Human brains do not fit neatly into 'male' and 'female' categories but share a mix of male and female features, a study led by an Israeli researcher from Tel Aviv University said.
"It's very, very rare to find someone who has only masculine or only feminine characteristics and it's much more common to find people who have both masculine and feminine characteristics," said Professor Daphna Joel from the Tel Aviv University School of Psychological Sciences and Sagol School of Neuroscience.
Professor Joel, who led the group of researchers, set out to study whether the differences between male and female brains added up to create two distinct brains, either male or female.
She concluded that while genitals in almost all humans come in two types, human brains do not and are not distinctly male or female.
Furthermore, the binary assumption that if you are a female or a male it implies certain behaviours, character traits and attitudes have no scientific basis, Professor Joel said.
The research published in the Proceedings of the National Academy of Sciences (PNAS) was based on an analysis of magnetic resonance images (MRI) of more than 1,400 human brains. They showed that brains vary in their composition, regardless of their gender.
In the study, researchers defined a "male" zone and a "female" zone for each region of the brain based on data sets.
They found that many more individuals had brains with both "male" and "female" features than people with only "female" or only "male" brain features.
On a group level, differences between male and females may be observed, but on the individual level it is very rare to find someone who has only masculine or only feminine characteristics.
The study, Professor Joel said, supports the idea that gender is non-binary and suggests that society "should stop treating people according to the form of their genitals and start treating people according to their specific characteristics and interests."
That concept in particular is receiving the attention of Hollywood in the new movie "The Danish Girl" which stars Oscar-winning British actor Eddie Redmayne and tells the story of 1920s transsexual pioneer Lili Elbe.
"What I learned from this experience is that gender is fluid in the way that sexuality is fluid and we have bits of everything in us," Redmayne said in a promotional interview about the movie.
Professor Joel said she envisions a future where people are not so routinely classified on gender alone.
"Our assumption as a society that our sex category whether we have male or female genitals has implications to what we would love, what we would like to do and what type of person we will be that also people come in two types, male nature and female nature, this has no scientific basis and people are very different from each other so I try to move from the language of the two sexes are similar or different, to language which means we are all different," she said.