Anthropologists ask themselves this question on occasion because it differentiates (in the more classical analyses) between people and other animals, usually other primates. Human brains are about three times the size of a chimp’s, and in the last two or so million years it’s had quite the growth spurt. Since then, our biggest triumph has been in information synthesis; i.e., putting things together, using symbols to represent other things, using what you’ve learned from one problem to solve another. How good you are at this is a measure of intelligence (old school IQ sense).
Social “intelligence” is a prime example of real-world problem solving. Let’s remember that early Homo did not take the SAT’s, at least as far as we know. Our forebears, however, were greatly concerned with coordinating successful hunting expeditions, making arrangements for who should marry whom in order to produce the maximum payoff, and other such survival-related puzzles. Modern people who live in traditional societies may not have “leaders” in the sense that we think of them, i.e., a guy who tells other guys what to do, but there may be a sensible individual who knows everyone in the village and who can, without stepping on toes, help things run smoothly by employing a non-huffy attitude and a little clever manipulativeness. The huffy ones get smacked down. For fun, read “Christmas in the Kalahari” for an example of how this can happen.
Times have changed of course. Now we send our kids off to school, in theory at least to arm them for future problems, and to equip them for reality and survival in context. School, and tests in school, are designed to measure their “potential” in this context. Sure, a kid who does well throughout school may have potential, but it’s useless and not precisely “intelligence” unless he can put it to use to support himself later. It’s like having a hammer but nothing to build. It’s not synthetic, because he didn’t use his skills to help him cope with his environment.
The kids who were leaders, getting by on C’s while dominating their cliques with an air of effortless, laid-back contentment, may well have more intelligence in the early Homo sense than the Mathlete. And if they were attractive (and they usually were), so much the better. Intelligence is what helps humans to survive, and what helps humans to survive (lets get real) are social skills in their appropriate cultural context, not mathematical prowess except in some pretty unusual situations, like Western culture. Attractive individuals who have got those social skills nailed down are better equipped to land jobs, to keep those jobs through manipulation of their coworkers, boss or underlings, and more likely to slip through the radar that filters out those who are not “One Of Us” and get admitted as one of the crowd, where they can affect policy, institute rules, and gain status, money and power. It enables them to score with the best mates and pass on their “winner” culture to their kids. That’s intelligent synthesis - using your native gifts to an end that will help you survive.
We live in a peculiar society that worships “school ability”. But school is just practice. Mathletes are intelligent if they can put their prowess to use in the marketplace and better survive. But not if they end up taking tickets at Loews because they’re so depressed about being pimply and disliked.