Study challenges idea that autism is caused by an overly masculine brain.

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▼ Of the many proposed triggers for autism, one of the most controversial is the “ extreme  male brain” hypothesis. The idea posits that exposure to excess testosterone in the womb wires both men and women to have a hypermasculine view of the world, prioritizing stereotypically male behaviors like building machines over stereotypically female behaviors like empathizing with a friend. Now, a study is raising new doubts about this theory, finding no effect of testosterone on empathy in adult men.
The work does not directly address whether high levels of prenatal testosterone cause autism or lack of empathy. That would require directly sampling the hormone in utero, which can endanger a developing fetus. But the new study’s large size—more than 600 men—makes it more convincing than similar research in the past, which included no more than a few dozen participants, experts say.
The extreme male brain hypothesis was first proposed by psychologist Simon Baron-Cohen at the University of Cambridge in the United Kingdom. In 2001, he and colleagues found that women given a single hefty dose of testosterone fared significantly worse at the Reading the Mind in the Eyes test (RMET), which asked them to gauge the emotional states of others based on their facial expressions. The women’s performance seemed to track with a controversial metric called the 2D:4D ratio, the relative lengths of the second and fourth fingers. Men—and people with autism—tend to have a longer ring finger than index finger, and some researchers believe that is due to higher prenatal exposure to testosterone. ( Others are  skeptical.)
Taken together with the observation that men are at least 10 times more likely to develop autism, Baron-Cohen argued that the condition results from a “masculinization” of the brain in utero.
But as the theory caught on in psychology circles, few seemed to notice that the small follow-up studies that other researchers attempted failed to replicate the original findings, says Amos Nadler, a neuro-economist at the University of Toronto in Canada. “People referred to that original study as if it was a solid stepping stone,” he says. “Pardon my French, but nobody was calling bullshit.”
Nadler and colleagues decided to run a much larger study. They also focused on (▪ ▪ ▪)

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