Rama Singh is a Professor in the Department of Biology at McMaster University in Hamilton, Ontario (Canada). He happens to be the supervisor of Carlo Artieri, who writes Musings of the Mad Biologist.
Carlo noted on his blog (Evolution is a fact, not just theory...) that his boss has just published an article on evolution in the local newspaper. Read it at: Evolution is a fact, not just theory.
I'll quote the subheading and a couple of paragraphs and leave it up to my readers to discuss. Is this a good example of how scientists should explain evolutionary biology to the general public?
The only unproven area is Darwin's natural selectionI'll get the conversation going by pointing out that well before the 150 years Professor Singh mentions in his article, random genetic drift was proposed as a pretty good theory about how evolution can occur. It may not be "better" than natural selection but I think it's good enough to have deserved a mention.
...
Living organisms, on the other hand, evolve by variational evolution that depends on the survival and reproduction of the "fittest" individuals in the population, which is composed of many genotypes.
Unlike evolution, which is taken as a fact, the theory of natural selection, Darwin's mechanism for evolution, has come under criticism as to whether it is sufficient to explain evolution. In particular, early developmental biologists questioned if natural selection was adequate to explain the diversity and complexity of life.
Yet after 150 years of vigorous research (and many Nobel prizes!), no one has come up with a better theory. In fact, the more scientists have explored biology, the more they have become convinced of the facts of evolution.
Natural selection is a fact of everyday life. Resources are limited, individuals differ in their survival and reproduction, and evolution is a common sense conclusion deduced from facts and reasons. The problem with evolutionary change is that it takes place on such a slow place that we do not see it. However, we can imagine how evolution occurs by looking at the spectacular variety of food plants, flowers and domestic animals that we have produced by using the same principles of genetics and selection that nature uses. We may not witness the origin of species, but we have witnessed species becoming extinct in our own life time.
Doesn't the existence of evolutionary stasis (including "living fossils") prove that drift - especially drift in genes related to phenotypically variation - is generally not all that important? If drift (as well as selectively neutral phenotypic variation, which you link to drift) was as important as you say, wouldn't all species morphologically "drift" all over the place rather than displaying statis for millions and tens of millions of years? I know, you'll protest that drift only is a factor in small populations. Then explain the living fossil, the coelacanth. The fact is that the common phenomenon of stasis is a sure sign of stabilizing selection. Admittedly, drift sometimes matters - usually in boring, nonconsequential, phenotypically invisible genetic variation.
ReplyDeleteThere are aspects of the article that we felt would be received poorly - He's already caught flak for using the analogy of automobiles (OMG they're designed!!!!).
ReplyDeleteAs a post-doc of R.C. Lewontin, my supervisor as much as anyone, is not an adaptationist. Our lab does a lot of speciation work, and we're already bristling at the recent Scientific American 'allegation' that neutral evolution has been somehow ruled out of speciation.
I know that Dr. Singh has written several articles in the Hamilton Spectator over the years, and I've been surprised at how detailed some of them are (he had a rather in depth article about human genetic variation in 2002). I'm not sure that this would have been the best forum for bringing in random genetic drift, though I'm sure that there could've been a way to do it. I'm just more impressed that he takes the time out of his work to write this kind of stuff because not every scientist does.
Carlo says,
ReplyDeleteI'm not sure that this would have been the best forum for bringing in random genetic drift, though I'm sure that there could've been a way to do it.
Of course there was a way to do it.
Here's what Rama said,
Unlike evolution, which is taken as a fact, the theory of natural selection, Darwin's mechanism for evolution, has come under criticism as to whether it is sufficient to explain evolution. In particular, early developmental biologists questioned if natural selection was adequate to explain the diversity and complexity of life.
Yet after 150 years of vigorous research (and many Nobel prizes!), no one has come up with a better theory.
I would have replaced the last sentence with.
Today, 150 years after the publication of "On the Origin of Species," we know that natural selection is not the only mechanism of evolution. Much of the diversity we see around us can easily be explained by accidental evolution—the mechanism is called random genetic drift and it is the opposite of adaptive natural selection.
Natural selection is still the only known mechanism when it comes to explaining adaptations. Darwin was 100% correct about that.
Furthermore, the fact of evolution—that life has evolved over billions of years from a single common ancestor (or a small number of common ancestors)—has been so overwhelmingly verified by additional evidence that it is now considered a fact and not a theory.
How hard is that? My version has the disadvantage of being slightly more complicated but it has the advantage of being a lot more correct.
When it comes to writing for the general public, the debate is over "dumbing down" versus "accurate." I always come down on the side of "accurate." How about you?
Genetic drift does occur in some conditions, as does natural selection. It's not really an either/or question. They both have differing effect in different environments.
ReplyDeleteWhen it comes to writing for the general public, the debate is over "dumbing down" versus "accurate." I always come down on the side of "accurate." How about you?
ReplyDeleteYou'll find no disagreement from me. I've read enough Gould to think that there's a proper way to convey complex concepts. Even if the public fails to understand it, scientists retain the ethical 'high-ground'.
However, now I'm caught in the awkward position of agreeing with you that my supervisor could have done a better job ;-)
"Yet after 150 years of vigorous research (and many Nobel prizes!), no one has come up with a better theory"
ReplyDeleteI don't see anything wrong with this general statement. He probably should have stated random drift as another mechanism, but it's not a "better" one. I think for the layman this is not too bad. The way I see it, a layman can understand evolution quite well without knowing about random drift. As for the debate between "dumbing down" and being accurate, I too don't think it should be an either/or question. On the other hand, it is quite difficult to achieve flawless accuracy and yet retain clarity, simplicity and accessibility; very few people can do this. Maybe you can write an evolution book for laymen and demonstrate how it can be done.
Larry: Much of the diversity we see around us can easily be explained by accidental evolution—the mechanism is called random genetic drift and it is the opposite of adaptive natural selection.
ReplyDeleteThere are a lot of terms in this passage that are ill defined. In particular I really don’t understand what you mean by saying drift is the opposite of NS. Since you say “diversity we see around us” I take that to mean you are referring to phenotypically visible differences.
It is one thing to say that a particular mechanism can account for some difference, it is another to prove it. NS can "explain" every phenotypically visible difference between two species at least as easily as (and often better than) random drift can, but until one has gone beyond the principle of the process and prove that *that* mechanism was the one responsible, it remains a conjecture (drift *or* NS). And with respect to phenotypically visible differences, NS often has the more plausible argument.
Since both NS and drift occur via the same basic process, it can be very hard to distinguish them. (Drift is the change in allele frequency in successive generations due to random chance only, whereas NS is the *same thing* except one allele has a probabilistic advantage.) Even where one tracks allele frequency over hundreds of generations (in a constant environment!), unless a particular allele gives an enormous advantage, evidence for NS from just that data would not be clear. But that would be no evidence that it was purely drift.
Carlo says,
ReplyDeleteHowever, now I'm caught in the awkward position of agreeing with you that my supervisor could have done a better job ;-)
I promise not to tell him ... for a price. :-)
Do you know that Rama and I had a joint NSERC grant back in 1982-84?
divalent says,
ReplyDeleteAnd with respect to phenotypically visible differences, NS often has the more plausible argument.
Really? Next time you're out on the street look at the people around you. You will see tons of phenotypic differences that have an underlying genetic component. This is what diversity is all about.
What percentage do you think is in the process of being fixed by natural selection?
I promise not to tell him ... for a price. :-)
ReplyDeleteAnd thus I am reminded to be careful of what I blog about when I'm signing my name to it...
Do you know that Rama and I had a joint NSERC grant back in 1982-84?
Actually, I did! A few months ago I mentioned to him that I'd read an interesting post on your blog; to which Rama replied that he knew you and that you'd previously collaborated in looking into the evolutionary dynamics of heat-shock proteins (I didn't get any details). Not sure if he actually ever reads the blogosphere though, I should send him a few links.
Larry said: "Next time you're out on the street look at the people around you. You will see tons of phenotypic differences that have an underlying genetic component. This is what diversity is all about. What percentage do you think is in the process of being fixed by natural selection?"
ReplyDeleteThe US is an ethnically diverse country with people just a few generations removed from ethnically uniform populations from all corners of the world. I can think of plausible explanations for differences in outward appearance (shape/color of eyes, hair type/color, shape of nose and cheeks, butt size, etc) in the source populations, mostly related to sexual selection of appearance (to a standard that is local and can "drift" in the sense that it is arbitrary and dependent on what the mean of the population is, but selected nonetheless).
I can prove none of that for any particular feature, but there is lots of evidence to suggest that animals (including humans) have such mating preferences (e.g., subspecies/varieties prefer to mate within their group when given a choice). So anything that affect outward appears I would presume is likely to be (or at least was before modern times) something that was the focus of sexual selection.
OTOH, your job is tougher. To credibly claim it is drift you have to rule out selection at any time from the moment the different allele appeared until it became fixed in the source population.
Have you, or anyone, done this for any allele that underlies any of this "diversity" you speak of?
If not, what is the basis for your presumption that "much" of it is due to drift? You are the one making the claim. Back it up with reasons and/or evidence.
http://vadlo.com has some nice cartoons on evolution.
ReplyDelete"Doesn't the existence of evolutionary stasis (including "living fossils") prove that drift - especially drift in genes related to phenotypic variation - is generally not all that important?"
ReplyDeleteNice argument, but stasis does not mean that speciation by cladogenesis is not going on. To fail to observe stasis you would need all populations of the ancestral species replaced or wiped out. According to Niles Eldredge, that is not so easy. The average species lasts millions of years.
This relates to the topic of geographic isolation...bottlenecks, foundation effects...
The "coelocanth" Latimeria is a living representative of the coelocanthiformes but the genus is only known from extant species (there are several other, fossil genera of Latimeriidae). There has been evolution going on there, you know.
divalent says,
ReplyDeleteI can prove none of that for any particular feature, but there is lots of evidence to suggest that animals (including humans) have such mating preferences (e.g., subspecies/varieties prefer to mate within their group when given a choice). So anything that affect outward appears I would presume is likely to be (or at least was before modern times) something that was the focus of sexual selection.
Sh*t. I should have remembered the "sexual selection" argument. It's proven to be a great boon for all adaptationists. They can avoid having to think about their bias by falling back on the good-old "sexual selection" argument.
Let's change the question to maple trees. Look at all the phenotypic variation within a species of maple tree and between closely related species.
Do you think it's all due to adaptation?
OTOH, your job is tougher. To credibly claim it is drift you have to rule out selection at any time from the moment the different allele appeared until it became fixed in the source population.
Strictly speaking, you are correct if I'm required to "prove" that an allele frequency is changing by drift and not selection. But let's not forget that drift is the default hypothesis. If there's no evidence of selection then drift is the most likely explanation.
Have you, or anyone, done this for any allele that underlies any of this "diversity" you speak of?
Most haven't been looked at. If there was selection against certain phenotypes in favor of others (e.g. size of your feet, male pattern baldness, ability to roll your tongue, length of your fingers, shape of your nose, dry ear wax) then we would expect that the alleles would be eliminated quite quickly.
The fact that they have persisted strongly suggests that they are neutral. Indeed, the overall prevalence of phenotypic variation within a population is more consistent with drift than adaptation.
If not, what is the basis for your presumption that "much" of it is due to drift?
Because it's the default explanation. The onus is on the adaptationists to show that most of the phenotypic variation is adaptive.
Heck, they don't even need to prove it. All they have to do is offer reasonable explanations when asked to defend their bias. (Sexual selection isn't a reasonable explanation for most species.)
You are the one making the claim. Back it up with reasons and/or evidence.
Sorry, it doesn't work like that. If you make the positive claim that something is adaptive (or deleterious) then it's up to you to back it up. In the absence of evidence we assume that the allele confers no particular advantage or disadvantage.