William Sidis's IQ is estimated to be between 250 and 300. For a comparison of just how high this IQ is, the middle-of-the-road IQ is considered to be 100. Bobby Fischer the Chess Master has an IQ of 187, Galileo Galilei of 185, and Charles Darwin and Wolfgang Mozart both had an IQ of 165.

At 18 months Sidis could read the New York Times, at 2 he taught himself Latin, and at 3 he learned Greek. By the time he was an adult he could speak more than 40 languages and dialects. He was accepted into Harvard at 11. In his first year he gave a lecture at the Harvard Mathematical Club on four-dimensional bodies, and graduated cum laude at 16; he then proceeded to become the youngest professor in history. Soon afterwards, however, he quit his professorship and spent the rest of his life working menial jobs and trying not to be smart. He vowed never to think of mathematics again. He attempted (though ultimately failed) to become a normal human being. Sidis was hindered, however, because he found the concept of beauty unfathomable, and the idea of sex repulsive. At the age of 15 Sidis took a vow of celibacy (in college, no less), which he apparently kept till his death at the age of 46.

What could have happened to Sidis to make him leave behind his life and abandon the achievements he could have accompished? Perhaps it was being forced to perform and excel by his parents at a young age: his childhood was lost. Perhaps he was unable to find people he could effectively communicate with. After all, many psychologists believe that once someone has an IQ difference of above 30 from you, they're effectively in a different communication range. How must it have been for Sidis, whose IQ of >250 must have prohibited him from communicating with practically everyone? Or maybe as an article in the Prometheus Society's (a society of people with very hi IQs, more exclusive than Mensa) magazine, the Gift of Fire states:

"Aldous Huxley once wrote: 'Perhaps men of genius are the only true men. In all the history of the race there have been only a few thousand real men. And the rest of us--what are we? Teachable animals. Without the help of the real man, we should have found out almost nothing at all. Almost all the ideas with which we are familiar could never have occurred to minds like ours. Plant the seeds there and they will grow; but our minds could never spontaneously have generated them.' And so we see that the explanation for the Sidis tragedy is simple. Sidis was a feral child; a true man born into a world filled with animals--a world filled with us."