite a backstory on this blog...
Larry: “evolution is any change in the frequency of alleles in a population”
Aw, Larry, stop being a crusty pedant! :)
Yes, that is *ONE* meaning of the word “evolution”, but there are others, and they are not necessarily wrong. Evolution can also mean “change in morphology over time”. This is what, for example, Neil Shubin means (and is how it is quantified) when he talks about the evolution of land animals from fish. It is what paleontologists refer to (and how they quantified it) when they talk about periods of “stasis”. And that was the only meaning of the term in a biological context long before we knew anything about genetics.
And, I will note, it would probably be selected by the vast overwhelming majority of humanity if you were to ask them what the term “evolution” means to them. Those surveys and polls of peoples views on evolution and those questions of presidential candidates? You are getting their opinion about “change in morphology over time”, not their opinion on “change allele frequency in populations”.
Divalent says,
Evolution can also mean “change in morphology over time”.
So, you support the idea that the increase in height among Europeans over the past few hundred years is an example of evolution?
That's not what I think of when I think of evolution. My definition of evolution requires that changes have a genetic component.
If we don't know that changes were genetic then we can infer it by looking at morphology as a surrogate for alleles. But it's only a surrogate and we need to keep that in mind.
We're talking about SCIENTIFIC definitions here and not the incorrect views of the general public. If you're making a video to explain evolution then presumably you want the science to be correct. Right?
The alternative is to pander to the misconceptions of the general public instead of seizing the opportunity to correct them.
Come to think of it, allele frequencies aren't the only things that change in evolution... one mustn't forget cytoplasmic and cortical inheritance. It seems like at least some of the striking cellular complexity among the ciliates in inherited via non-genetic means, and selection (of both types) would act on that as well, along with 'mutations' in transmission. So we've got selection, heritability (which is missing in environmentally-induced changes), and mutation, the three prerequisites for an evolutionary system.
I guess one could argue that a particular arrangement of kinetids could be considered as an 'allele', albeit a rather non-discrete type of one. But I don't know how many would agree with that, especially since there may or may not be a particular strict replicator unit in that case.
And we shouldn't just dismiss non-genetic inheritance because you can't run it through a sequencer - cellular evolution may explain a lot where genetic evolution fails to reveal clues (esp. when discussing evol of the euk cell) (I think I've been reading too much TC-S lately...)
Can't we just say that evolution is heritable, mutable, selectable change?
Psi Wavefunction says,
So we've got selection, heritability (which is missing in environmentally-induced changes), and mutation, the three prerequisites for an evolutionary system.
Oh dear. You haven't been paying attention.
Selection is not a prerequisite for evolution. You see, there's this thing called random genetic drift ....
Mutation isn't required either, at least in the short term. You can have changes in allele frequencies over time without introducing new mutations. Changes in the blood type alleles in human populations are good examples.
Larry: That's not what *I* think of when *I* think of evolution.
That's *exactly* my point. And as much as you might not like it, the world is not necessarily going to (or have to) conform to your desires. The word has different meanings in different contexts, several of which *predate* your narrow technical definition.
The word, term, and concept of "evolution" is not *just* some obscure technical label used by biochemists. In other related fields, there are many that use it with to express concepts that don’t strictly conform to your definition. And in the general public, the term has been used to denote the concept of “morphological change over time” long before it was even possible to formulate your definition. Just because Larry Moran finds his definition useful for *his* purposes doesn't mean that everyone else has to now go find some other term to express different, but well established, meanings. Essentially, you want to restrict the term to denote the underlying process that we now know explains the phenomenon that the term originally denoted.
We're talking about SCIENTIFIC definitions here and not the incorrect views of the general public. If you're making a video to explain evolution then presumably you want the science to be correct. Right? The alternative is to pander to the misconceptions of the general public instead of seizing the opportunity to correct them.
Even if you were right, that the scientific establishment agrees on a “correct” definition for scientific purposes (you are not!), it’s a bit arrogant to characterize the general publics use as a “misconception”. (Should the physicists get bent out of shape whenever someone uses the terms “strange” or “charm” in their non-quantum mechanical senses?) Whether you like it or not, the term evolution has a definition in the common parlance, and that definition captures *THE* essential aspect of what makes evolutionary theory a politically charged issue. IMO, your objections just reinforce the stereotype of the pedantic, pointy-headed, ivory-tower intellectual. (You can take that as a compliment! :)
By selection, I meant negative selection. But surely there must be some form of at least weak selection, even if just a consequence of physical limitations? As soon as resources in a system become finite in any way (and physical laws exist), selection automatically occurs. And I've yet to come across an evolutionary system with boundless, infinite resources (even cultural evolution has strict limitations - total human population and human brain structure for a start).
To summarise - selection is an inherent property of any system where evolution can occur, at least past the very initial state. This process, however, is not necessary for the various 'subprocesses' in the system, although it tends to creep in anyway (again, negative selection, that is)
---
In order to -have- alleles, mutation surely must be a prerequisite. I'm talking about -initial- conditions for evolution, not an intermediate snippet of the process. Of course selection and mutation aren't required for all evolutionary processes, I've moved beyond that (unlike some others). I had in mind the overall evolutionary system as a whole. If we're discussing the definition of 'evolution', surely we must be considering the entire system?
(and also, drift wouldn't happen without [negative] selection, would it? otherwise the population will grow infinitely, and...allele frequencies wouldn't really change much.)
Lastly, another problem I have with 'change in allele frequencies' is that some other modes of evolution (eg. cultural) may or may not have an equivalent for that. Since the presence of replicators in that context is still hotly debated (and probably will be until we begin to have an idea of how the brain works), and as far as I know, that would be a prereq to having allele-like things, it may be worth considering slightly more general definitions of evolution for the time being.
But just to clear thing sup - claiming that [negative] selection is necessary for (or rather, inherent in) the evolutionary system as a -whole- does not make one an adaptationist. But it's kind of difficult to ignore the background of negative selection when dealing with biological evolution, no? Even Constructive Neutral Evol requires some degree of negative selection (otherwise, how would a gene/structure get fixed?)
Cheers,
-Psi-
So Divalent, I just ripped this from an online dictionary...
grav·i·ty (grv-t)
n.
1. Physics
a. The natural force of attraction exerted by a celestial body, such as Earth, upon objects at or near its surface, tending to draw them toward the center of the body.
b. The natural force of attraction between any two massive bodies, which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
c. Gravitation.
2. Grave consequence; seriousness or importance: They are still quite unaware of the gravity of their problems.
3. Solemnity or dignity of manner.
If I choose to stick to definition 3 only, do physicists have to accommodate me?
Divalent says,
That's *exactly* my point. And as much as you might not like it, the world is not necessarily going to (or have to) conform to your desires. The word has different meanings in different contexts, several of which *predate* your narrow technical definition.
Gimme a break. My response was sarcastic.
What we're looking for is a definition of evolution that's useful. We want one that will be agreed to by a majority of knowledgeable scientists. One good place to look for a consensus definition is in evolution textbooks.
Yes, that is *ONE* meaning of the word “evolution”, but there are others, and they are not necessarily wrong. Evolution can also mean “change in morphology over time”.
Okay. Let's examine your definition and see if it's sustainable.
How about answering my question? Is the morphological change of increased height among Europeans an example of evolution?
If you answer "yes" then we can terminate this discussion since your definition is useless. If you answer "no" then why do you advocate a definition that you won't support?
And that was the only meaning of the term in a biological context long before we knew anything about genetics.
That's a ridiculous argument. We're not arguing about how evolution was defined before we knew about population genetics. We're arguing about how we define evolution today in light of everything we've learned since Mendel.
And, I will note, it would probably be selected by the vast overwhelming majority of humanity if you were to ask them what the term “evolution” means to them.
I can't believe you just said that. Since when do we let the general public tell us how to define scientific terms?
Polls in the USA tell us that a majority may not even accept evolution by any definition. They aren't exactly a reliable source of knowledge.
You may be proud of the fact that your preferred definition of evolution corresponds to that of a scientifically illiterate general public, but many of us would be worried about such a correlation.
First of all, Larry, thanks for mentioning me on your blog. I think you're a pretty cool guy, too, to the point where (you may recall) that I wrote and asked permission to use one of your longer essays as a primary source. I hope (memory fails me) that I was gracious enough to thank you then.
Secondly, when I made the video, I took as my cue the original statement, which clearly was encouraging participants to draw attention to what Charles Darwin importantly got right in the year of his bicentennial. I certainly don't discount other mechanisms for either generating or culling variation other than natural selection. I do believe, however, that the predictive and explanatory power of natural selection has grown in recent years, and that the insights from evo-devo are largely complementary to, rather than opposed to the modern synthesis. I suppose we may difer on this point.
Finally, I am amazed at the misplaced confidence of some of your commenters here.
For example, the notorious CW expressing the view that we are completely ignorant of the mechanisms underlying evolution. Surely he understands that evolution is defined genetically, and that there are all manner of well-described mechanisms affecting allele frequency? There is a vast literature on the subject!
Since CW can not be completely ignorant of that literature, then he must be attempting to reframe evolution in terms of higher-level questions such as the origin and rearrangement of body plans. If so, then he's really not playing fair. You can't expect us to have a really complete account of how development has been altered over evolutionary time until we have a reasonably complete account of how genes direct development during a single organism's lifetime. Which we don't. Yet.
Anyway, I've rambled long enough. Thanks for the mention, love your blog, take care!
Scott
"Is the morphological change of increased height among Europeans an example of evolution?"
Why not? Phenotypic plasticity is often part of the evolutionary process, and even of protocols of artificial selection. Yes, environmentally induced phenotypic plasticity. Overfeeding is the first step in order to artificially select for bigger size in chickens. Without the environmental stimulus, the growth potential may not be expressed. thus, environmentally induced phenotypic plasticity uncovers hidden genetic variation.
The sources of biological change that we observe in evolution include phenotypic plasticity. This fact is as patent as noting that changes in populational gene frequencies are also a part of evolution.
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