The current thread, Does neutral evolution explain the genetic differences between humans and chimpanzees, is limited to scientists, and I do not wish to go off on a tangent there. One of the concepts which has been expressed there, however, seems to me very naive.
Clearly, humans could and do live in the same environment that chimpanzees do and achieve far larger populations. In fact, one of the reason that chimpanzees might go extinct is human encroachment on the chimpanzee environment. That is classic Darwinian competition. So, how many beneficial mutations do you think it required for humans to get in this evolutionary position?
You’ve claimed that you can account for most of the genetic differences between humans and chimpanzees using neutral evolution but there are now over 7 billion humans and only 300,000 chimpanzees.
There have been a number of effective replies in that thread challenging and qualifying the idea that population size correlates to fitness, but I think the concept is worth exploring a bit further.
Natural selection and ecological limits on population dynamics in the wild may be analyzed in terms of the adaptation of an organism to its environment. I do not see how such constraints apply to humans, because of one glaringly obvious distinction between humans and the rest of the animal kingdom. Whatever the proportion of neutral and beneficial mutation led to the threshold of abstract thought and verbal communication, once these were in place, the limitations of natural selection had to be modified as applied to humans; this for the fundamental reason that we are able to live under circumstances and in places for which we are not physiologically equipped.
No other creature can claim this. Too cold, too hot, too dry, too wet, these we can approach as problems to be solved. We do not need to grow winter hair, we can wear the skin of other beasts. We can build shelters and change our environment like beavers, but unlike beavers we are not a one trick wonder; as required we can build shelters of snow and hide and eventually concrete and glass. Despite our physiology, we can go from the bottom of the Mariana Trench to the moon.
This disconnect between physiology and environment is something new. It is emergent, in that the phenomena is coherent with the fundamental laws which gave rise, but the subsequent behavior cannot be fully explained by reduction only to those fundamental laws. Whatever its initial state, it takes on a life of its own from there. The ability for human cognition to overcome physiological limitations and coordinate activity of city state populations represents a basic discontinuity in nature. If there was a correlation between fitness and population prior, that must be reexamined.