One thing I've learned by following a link from elsewhere in this thread is that while the total count of neurons in an animal's nervous system is not a good proxy for intelligence, the count of neurons in the forebrain is. By that measure, only the orca ranks higher than humans [1].

That doesn't mean language ability is a natural outcome of crossing a certain threshold of brain complexity; if anything it's more likely the other way around: this complexity being be driven by highly social behavior and communication.

1. https://en.wikipedia.org/wiki/List_of_animals_by_number_of_n...