To see why, consider the human kind we call dyslexic. At the psychological and social level of analysis, dyslexics are the real human kind; they’re schoolchildren (and adults) who don’t perceive words as most people do. The condition was first described at the end of nineteenth century as a form of “word blindness.” Today’s view is that dyslexic is a consequence of the way brain interpret phonemes, the chunks of sound that are building blocks of words.

Dyslexia, like almost all traits, must result from interactions among many different genes. Nonetheless, one need not know which genes in order to figure out how important heredity is to the condition. Research began in the 1950s, with comparisons of fraternal and identical twins and more recent statistical studies suggest that part of what makes dyslexia happens is a consequence of inheritance. ~ Page 292