A new Turkey-based study suggests babies born with ambiguous genitalia might be more common than previously estimated, finding 1.3 in 1000 births recorded as visibly intersex among study participants — nearly double the 1-in-2000 birth rate typically cited.

Intersex refers to a range of chromosomal and hormonal conditions that blur the line between traditional definitions of male and female. Some are internal and have no effect on the appearance of external genitalia; it’s possible to be intersex and never know it. A subset of intersex conditions include so-termed ‘abnormal’ genitalia — genitals that don’t match the sex of internal organs (for instance, a penis paired with internal ovaries) or say, ambiguous genitalia (for instance, a large clitoris that appears more like a small penis).

It’s a finding at the confluence of culture and science.

“Most of the published data is coming from Western countries in which consanguinity rates are lower than our country,” Dr. Banu Kucukemre Aydin, of Istanbul University in Turkey and the study’s first author, said in a statement. Consanguinity, that is, marriage to blood relatives, has been linked to intersex characteristics in babies in other regions where the practice is more customary. The number of babies born visibly intersex in India is unknown, but consanguineous marriage, while decreasing, is believed to currently be more common in India, than in the West.

However, the researchers say the fact that their study included more than 14,000 newborns at birth more accurately records visibly intersex birth rates than studies that have typically relied on birth registries (which may or may not accurately reflect condition at birth).

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Regardless, the study’s findings offer more evidence that a recalibration is required of sex as only either female or male. Without it, guided only by a binary definition of biological sex, society will resort to discriminatory practices — case in point, the recent ruling by the International Association of Athletics Federations that effectively defined female-ness by placing a limit on the amount of testosterone people could naturally produce and still compete as women. It’s a decision widely seen as targeting female two-time Olympic champion Caster Semenya, a woman who is believed to have an intersex condition (though she has never confirmed it). And it is a decision widely perceived as discriminatory — the ruling panel even acknowledged it as such in a statement, though it justified the discrimination as “necessary.”

It’s only necessary if we continue defining sex as only either female or male. Kucukemre and team’s research makes it clear that definition applies to far fewer people than we thought.