Female moles evolved to have high testosterone levels, making them fiercer diggers and mothers. Female hyenas share this trait, but it means they must give birth through a male-like phallus.
A new finding in mice rewrites the textbook explanation of the male sex-determining gene, Sry. It might also help us better understand how males and females come to be.
Parkinson's disease is twice as common in men than in women. A sex gene called SRY, found only in men, could go some way to explaining this – and might pave the way for potential treatments.
What produces the differences between men and women? Are they trivial or profound? Are they genetic or environmental, or both? And are men really closer genetically to chimpanzees than to women?