From Ed Yong
In Kibale National Park, Uganda, female chimps have taken to carrying sticks around with them. There’s nothing obviously unusual about that – chimps are clever tool-users, who use sticks as probes, projectiles and spears. But these chimps aren’t doing very much with their sticks – they simply hold and cradle them while they go about their usual business.
Sonya Kahlenberg and Richard Wrangham think they know why. They suggest that the stick-carrying chimps are playing at being mothers. Their sticks are the chimp equivalents of human dolls and the chimps treat them like pretend infants.
Kahlenberg and Wrangham present plenty of evidence to make this case, but their final suggestion—that this could be evidence of something that existed be humans split from chimps
—is more of a leap. It is possible. But it's also possible that even if the two scientists are right about what the behavior means, it could have evolved separately in chimps in the time since the split. For more detail about all of this, check out the rest of Ed's post
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