[Symmetry]

What makes primates special, among mammals, is that the number of neurons in our brains scales linearly with brain volume like birds instead of like the 3/4 power of volume like other mammals. See Suzana Herculano-Houzel's work on the topic.

What makes humans special among mammals, other than our big brains, is that we're very good at learning from each other. A 2 year old human isn't really much better at solving mechanical puzzles than a 2 year old monkey but that human is a positive genius at social learning compared to the monkey. And once that human learns a word like "or" they can start applying the disjunctive syllogism in ways a monkey will never match. A large plastic brain probably limits how smart a human can get but it's seemingly hardwired traits like an infants preferences for learning from people with accents similar to their mothers that kickstart humans. See Joseph Henrich's work.

[posterboy]

It's not a hard-wired trait that they cannot do something (i.e. preferentially learn foreign accents or however you would positively describe that).

And it's not exactly an advantagevthat once crystalized, my speach is pretty much incapable of adapting to Russian or anything more foreign.