[Reproduced from NATURE | NEWS, 13 June 2012;
Nature doi:10.1038/nature.2012.10822]
'Hippie chimp' genome sequenced
Genetic sequence could solve mystery of why bonobos are more peaceful than other
When the Congo River in central Africa formed, a group of apes was forever stranded on its southern banks. Two million years later, the descendants of these apes — the
bonobos — have developed distinct social patterns. Unlike their chimpanzee relatives on the northern shore, they shun violent male dominance and instead
forge bonds through food-sharing, play and casual sex.
Unlike common chimpanzees,
Pan troglodytes, bonobos,
Pan paniscus, seem to use sex to resolve disputes.
An 18-year-old female named Ulindi has now become the first bonobo,
Pan paniscus, to have its genome sequenced. Scientists hope that the information gleaned will explain the stark behavioural differences between bonobos and common chimpanzees,
Pan troglodytes, and help to identify the genetic changes that set humans apart from other apes.
Distant relatives
Humans, chimps and bonobos all share a common ancestor that lived about 6 million years ago in Africa, when the human lineage splintered off. By the time that our
Homo erectus ancestors were roaming the African savannah 2 million to 1.5 million years ago, populations of the common ancestor of chimpanzees and bonobos had been separated by the Congo River.
The main result, published in, NATURE (2012) doi:10.1038/nature11128, was:
On average, the two alleles in single-copy, autosomal regions in the Ulindi genome are approximately 99.9% identical to each other, 99.6% identical to corresponding sequences in the chimpanzee genome and 98.7% identical to corresponding sequences in the human genome. Little and probably no interbreeding has occurred since then, says Kay Prüfer, a bioinformatician at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the sequencing study. Comparisons of the bonobo genome and sequences of chimps from various populations showed that chimps living just across the Congo River were no more closely related to bonobos than were populations living as far away as Côte d’Ivoire. That implies that the separation was quick and permanent, says Prüfer.
Once the ancestors of bonobos had been separated from those of chimpanzees, they may have found themselves in a very different ecological world. North of the Congo River, the ranges of chimpanzees and gorillas overlap, so those animals compete for food. But no gorillas live south of the river, so bonobos face much less food competition, says Victoria Wobber, a comparative psychologist at Harvard University in Cambridge, Massachusetts, who has worked with bonobos including Ulindi.
In the absence of competition, the ancestors of bonobos may have been free to forage a wider range of foods in large groups, and share the spoils freely. “When food is more consistently available, a lot of the aggression you see in chimps, you don’t need anymore,” says Wobber.
Bonobos also treat sex as casually as a handshake, earning them the nickname ‘hippie chimps’. The sex is often non-procreative and can occur between pairs of the same sex. Chimps tend to have sex only when females are in estrous. “Instead of resolving their disputes aggressively, maybe they’re resolving them with sex,” says Wobber. And whereas chimpanzee groups are dominated by hyper-aggressive males,
bonobo groups are less hierarchical and are often headed by females.
Genetic discrepancies between chimps and bonobos must be involved in these behavioural differences, says Prüfer. But identifying which genetic changes are involved and how they influence behaviour will take time.
However, the sequence of a single bonobo is not enough, says Varki. Other bonobos may share different genomic regions with humans, and these genes would be missed by relying on a single bonobo sequence. Varki says that researchers are planning to sequence the genomes of dozens more bonobos, chimps and gorillas to fill the gaps.
And Ulindi may not be representative of most bonobos in behaviour, either. Wobber has noticed vast behavioural differences in her work with bonobos, and says that the genomic model of the hippie chimp isn’t a peacenik. Ulindi sometimes lashed out at Wobber. “She’s just a mean bonobo. That’s my own personal experience with her,” says Wobber. “I might have picked a different one to sample.”
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Location:OUR CLOSEST COUSIN: BONOBO, THE 'HIPPIE CHIMP'
