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hormones, s*x, & fidelity...

At Scicon, Bernard Beckett talked about getting people excited about science by telling stories about cool science stuff. One of his examples was how he told one of his classes about what makes voles monogamous or promisuous. Racy stuff! I remember reading about this some years ago in a book by US author Natalie Angier, & today I thought I'd revisit it.

Voles are cute little rodents. There are many different species - and although they look superficially rather simlar, they can vary widely in their behaviour. Take prairie voles and montane voles, for example. Prairie voles are social and monogamous, living in groups but staying faithful to their mate. Montane voles, however, are promiscuous but spend their time alone when they're not out mating madly with other voles. Why the difference?

The secret lies in a couple of hormone: oxytocin, & vasopressin. Vasopressin leads male prairie voles to be monogamous - block its action, & they won't form a lasting pair bond with a female. Oxytocin plays the same role in female prarie roles. Administering these hormones to montane voles has no effect - they remain promiscuous - and yet both species have the same levels of both hormones in their blood. But again, why the difference?

The difference lies in the animals' brains - both species use the same receptor molecules for oxytocin & vasopressin, but these receptors are found in different areas of their brains. In the monogamous prairie voles, the vasopressin & oxytocin receptors are found in what's been called the 'reward region' of the brain: an area that we know also reacts to addictive drugs. When a virgin prairie vole mates with a female, the shot of vasopressin that's released into his blood hits this reward region and he effectively becomes 'addicted' to that female - a monogamous relationship is born. (Mind you, this is no 'quickie' - prairie vole matings last 12-24 hours!)

Marla Broadfoot (2002) reports on a piece of research that takes our understanding of this hormonal control of mating behaviour even further. Using a virus as a vector, scientists increased the number of vasopressin receptors in the reward region of male prairie voles' brains. The result: they formed monogamous relationships without the need for actual physical sex.

These findings have led to the inevitable question - does the same system work for humans? And could people be 'engineered' for fidelity? The answer - we don't know enough about the human brain to even begin to answer this question. So anyone suggesting that humans could be made more like prairie voles really is drawing a long bow (sorry, Cupid!)

N. Angier (1995) The beauty of the beastly. Houghton Mifflin.

M.V. Broadfoot (2002) High on fidelity. American Scientist 90 (3): 1 

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