A recent paper by Aaron Blackwell, co-authored by Broom affiliates Ben Trumble, Melanie Martin, and Michael Gurven examines how parasitism affects female fertility of the Tsimane people of Bolivia. Women infected with giant roundworms could bear up to two more children during their lifetime compared with uninfected women, an analysis of nearly a decade of medical data suggests. Hookworms, on the other hand, might act as birth control. Women with these parasites could have three fewer children than uninfected women.

No one knows exactly how worms tweak fertility. The parasites could tinker with immune cell numbers, making conditions ripe (or wrong) for pregnancy.

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