Bonobo genome reveals more promiscuity in human past

Michael Marshall, environment reporter

Ulindi from Zoo Leipzig: the lucky bonobo who had her genome sequenced (Image: Michael Seres)

We have now read the genomes of our two closest relatives. The bonobo genome is published today, seven years after the chimpanzee genome was completed.

By comparing the human genome with that of chimps and bonobos, we can find out about the last common ancestor of the three species, says lead author Svante P??bo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

That's a crucial question, because bonobos and chimps live in strikingly different societies. Bonobo society is female-dominated and remarkably peaceful, whereas chimpanzee society is male-dominated and far more aggressive. Which of these is the ancestral state?

Humans split from chimps and bonobos around 4.5 million years ago, and chimps and bonobos then separated around a million years ago.

We don't yet know what the common ancestor of humans, chimps and bonobos looked like, but we do now have an idea of how many of them there were. By comparing the levels of genetic diversity in the three species, P??bo estimates that the ancestral population numbered about 45,000 individuals.

The bonobo genome shows no sign that genes were passed between bonobos and chimps after they separated, suggesting that the two species split completely and did not carry on interbreeding. It may be that they were cut off from each other when the Congo River formed, allowing them to evolve separately.

That's not what happened at the earlier split, when humans broke away from chimps and bonobos. P??bo's analysis shows that more than 3 per cent of the human genome is more closely related to chimps and bonobos than chimps and bonobos are to each other - suggesting that our ancestors carried out interbreeding with apes for a while.

A similar result emerged from the gorilla genome, released earlier this year. The ancestors of gorillas split from the other great apes around 10 million years ago, but interbred with the ancestors of humans and chimps.

These findings add to the evidence that apes and hominins have a tangled ancestry. Modern humans interbred with at least two related species, Neanderthals and Denisovans, and it seems that, millions of years earlier, their ancestors also interbred with apes.

Journal reference: Nature, DOI: 10.1038/nature11128

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