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A golden mole. Photo: killer18

Male golden moles have tiny penises—and reason to worry about that. Females judge potential mates by their penis size, which they use to gauge a male’s attractiveness for copulation. The longer the penis, the BBC writes, the better the male’s chances of impressing females and fathering offspring.

Golden moles are blind creatures that live in underground networks of specially dug tunnels in sub-Saharan Africa. Though they resemble moles, they aren’t closely related to true moles. Their nearest relatives, instead, are small insectivorous mammals, and researchers know little about their reproductive strategies.

The moles live solitary lives but they will mate at any opportunity that presents itself. Females constantly reproduce and, in the dark, use smell and touch to measure the attractiveness of potential partners.

The new study, which appeared in the journal Mammalian Biology, found that golden moles actually have some of the smallest penises per length of body in the mammalian kingdom—about 1.2 to 2.5 mm compared to their 74 to 97 mm-long bodies. But these sizes can vary substantially, much more so than variability in their body length or testes size. The longer the penis, the researchers reasoned, the better its chances of depositing sperm that wins the race to fertilize the females’ eggs.

From a female perspective, males that are able to invest heavily in this trait boast superior genetics. Plus, penis size is an easy way to measure a partner’s attractiveness for blind moles living in dark, cramped tunnels.

Other animals living in dark environments, such as bats in caves or seals in murky waters, may also use penis size in a similar way. Humans, the researchers reassure men everywhere, likely do not judge penis size in the same context, since we employ other pre-copulatory mechanisms for selecting our mate. Once penis size is revealed, they point out, usually the decision to mate has already been made.

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