Loved-up lemurs shed (some) light on the mystery of monogamy ©David Haring, Duke Lemur Centre

Loved-up lemurs shed (some) light on the mystery of monogamy

'Cuddle chemicals' oxytocin and vasopressin seem to influence different species’ tendencies to settle down or play the field.

We humans are pretty obsessed with finding ‘the one’ – that special person that we can settle down and grow old with. But many species in the animal kingdom have a different idea about relationships.

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While around 90 per cent of bird species practice some form of fidelity to a single partner, just 3 per cent to 5 per cent of mammals do.

But what exactly is it that makes some animals form lifelong bonds while others are content to play the field?

According to a study carried out by a team at Duke University involving a group of lemurs, distant primate cousins of humans hailing from the island of Madagascar, it seems that brain circuitry may be the key to making love last in some species and not in others.

Studies carried out over the last 30 years in rodents suggest that the action of two hormones on the brain released during mating, the so called ‘cuddle chemicals’ oxytocin and vasopressin, play a large part in establishing long-term pair bonding.

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For example, when comparing the brains of monogamous prairie voles with their promiscuous counterparts, montane voles and meadow voles, researchers found that prairie voles had more docking sites for these hormones, particularly in parts of the brain’s reward system.

In the new study, the researchers used a specialist brain imaging technique to map the binding sites of oxytocin and vasopressin in the brains of 12 lemurs that had died of natural causes.

They found that oxytocin and vasopressin appear to act on different parts of the brain in lemurs compared to previous studies on rodents, suggesting that the picture is more complex than originally thought.

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“There are probably a number of different ways through which monogamy is instantiated within the brain, and it depends on what animals we’re looking at,” said lead author Dr Nicholas Grebe, a postdoctoral associate at Duke University. “There’s more going on than we originally thought.”

Reader Q&A: How did the heart become synonymous with love?

Asked by: Sandra Meyer, Exeter

The Ancient Egyptians noticed that the veins and arteries, as well as many nerves, radiate outwards from the heart, and concluded that it was central to both reason and emotion. Later, the Ancient Greeks moved responsibility for rational thought to the brain, but passion has always remained associated with the heart.

The adrenaline surge from any strong emotion has a powerful effect on our heart rate, so naturally we feel the pangs of love and attraction in our chest first.

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