[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.