Social intelligence is the most important kind of intelligence.
The most important part of social intelligence is empathy. Empathy underlies all social ability. Empathy is the primary way people connect with others. Connecting with others
People have feelings and thoughts, and they wish for others to relate to them. They want others to know how they think, what they feel, and where they live. Social intelligence is therefore the most directly attractive form of intelligence to those receiving the attentions of anyone blessed with its possession (which means anyone at all).
Since social intelligence is so attractive to others, it potentially connects its possessor to the entire collective resources of humanity (personal, material, and infrastructural resources). In fact, no other form of intelligence has as much connective potential.
So, people are compelled not only to wish to connect with individuals who have a high level of empathic responsiveness, people most admire such individuals. People see such individuals not only as promising an especially enriching inter-personal connection with themselves, but as promising an especially strong connection to (the) collective (resources of) humanity.
The value of social intelligence, and of its underlying empathy, is therefore incalculable, both to the interests of its possessor, and to the wider interests of the world.
But, all this means that social intelligence is the most advanced, most complex, form of intelligence. And, this, in turn, makes social intelligence the most demanding kind of intelligence on the brain. So, given its potential benefits to its possessor, social intelligence tends to win out over all other forms of intelligence in terms of what the brain actually does. In short, social intelligence is largely how the brain works: its underlyng empathy is a central biological imperative.
And, the cognitive structures and functions of empathy are where autism enters the world.