“If we didn’t have these social groups evolving in primates, we wouldn’t have the scaffolding in place for humans to build upon,”
Teaming up this way may have been prompted by a switch from a nocturnal lifestyle to moving about in the sunshine. “Being active during the day would have allowed primates to travel across larger spaces and exploit their environment more effectively, but it would have also exposed them to a huge predation risk,” says Shultz. To make it through the day, primates would have needed a new defense strategy to deal with both a greater number of predators and also new kinds of hunters.
“What’s going to nail you at night is different than what’s going to nail you during the day,” says primatologist Anthony Di Fiore of the University of Texas at Austin, who was not involved in the study. It’s tough to hide from eagle eyes in the daytime, but by joining up and serving as lookouts for each other primates would have given themselves a better chance of spotting and evading a swooping bird or other predator.