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Paul J. Zak, Ph.D. Headshot

Gay Marriage is Natural

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Co-Written by Ken Grimes

The California Supreme Court's decision to allow same-sex marriage was greeted with both joy, and indifference. Joy from the gay community, where some couples had waited over quarter of a century to officially affirm their bonds. And indifference from much of the rest of California, including the anti-gay-marriage lobby.

But, is there any science that can help shed light on gay marriage? We are wary that past scientific 'contributions' have added at least as much heat as light to the debate. Now, lets provide new insights into the brain mechanisms that support same-sex relationships.

Much of the anti-gay-marriage argument rests on two commonly held assumptions: Life-long exclusive mate-bonding for purposes of rearing joint offspring is natural, and homosexuality is unnatural.

Both assumptions have little basis in fact.

Homosexual acts have, in fact, now been widely documented across a range of mammal species (that's right -- we're 'outing' mammals!), including our closest relatives, apes and monkeys.

Research published this week in the journal Public Library of Science ONE showed that one reason that male homosexuality has survived (even though gay men produce fewer offspring than straight men) that the 'gay gene' must be somehow beneficial to women, or it would have been eliminated from the gene pool.

Meanwhile, there seems to be nothing particularly 'natural' about marriage. Only about 3% of mammal species are monogamous -- meaning they cohabitate -- and few of these species mate for life. And nearly each partner in these 'animal marriages' engage in extra-pair mating. Lifelong sexual loyalty in nature is, it turns out, a vanishingly rare commodity.

It turns out that both marriage and homosexuality are, in fact, both common for our species. As research at Center for Neuroeconomics Studies in California has shown, human attachment behaviors depend on the same 'bonding' molecule called oxytocin, also found in other mammals. When the human brain releases oxytocin, we immediately begin to care about those around us: family, friends, and even complete strangers. This effect is so unfocused, that we also care about nonhumans, too, including dogs, cats or stranded whales. We name our cars, and cry when we sell our houses.

Oxytocin is also the basis for virtuous behaviors towards strangers. Researchers in my lab have shown that in humans, oxytocin promotes trustworthiness, generosity, and empathy. These virtues make the free societies we live in possible -- without oxytocin we would need Big Brother monitoring every human interaction to eliminate crime, cruelty, and selfishness.

Because the oxytocin attachment system is a blunt instrument, it is not surprising that we see long-term same-sex partners. Our highly evolved, inherently flexible, human attachment system allows us to have a morality -- a love beyond the self -- that far exceeds anything found in our mammal relatives. So, long-term attachment between genders and within a gender should be viewed as natural as the care and affection we quite easily show to those around us.

Paul J. Zak is Director of the Center for Neuroeconomics Studies at Claremont Graduate University in Claremont, CA. His new book is
Moral Markets: The Critical Role of Values in the Economy, published by Princeton University Press. Ken Grimes is a writer based in London, UK.

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