Chimp puberty helps recalculate when chimps and humans split

A chimp in Leipzig Zoo contemplates its mutation rate. (credit: Thomas Lersch)

Genetic evidence is an incredibly useful tool for understanding evolutionary history. It has helped us build up our current picture of how humans migrated out of Africa, and also estimate when chimps and humans parted ways from our last common ancestor.

Estimates that used different methods have placed the chimp-human split anywhere from 3 million to 10 million years ago (mya), sometimes falling far from the estimated 6-7 mya suggested by the fossil record—an indication that something is wrong in the calculations. But as researchers improve their techniques, the estimates are revised over and over again, each time hopefully getting closer to real picture.

Having the dates provided by the fossil record match the genetic evidence would help us to be more sure of our understanding, so it’s important to try to work out where the mismatch is and why it’s happening. Two researchers at Columbia University, Guy Amster and Guy Sella, have suggested an important factor that has been missing: the timing of life events like puberty and reproduction, and their effects on genetics. By building these factors into their calculations, they’ve come up with an estimate for the split that more closely matches the fossil records—around 6 mya.

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