ROB SCHMITZ, HOST:
For decades, researchers have studied our earliest mammalian ancestors for clues as to how we evolved socially. The thinking has been that those early mammals were solitary creatures, living, foraging and sleeping primarily on their own. But a new analysis turns that thinking on its head. NPR's Ari Daniel has more.
ARI DANIEL, BYLINE: Go back 65 million years to the end of the Cretaceous, when the dinosaurs' time was nearly up, that comet was about to hit, and our ancestors - small, furry, shrewlike mammals - were scampering about.
CARSTEN SCHRADIN: Nocturnal animals fighting between the dinosaurs.
DANIEL: Carsten Schradin is a behavioral ecologist at the French National Center for Scientific Research. And he says that for the longest time, scientists thought these little mammals were loners.
SCHRADIN: They always had the assumption that our ancestor was solitary living.
DANIEL: But Schradin now believes that assumption is wrong. He and his colleagues spent years sifting through field data from nearly a thousand research articles that describe the social behavior of over 200 primate species.
SCHRADIN: There were monkeys - old-world monkeys, apes. Before people said, OK, this species is always solitary. This one is always pair living. This one is always group living.
DANIEL: But Schradin considered that species can be both solitary and social and worked that range of behaviors into his analysis, all to find out what was the most likely form of social organization of the mammalian ancestor of all these primates. The result...
SCHRADIN: The ancestor was most likely living mostly in pairs.
DANIEL: ...In pairs, which, says Schradin, transforms our understanding of our own heritage.
SCHRADIN: Our ancestors, already millions of years ago, were much more sociable than so far has been believed.
DANIEL: The new findings suggest the potential to pair up goes back a long time and that solitary living may be an adaptation to specific environments. The study appears in the journal PNAS.
NINA JABLONSKI: I love to read, you know, a great paper like this. It's like a little bonbon in the afternoon.
DANIEL: Nina Jablonski is a biological anthropologist emeritus at the Pennsylvania State University. She wasn't involved in the research. She says the paper points out these pairs weren't necessarily monogamous couples, simply two individuals cohabitating.
JABLONSKI: It was probably a physically secure arrangement that helped both of them in foraging, as well as help them both avoid predators of various kinds.
DANIEL: And perhaps, she says, to just keep warm - two furry balls curled up beside one another, generation after generation. Ari Daniel, NPR News. Transcript provided by NPR, Copyright NPR.
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