I think we pretty much all believe that it's our intelligence that separates us from other species. In The Secret of our Success, Joseph Henrich makes the case that we are hardly more intelligent than primates, if at all, across a number of measures. What separates us is our culture.

The arguments Henrich makes are thought-provoking, causing me to question a lot of what I thought I understood. Nevertheless, I already appreciated the main principles of his argument that culture drives natural selection in many ways through its selection of what genes are preferred (and therefore conveyed to the next generations).

Humans are uniquely good at learning, even from those who have died hundreds of years ago. Put someone in a new environment and they will usually die, because they are not smart enough to figure everything out like how to catch/find/cook food and stay safe; but put someone in a new environment having taught them what to do through generations of gradually accumulated knowledge, and they will thrive. Henrich uses history to make arguments that our culture has prioritized learning, which has selected for a species that is now so good at it.

It is a fascinating book.