In the womb, a brother's hormones can shape a sister's future
When siblings share a womb, sex hormones from a male fetus can cause lasting changes in a female littermate. This effect exists for all kinds of mammals — perhaps humans too.
by Jon Hamilton
Apr 09, 2024
3 minutes
The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health all the way down to our very molecules. We'll be sharing these stories over the next several weeks.
A sibling can change your life — even before you're born.
That's because when males and females share a womb, sex hormones from one fetus can cause lasting changes in the others.
It's called the , or intrauterine position effects, and different versions of it have
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