That's what I was thinking too. It seems to me that a certain intelligence might be a requirement for having good social skills, i.e. a good "theory of mind" of individuals around you. Therefore, it would make sense that social skills and intelligence must co-evolve. Total conjecture, of course.

However, octopuses are widely considered the smartest invertebrates, and they are solitary creatures. Hunting also exerts selection pressure for higher intelligence. You still need to predict the actions of other species even if you rarely interact with your own.

The idea here though is that social success is more than just smiling constantly and having a trustworthy face. There's some cunning involved.

People got social by agreeing on a common enemy. To declare social biotope where social skills such as ally building, intrigues and "friendships" exist, the threat of such a common alienation must exist. The hatred and fear where there first.