“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

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.

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.

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.

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.

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.

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.