There seems to be something special in the way humans accumulate and refine knowledge over generations that seems to be unique, but this is hard to isolate and test. Maybe it is just that our quantitatively higher intelligence and social nature combines to weirdly to create a qualitative difference.
More or less modern humans existed for hundreds of thousands of years with very little change. The exponential growth of knowledge in the last several thousand years is just a blip on that timeline, and it mostly became possible due to certain breakthroughs like agriculture.
Sure, most animals have significantly less mental capacity than homo sapiens, but I'd argue that the human society is decoupled from the biological capabilities of a single individual to a large degree. It's a separate self-organizing system, and 99% of our perceived intelligence (a made up number) is purely social in nature.
The fact that individual specimens of our species are capable of reflecting, in the first place, on "what makes us what we are", is itself an example of the boundless capacity for abstraction. It is itself a meta-idea. Even earlier humans were able to talk, then pause, reflect and suddenly point out: "we are having a conversation right now". Animals (such as prairie dogs) may have linguistic constructs for various colours; but not for the the abstract idea of "colour", let alone for the abstract idea of "perception". But I agree that there is a second component to this, which is the fact that each new generation starts from the latest abstractions arrived at by the former, then carries on. So what is unique about humans is that this process appears to be boundless, both at the individual and collective level.
