Falsehoods: Has evolution stopped for humans?

That explanation, of course, points out how we understand things differently than did Darwin and other biologists in the decades following, who didn't know what an allele was.

What's the allele for endosymbiosis?

I think it was Lynn Margulis who raised this objection against equating evolution with allele change, and I also think it's pretty much a show-stopper.

toto: I can't think of a more profound example of change in allele frequency than the combining of two previously distinct genomes.

There is no show stopper here. There is merely the adherence to the trivial and sophistic. Let the show begin.

I think I've only ever heard this argument made from people who mistake our dampening of natural selection for a wholesale stopping of evolution. The only argument that can be made is that we are, through health care and social support structures, keeping alive the more unfortunate parts of society so their genes can theoretically be passed on. This obviously has nothing to do with "stopping" evolution -- just in mitigating some of the selection factors.

the only argument that can be made is that we are, through health care and social support structures, keeping alive the more unfortunate parts of society so their genes can theoretically be passed on.

A falsehood we will also deal with in time!

Nice post, Greg, I really don't have much to add in the way of substance, but a neat little bit about human evolution that you already probably know: lactase persistence allelic frequency in humans makes an excellent example of how humans are, in fact, still evolving. They also demonstrate the historical shift in allelic frequency as well as a strong selective event in Northern Europe for lactase persistence. These allelic frequencies are still changing and will continue to change for quite some time...

A falsehood we will also deal with in time!

Awww. I suppose you want me to eat my peas first.

Let's restate the question about human evolution, and pick a trait that used to have selective advantage but to the extent that it is correctable in industrialized society it isn't very selective anymore: good eyesight.
Should we expect more and more combinations of alleles that allow for poor eyesight to become common or even prevalent over the much smaller number of allowed combinations that allow for good eyesight? Between mutation and drift, how many generations would it take for a noticeable shift to become apparent? Tens? Hundreds?

So I'm still wondering, are we different from the Cro-Magnon in any meaningful ways?

But why is it ONLY a change in allele frequency over time?

Don't changes outside of genes count? Epigenetic changes or changes in DNA switches should count also, shouldn't they?

I can see a case being made for ANY changes in DNA over time being the definition of evolution, including changes in 'superfluous' DNA.

New England Bob: You are absolutely correct. The "change in allele frequency" idea only really works in a world in which genes code for proteins and everything is a protein, and this totally ignores non-genetic transmission.

One person's answer to a fallacy is another person's fallacy.

The contrast in this post is really about phenotypic vs. genetic change. The points you bring up are all to be addressed as well.

Wait...does this tie into the biological v. genetic parent post too? Is this a series? Link them up if they are, please!

It is a series. I'm working on the linking up now..

Okay, and thanks! *sigh* It took me forever to find the bit of the last aricle I was wondering about when paragraph the whichever twigged my brain and told me "maybe you'd better go look back at X..."

Now let's get back to the original question: "Has evolution stopped for humans." I feel like I don't even want to answer that question at this point, don't you agree?

The way I see it, if someone asks you a painfully ignorant question, you can either suck it up and answer it yourself, or let some dumbass with an agenda and no grasp of the topic whatsoever answer it for you.

Brother: I think you may have missed the point by about ten miles...

Brother: I think you may have missed the point by about ten miles...

To be fair, I was letting a stray thought out leak of my head, not commenting on the article.

I can imagine a hypothetical scenario where evolution might stop for a species that is not extinct.

One needs to posit zero variation (every allele is at 100% frequency - it's a population of perfect clones), and a mutation rate of zero (a mechanism for replicating the genetic information that is 100% perfect).

Hard to say how long such a species would actually last in the real and ever changing world, or whether something like a zero mutation rate is even physically possible.

I can't think of a more profound example of change in allele frequency than the combining of two previously distinct genomes.

Then you have a non-standard definition for 'allele'. NTTIAWWT.

Evolution is a change in frequency of heritable features, in general ("feature" here really means anything physical, not just the phenotype - a certain nucleotide at a certain locus is a feature).

Heredity needs not be mediated by genes, in principle. Evolution and natural selection don't care how heredity is mediated, as long as it's actually there. I mentioned endosymbiosis, others have metioned epigenetics. Another striking example is in origins-of-life models, where primitive chemical replicators can maintain some heredity (and thus evolve) without any explicit repository of genetic information. This also occurs in artificial evolutionary systems, which may or may not use a genome, but nevertheless fully utilise the power of evolution by natural selection.

Of course, in practice, in modern lifeforms, almost (almost) all of heredity is mediated by genes, and therefore gene-based evolution represents 99.999% of situations of interest. But it's nice to be able to separate a general principle, from a particular implementation.

YMMV.

I agree with you guys..
http://www.newsguide.us/art-entertainment/movies/Todd-DiRoberto-of-Amer…

It strikes me that change in gene frequency over time is a fairly slow adaptive process. And that we live in a world of very rapid environmental change. Changes in gene-mediated fitness are simply too slow to keep pace. Cultural evolution, rather than changes in gene nature or distribution, is the dominant force in human affairs.

Greg Laden,

>> the only argument that can be made is that we are, through health care and social support structures, keeping alive the more unfortunate parts of society so their genes can theoretically be passed on.

> A falsehood we will also deal with in time!

You don't think the burden of deleterious mutations should probably rise when the variance in the number of surviving children per individual goes down? I won't say it's a fact, but it seems highly likely. I'd be pretty impressed if you could demonstrate that it's definitely false or even just unlikely.

Eric, there are a number of reasons that this is a falsehood, and I'm afraid that one of them is that our system of medical care is deteriorating while the complexity and severity of our medical problems is increasing, so .... the whole argument turns around. But that is not the main reason. Stay tuned.

But what if a gene has two versions, with different DNA sequences, but both DNA sequences code for the same exact protein? Some people would say that there is only one allele, and for all practical purposes, this is OK and will not mess you up, depending on what you are doing with this information.

Couldn't such a situation still have a phenotypic effect? For example, we know that the way genes are expressed in cells is often determined by small molecules such as microRNA's. So theoretically, two alleles with different DNA (and hence corresponding RNA) sequences but coding for the same protein, could be expressed differently in cells if the section where they differ is a binding site for a micoRNA. I don't know if there are any known cases of this, but it seems perfectly plausible to me.

Jon: are we different from the Cro-Magnon in any meaningful ways?

For one, no Cro-Magnon ever could have asked such a question. I am not being facetious: our culture is as much a part of our evolutionary heritage as the DNA, although it is not transmitted in the form of alleles. (It is, at the same time, an essential part of the environment within which the genetic bits evolve, but so is every gene a part of the environment within which each other gene evolves, so that's no distinction.)

This makes trouble for the definition of evolution, unless you enlarge the definition of "alleles" to include cultural phenomena, with some danger of turning the latter into mush. But evolution doesn't care about our definitions; it's for us to try to keep up as best we can. Anyway trying to understand human evolution in isolation from culture is folly.

I wonder if there is something wrong with the way evolution is taught in schools (it's still taught in the USA, isn't it?) When evolution is mentioned people seem to think about the phenotype changes only but don't seem to understand that the process of differentiation of species occurs over unbelievably long periods. We can cross-breed some species with mixed results on the viability and reproductive capacity of the offspring - for example we cross a donkey and mare to get a mule (does anyone still call it an 'ass'?) - anyway, the phenotype changes are obvious and yet the horse and donkey have not differentiated enough that no offspring will be produced.

The other thing about the public perception of evolution, and this is something that really annoys me, is that people imagine that some of our ancestor species are still extant. People have these bizarre notions that the apes developed from the modern monkeys and that humans developed from one of the (other) modern great apes. (And incidentally, people don't seem to realize that humans are one of the great apes.)

So in general, the public's understanding of evolution seems to be screwed up beyond belief. It's no wonder that they easily fall for claims that humans are no longer evolving. Of course for some creationists who pretend to believe in evolution that is the case - modern humans are god's planned species. More sophisticated creationists like Francis Collins might say that human evolution was inevitable but that god may have a plan for further human evolution.

The only place I've seen this argument lately is as a strawman. A swarm of racists (or sockpuppets of one racist) in this Pharyngula thread claim that "leftists" believe "evolution by natural selection somehow stopped for humans 50,000-100,000 years ago" but since this is clearly false, black people are inferior.

moar: I think the "evolution stopped" argument is pretty popular among eugenicists. They feel that with natural selection failing to hold up its end, it's up to them to provide artificial selection to fill the gap.

I confess that as a teenager I thought my myopia was pretty strong support for the first part of the above argument. I reasoned, though, that in no time (geologically speaking) we would have full control of our genomes and could then replace unfortunate alleles directly in our germ plasm, as desired. Eugenicists don't make this connection because it doesn't fit with what they really want to do, which is to practice eugenics, i.e. treat people like farm animals; any external purpose is more or less incidental.

* * *

The "descent with modification" expression is properly not considered a definition, but rather just identifies the circumstances where evolution necessarily occurs. A definition of evolution that depend on alleles is limiting because evolutionary natural selection can occur in circumstances where there is nothing that could be pointed to acting in the role of an allele.

As I see it, "descent with modification" is the unavoidable consequence of evolution, rather than the definition of it.

Eric, if selection pressure is reduced in way such that a greater variation of offspring survive in every generation, the so-called burden of deleterious mutations will not change, because by definition the extra surviving variants would not be deleterious anymore, because the environment has changed and the selection pressure that once made them deleterious is no longer present. (Not to say that these same variants might not once again become deleterious - or even advantageous, when the environment inevitably changes yet again.

moar: This comes directly from the previous paper and book by Henry Harpending and others demonstrating not only post-pleistocene evolution, but suggesting (rightly or wrongly) accelerated evolution in humans. There are some ways to interpret that as suggesting that humans have divided into distinct populations that are becoming increasingly different and that eventually we'll have several species: A low-intelligence dark skinned laboring species that is a little dangeriou, a slanty-eyed yellow highly intelligent species and a white species with exceedingly high moral standards which will enslave the dark species and try very hard to kill off the yellow species before they kill off the whites.

Or something.

Harpending et al are correct in that there is plenty of evolution. I think they have quaint views of both ancient and modern population dynamics, and that's OK because I will correct that by and by, because it takes time. There is a lot of evolutionary change going on in humans (it is impossible to imagine how that would not be the case) although I have not addressed that in this post. I am just now putting the finishing touches on a post that will begin to address it, which will be posted a bit later on this week.

For clarity's sake, can the triple negative in the quote below be simplified to say the following?

This does not mean that I don't think meaningful, adaptive change is not happening now with humans.

Regarding the actual meat of the article, I think a good case has been made for the fact that asking whether we've stopped passing on mutations is like asking whether the Earth has stopped spinning.

But, when people ask if evolution has stopped for humans, I don't think they're really asking if we've stopped passing on mutations. In colloquial verbiage, the question is really asking whether we've removed certain selective pressures, to our detriment or to stunting of our development.

In other words, the concern of the question is in whether we as a population are more vulnerable to phenotypic degradation now that nature is less able to burden the phenotypically "unfit" to the point of reduced reproductive success, and whether beneficial alterations have a fighting chance to proliferate.

Needless to say that the question has no simple answers, so I look forward to the next instalment.

I recently read an article explaining that synonymous mutations can sometimes affect the phenotype by altering the splicing of mRNA. I can't remember where it was, unfortunately.

I've heard people claim that, due to increased health care, etc... natural selection doesn't apply to humans anymore. My reaction always is that he (or she) comes from that one sperm cell which beat several million others to the egg. That's quite some selection.

I enjoyed the post and agree with it, but I would like to point out (what I believe is) a mistake.

"If we measure phenotypic change in humans over time and see some change, then that must mean we are evolving." Not necessarily. Phenotypic changes can be caused by environmental or cultural changes. An example would be the increased height of Americans over the past hundred years.

Thanks!

Ernie