Big brains come with big social groups in whales and dolphins
arstechnica.com
arstechnica.com
I've never seen any research that backs this up, but I'd love to read some more about these claims. If anyone cares to elaborate?
And you'd be surprised about how little we know about animal intelligence. You should look into the psychology professor Irene Pepperberg and her parrot Alex (Source: https://en.m.wikipedia.org/wiki/Irene_Pepperberg). Fascinating.
Anyway, here's an interesting datapoint: there's something called "domestication syndrome", basically a set of traits that is common to diverse animals that have adapted to humans, from goldfish to cattle. One of those traits is reduced brain size. And the loss in brain size is more pronounced in social animals (dogs), compared to psychopathic loner species like cats. (No idea about goldfish. Really have to read up on goldfish sociology.)
The causality, per evolutionary theory, must obviously be "randomly larger brain" -> "better ability to cooperate" -> "increased survival". The other way around is Lamarckian Evolutions, which doesn't happen.
The smartest peers mate with the females.