"Our recent research suggests that twins were actually the norm much further back in primate evolution, rather than an unusual occurrence worthy of note. Despite the fact that almost all primates today, including people, usually give birth to just one baby, our most recent common ancestor, which roamed North America about 60 million years ago, likely gave birth to twins as the standard.
"We have been researching the evolution of primate litter size – how many babies grow during each pregnancy – for the past several years. To study mammal evolution and reproductive life history, we use skeletal collections, both fossil and recently living.
"In addition to being an anthropologist, one of us (Tesla) is the mother of twin girls. That’s led to a personal and not just scientific interest in this topic: When did twin pregnancies become uncommon?"
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