Darwin wrote very little about human intelligence or the place of our species in evolution. He didn't really need to. If his revolutionary idea was true for the rest of the plant and animal kingdom, it would have to apply to humans as well. But while genes and evolution may have been the process that led to the development of the human mind, a very important part of the story is what we did with that mind as soon as we had it. And the very first thing we did was to create culture.
Culture is about sharing information, about sharing models of the world.
It is something that so far only humans do, and all humans do it. Culture is so powerful that it transcends anything our genes are telling us. Culture is the reason we have managed to condem so many generations of young men to risk their lives and reproductive success in one war or another. In Darwinian terms, it doesn't pay to die for your country unless you have already reproduced. Strangely, no-one in the AI community ever talks about computers having culture.