A groundbreaking long-term study of wild chimpanzees suggests that lethal territorial clashes may boost reproductive success — offering new clues into the evolutionary roots of human warfare.
According to atelegraph.co.uk, After monitoring chimp communities for more than three decades, researchers found that birth rates nearly doubled in the years following a successful territorial takeover, raising fresh questions about how conflict may have shaped human behavior.
The study was carried out on the Ngogo chimpanzees of Uganda’s Kibale National Park, which are notorious for violent clashes with neighbouring groups, often resulting in deaths, a phenomenon sometimes described as “chimpanzee warfare”.
Following a series of co-ordinated attacks that claimed at least 21 lives, the Ngogo group’s territory grew by 22 per cent. In the following years females gave birth more often, and their infants were much more likely to survive.
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In the three years preceding the territorial expansion, Ngogo females gave birth to 15 offspring. In the three years after, they gave birth to 37 – more than doubling their fertility rate. Infant survival also improved dramatically, from a 41 per cent chance of death before the age of three to 8 per cent afterwards.
“These findings help us understand why chimpanzees, and perhaps our own early ancestors, evolved a capacity for co-ordinated violence,” said Dr Brian Wood, of the University of California, Los Angeles. “When food is scarce, territorial gains can translate into real reproductive advantages.
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“Humans have, thankfully, evolved an extraordinary capacity to resolve and avoid such conflicts, offering a way to escape cycles of food scarcity, territorial violence and zero-sum competition among neighbouring groups.”
The team have observed the chimps for more than 30 years, but about 15 years ago researchers witnessed the group embark on a bloody coup to overthrow their neighbours.
Between 1998 and 2008, members of the Ngogo chimpanzee group killed 21 others in neighbouring groups.
Experts wondered what advantage could be gained from undertaking a risky war that they might not win.
They soon started to notice that females were having more offspring, but thought that could be driven by a rise in infant mortality.
However, the data showed the opposite. Females were producing more babies and more were surviving.
Higher fertility and survival rates
They concluded that territorial expansion improved female nutrition and overall health, leading to higher fertility and survival rates among young.
“In retrospect, we knew what happened, “ said John Mitani, professor emeritus of anthropology at the University of Michigan.
“We were observing all these births and there are good theoretical and empirical reasons for thinking something like this might happen,
“What we saw were very high numbers.”
Chimps are humans’ closest relative, and shared a common ancestor around 10 million years ago. The new study suggests that the human drive to conquer territory and wipe out rivals may have been embedded millions of years ago, before homo sapiens ever existed.
Dr Wood added: “Our findings provide the first direct evidence linking coalitionary killing between groups to territorial gain and enhanced reproductive success in chimpanzees.”
The research was published in Proceedings of the National Academy of Sciences.
