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.
Moles live a tough life underground. As a result, they’ve evolved helpful adaptations, such as excavator-like claws. Female moles in particular have evolved an unusual strategy: high levels of the male hormone testosterone.
This is an evolutionary advantage. It produces stronger muscles for digging and foraging and aggression, to help mothers defend themselves and their young.
Most of the year, female moles look and behave like males. They have masculinized genitals, with no external vagina and an enlarged clitoris. But when mating season comes, testosterone levels drop and a vagina is formed; mating and birth follow.
How they accomplish this remained a mystery for a long time. But now, the complete sequencing of the mole genome has revealed the genetic tweaks underpinning this strange cycle in female moles, by which reproductive organs (gonads) develop and hormones are produced.