Originally Posted by sapeye
Yes, I understand that, but whether at the population level or the genetic level, it's still natural selection, isn't it?
It's less directly natural selection. Consider a trait T that we have but that Neanderthals don't. If you go back 100,000 years, there were moderns and Neanderthals. The moderns had T, but the Neanderthals didn't. Sometime between then and now, T became universal among all hominids.
Suppose that we killed off all of the Neanderthals. Does that mean that T became universal through natural selection of T
? Not necessarily. It was natural selection only if
T itself helped us to kill off the Neanderthals. But it's hard to see, e.g. how a lack of an occipital bun would help us to kill them off.
On the other hand, suppose that T helps its host have more children. Then, in each generation, a greater proportion of the population will have T, including the descendants of Neanderthals
. The spread of T will then really be a result of natural selection, not just free-riding.