The Blank Slate: The Modern Denial of Human Nature

by Steven Pinker

schizophrenia is highly concordant within pairs of identical twins, who share all their DNA and most of their environment, but far less concordant within pairs of fraternal twins, who share only half their DNA (of the DNA that varies in the population) and most of their environment. The trick question could be asked—and would have the same answer—for virtually every cognitive and emotional disorder or difference ever observed. Autism, dyslexia, language delay, language impairment, learning disability, left-handedness, major depressions, bipolar illness, obsessive-compulsive disorder, sexual orientation, and many other conditions run in families, are more concordant in identical than in fraternal twins, are better predicted by people’s biological relatives than by their adoptive relatives, and are poorly predicted by any measurable feature of the environment. 42