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Surprise! Male and female brains are the same

“Sex differences in the brain are tiny and inconsistent, once individuals’ head size is accounted for,” says new research.

Surprise! Male and female brains are the same
[Image: Jolygon/iStock]
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If you thought that the brains of men and women are inexorably different, you are wrong. “The truth is that there are no universal brain features that differ between the sexes,” noted Lise Eliot, a neuroscientist at Rosalind Franklin University, in a news release. “The brain is like other organs, such as the heart and kidneys, which are similar enough to be transplanted between women and men quite successfully,”

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She is confident of this because she is the lead author of a just-published giant review study in Neuroscience and Biobehavioral Reviews, which analyzed hundreds of major of MRI and postmortem studies over three decades. She found that men’s brains are 11% bigger on average. This is in proportion to their body size, which shifts ratios like gray versus white matter. But sex or gender explains only a tiny proportion (1%) of variation. “Men and women’s brains do differ slightly, but the key finding is that these distinctions are due to brain size, not sex or gender.

“Sex differences in the brain are tiny and inconsistent, once individuals’ head size is accounted for,” Eliot points out. And importantly, “none of these size-related differences can account for familiar behavioral differences between men and women, such as empathy or spatial skills.”

For this research, a quartet of academics tracked measures of 13 supposed anatomical differences through hundreds of studies. They found wide differences among brain measures from study to study—concluding that the studies showing supposed differences are, in wider context, inaccurate. They are not the first to conclude that men and women have the same gear under the hood, though this study is notable for its size and breadth.

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They also disproved the longstanding belief that women’s brain hemispheres are somehow more well-connected than men’s, which supposedly leads to stronger left/right brain communication. This is false.

“The handful of features that do differ most reliably are quite small in magnitude,” says Eliot. Consider the amygdala, “an olive-sized part of the temporal lobe that is important for social-emotional behaviors.” How much bigger is it in men? One percent.