Science Forums 2

[CraigD]

Originally Posted by charles brough

[Title: the apes evolved but we don't!]

A couple of questions:

• Why do you class human being outside of the apes, specifically the great apes? By every scientific biological classification scheme of which I’m aware, humans are considered great apes (hominidae).
• What is your evidence that apes other than humans (eg: chimpanzees, bonobos, gorillas) have evolved more than human beings. To the best of my knowledge, there is no such evidence. Hominina, (humans being the only surviving species, but only barely, neanderthal having survived until about 24,000 years ago, and the more recently discovered homo floresiensis until as late as 12,000 years ago) actually showing significantly more genetic variety than other apes, though whether this is due to accelerated evolution, as some have proposed, or a much greater population size, remains, I think, an undecided question of some contraversy.

By best present day theory, humans last branched from their closest non-human primate relatives, the panini (bonobos and chimpanzees), around 7-5 million years ago. Considerable physical and apparent cultural variation existed in the many hominina lines between this split and the somewhat arbitrary point 0.2 million years ago marked as the beginning of “anatomically modern human beings”. Although I’ve not studied it in detail, my impression is that evolutionary changes in physical traits are more dramatic among the Hominina than among the panini.

(source: Evolutionary Trees, a rather nice compilation page by Bob Patterson)

In short, I’m aware of no evidence that non-human primate species have evolved more than humans, and of considerable compelling speculation that humans have evolved more than most non-human primates.

Originally Posted by charles brough

Why can't social theorists explain it without coming up with four to eight different conflicting theories?

IMHO, the absence of the same orthodoxy in the social sciences as are found in the physical ones are due to the inexact and subjective nature of social science experiments. It’s appallingly difficult, in the social sciences, to devise an experiment that will reliably prove a particular theory wrong, allowing many contradictory theories to coexists.

However, this question is less relevant to me than what it suggest to me about the overall nature of Charles’s recent ideas concerning evolution. I’ve been puzzled in this thread, and the similar alternative theories thread, How could we have stopped evolving?, by what seemed to me to be Charles’s strange claims about biological evolution (or the lack thereof). This thread appearing in the social sciences, rather than the biology forum, has provided me a clue toward resolving my puzzlement.

Charles, please confirm, clarify, or correct, but I believe your recent claims amount to suggesting that the rapid transition from roughly anatomically modern humans “living pretty much like the animals” (though with tool use exceeding that of modern non-human primates) to living much like modern humans, which appears to have occurred 60,000 - 12,000 years ago, can’t be explained as resulting from genetic evolution processes only. Though this raises the only speculatively answered question of what caused this dramatic transition, I agree, and think most biologists would agree, with this claim.

What I disagree with, and think most biologists would also disagree with, is the suggestion that this “culture explosion” somehow “switched off” the biochemical mechanism of genetic evolution for humans. Although, with the prospect of our modern understanding of molecular biology allowing us to inspect and alter our genome, it may not remain the case even for the next century, I know of no evidence or sound theory that suggests this. Biologically, we humans appear to be evolving much like any other animal, wild or even domestic (whether humans should be classed as wild or domestic animals is an interesting question, though, I think, one for another thread). The visible changes - particularly those made to the landscape and environment - due to this process are dwarfed, however, by those due to change in human culture.

Another remarkable coincidence relevant to this “epigenetic” (note that this is an archaic use of the term which can be confusing to people familiar with modern biology literature) perspective on evolution is the extinction of non-human hominina species around the same time that we began exhibiting modern behavior – that is, stopped “living much like the animals”. A reasonable and common speculation concerning this coincidence is that a critical trait of modern humans is xenophobia, which lead our distant ancestors to either outright exterminate, or at least aggressively outcompete, our closest relatives.

In long-term evolutionary terms, such an event is dramatic: no longer can a selection event occur via a hominina species going extinct, resulting in all future hominina descending from a more limited pool. If humans go extinct, the hominina line is over, and with it, the particular 7-million-year-old evolutionary “experiment” of which we’re the latest result.