Chimpanzee co-operation linked to 'social bond' hormone
By Michelle Warwicker
Wild chimps that had taken part in a grooming session with a "bond partner" had higher levels of the hormone in their urine than after grooming with a "non-bond partner", irrespective of whether the individuals were related.
Results of the study are published in the journal Proceedings of the Royal Society B.
Scientists tested the urine of wild chimpanzees (Pan troglodytes) in Uganda to measure the animals' oxytocin levels after grooming sessions.
Oxytocin is associated with forming mother-baby and pair
bonds, "but it's not really been implicated in non-kin relationships
before - in non-sexual contexts," said research team member Catherine
Crockford from the Max Planck Institute for Evolutionary Anthropology in
Leipzig, Germany.The non-kin relationships that exist in the animal kingdom are "almost like friendships", according to Dr Crockford.
Animals that maintain co-operative relationships have greater longevity and increased rates of offspring survival.
But relatively little is known about the processes behind non-kin chimpanzee relationships.
Comparing such social bonds to those found in humans, Dr Crockford explained: "Even though people are not related to each other and they're not in a sexual relationship where they could produce offspring, they still co-operate.
"And nobody really has a good explanation for how this can happen."
Findings of the study suggest a direct link between social bonds and co-operative behaviour.
Co-operative behaviour observed in chimps includes food sharing, collaborative hunting and grooming.
Dr Catherine Crockford, Max Planck Institute for Evolutionary Anthropology"Although chimps are perceived as being male-bonded, other bonds are clearly important too"
Grooming events can occur
between non-bond partners, but in these cases increased oxytocin levels
were not recorded, which surprised Dr Crockford.
"Until now... it's pretty much been thought that tactile
stimulation [for example] gentle stroking is enough to stimulate
oxytocin."But this clearly shows that's not the case, that you need more than just that. There needs to be some sort of psychological component really, this added factor of the relationship itself and the quality of the relationship."
The study also found that social bonds between female-female pairs and male-male pairs are both important in chimpanzee society.
This finding contrasts with perceptions that the animals tend to be "male-bonded".
"Although chimps are perceived as being male-bonded, other bonds are clearly important too," commented Dr Crockford.
The study supports the theory that enduring co-operative relationships are not purely cognitive.
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