The evolution blogosphere this week is concerned about David Attenborough's claim that humans have stopped evolving. Barbara King’s NPR story is a good place to jump into the fray.
But Attenborough is not the first well-known proponent of evolutionary theory to volunteer incautious comments regarding whether or not human evolution continues. Well-known paleoanthropologist Ian Tattersall suggests that human evolution may have stopped. In an interview with Science Friday on April 6, 2012, Tattersall claims: “A population the size of ours has simply too much genetic inertia to change. So I think that as long as demographic circumstances remain the same as they are today, Homo sapiens is going nowhere.”
To put this quotation in context, I provide the transcript below. Tattersall is more cautious and less inflammatory than Attenborough. Attenborough adamantly claims that evolution has been halted by human manipulation. In contrast, Tattersall blames “genetic inertia,” an unintentional outcome of high-density, high-contact populations. Nevertheless, when asked pointedly why evolution has stopped, Tattersall might have sensed a red flag signaling an urgent need to explain that he held no such view. Instead, Tattersall more or less repeats the claim.
The discussion starts at 13 minutes, 13 seconds into the program. Host Ira Flatow is taking questions from the live audience…
FLATOW: Let's go to a question in the audience. Yes, sir.
UNIDENTIFIED MAN: Hi. I was reading an article a while ago that was talking about whether humans will no longer have to evolve because we don't need to adjust to nature anymore because we are adjusting nature ourselves. I was wondering, what's your take on that?
TATTERSALL: Well, I think, first of all, that the human ability to accommodate to the environment culturally meant we could go to many more different areas of the world than we would otherwise have been able to do. And therefore, we're more subject to fragmentation of our population by environmental change. That's one thing. And we evolved in this kind of, sort of, unsettled environmental picture. And human beings for the - or human precursors for the - virtually all of hominid history, have been thinly spread over the landscape.
They have lived in very small densities, in very small groups, moving over large swaths of territory, which again, gives you good circumstances for isolation and evolutionary innovation. Since 10,000 years ago when our species became sedentary, settled down, first started living in villages, then towns and now in urban settings, our population has become huge. Our population is seven billion and increasing, and we're packed, cheek by jowl, over the surface of the Earth.
And these are circumstances in which you could not imagine that significant new genetic innovations could become fixed. Population, the size of ours, is simply - has simply too much genetic inertia to change. So I think as long as demographic circumstances remain the same as they are today, Homo sapiens is going nowhere.
FLATOW: Well, what is the mechanism that's preventing that exactly? You say we're bunched together. There are too many people together. Why is the - why does that stop evolution?
TATTERSALL: It's extremely difficult to get the fixation of any genetic novelty arising in a very, very big population. To get the fixation of genetic novelties which arise spontaneously in populations, you really need to have a small unstable gene pool that can react to this kind of circumstance.
[End of transcript excerpt]
King notes that Attenborough may be something of a loose canon, someone who “has not always aligned himself with credible science.” Tattersall is a responsible writer and credible scientist. I like to think Tattersall would welcome the chance to revise and resubmit his comments about how and why human evolution has stalled. Here he proves to be surprisingly incautious, even by the standards of informal discourse associated with live interviews. Perhaps he really does believe what he says.