[jjk166]

Intelligence was evolved millions of years after the most recent common ancestor. Harnessing fire, clothing, etc. came later still. The lineage that would ultimately give rise to humans split from the chimp/bonobo lineage as the human ancestors adapted to savanna life, likely due to aridification brought on by the formation of the Himalayas.

It's possible that selective pressure towards intelligence was greater for the human lineage than for the others. It's also possible that the evolution of intelligence was equally likely across the different lineages and humans just happened to be the one where the mutation happened. Regardless, once human ancestors filled the niche, it would have been difficult for another lineage to get in on the game.

[_AzMoo]

Is there a specific definition for intelligence?

[jjk166]

What definition are you using to say chimps don't have human level intelligence?

By any useful definition, the intelligence of human ancestors very closely resembled that of chimps for about 4 million years after the human and chimp lineages diverged. While it's impossible to say for certain, that's around the time that endocranial volumes started growing consistently beyond the range seen in chimps. That is also around the time of the first evidence of stone tool making.

[dotancohen]

Like life, many sources define it differently.

[dmbche]

Is there a specific definition of definition?

[Arwill]

Substitute orangutans for Australopithecus. That is (one of) the branches that did evolve more intelligence, but didn't survive. I suppose there were lots of such branches, that either merged back into humanity (like the Neanderthals), or died out.

[jjk166]

Australopithecus is essentially on the human branch, and likely was still several million years before the development of advanced intelligence. Our common ancestor with Australopithecus was not any more intelligent than a typical Australopithecus, as far as we can tell.

As far as we can tell, no branch developed significantly increased intelligence after splitting off from our own lineage. That's not to say it definitely didn't happen or that our lineage was always the smartest, just that there isn't any evidence demonstrating a qualitative difference which has survived to the present. But it's weird that no such evidence exists.

Conversely different primate groups did independently evolve similar levels of intelligence, like Capuchin monkeys (which are new world primates) developed their intelligence after splitting off from the old world primates some 40 million years ago. Baboons and Macaques likewise each evolved intelligence independent of the great apes. Likewise similar levels (if different specializations) of intelligence have evolved independently outside the primates, such as cetaceans, elephants, and corvids. For cephalopods, which likewise are highly intelligent, their common ancestor with us didn't even have a brain.