Essence of g

Scientists search for the biology of smarts

Nearly a century ago, British psychologist Charles Spearman started what remains one of the most passionate debates about people’s mental abilities. Spearman declared in 1904 that he had found the way to measure an individual’s core intelligence. Using a mathematical method called factor analysis, Spearman noted that individuals score similarly on many items from a range of mental tests, some resembling today’s IQ tests.