You know that phrase "think like a man"? According to a new study, it means absolutely nothing.

In 2014, researchers found some physical differences between men's and women's brains — specifically that men's brains on average are larger in volume. But new research, published in October in the Proceedings of the National Academy of Sciences, concluded that despite the size discrepancy, there's no functional difference between men's and women's brains. "Male" brains and "female" brains simply don't exist. In fact, both men and women display brain "features" of the opposite sex.

Perhaps "Men Are From Mars, Women Are From Venus" is a myth we can finally put to bed.

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The study: Performed by Daphna Joel at the Tel Aviv University in Israel and her colleagues, the PNAS study used MRI brain scans to identify variations in brain region size in 1,400 people between 13 and 85 years old.

They found that 29 brain regions differed in size, including areas responsible for memory and assessing risk.

Between 0% and 8% of people had fully "male" or fully "female" brains — and 35% showed "substantial variability," meaning there are male traits in some brain regions and female traits in others.

The brain is a "mosaic" of features. It can't be distinctly categorized and pigeonholed by gender.

Why these results matter: According to Michael Bloomfield, a psychiatrist at University College London, looking at the gender type of a brain shines light on a tricky subject: mental illness. As Bloomfield told the Guardian, while there's no evidence of a gender-specific "type" of brain, there are still mental illnesses that are more prevalent in one sex versus the other.

"We still don't understand why this is," he told the Guardian. "Understanding this could well help us understand some of the biological mechanisms that give rise to these illnesses, which could then enable the development of better targeted treatments."

But unless one brain exhibits "all-male" or "all-female" traits, pegging neurological illness to one gender or the other is difficult.

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"Analyses of internal consistency reveal that brains with features that are consistently at one end of the 'maleness-femaleness' continuum are rare," Joel's team wrote in the study. The brain, as Joel's team sees it, is a "mosaic" of features, not something that can be distinctly categorized and pigeonholed by gender.

It's a major shortcoming that society often views men and women as being wired differently, as Margaret McCarthy, a professor of pharmacology at the University of Maryland in Baltimore, told New Scientist.

"People get wedded to the idea that being male or female is highly predictive of having different aptitudes or career choices," McCarthy said. "This study fights against the idea that these outcomes are based on biological differences, as opposed to cultural expectations."