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It’s Not Just Penguins…

July 15, 2009

ResearchBlogging.org

Just like Brangelina, gay penguins always make the headlines. Years ago, Roy and Silo—two male chinstrap penguins at the Central Park Zoo—tried to incubate a rock. It never hatched. Zookeepers then gave the pair an abandoned egg, which they successfully incubated and raised to be a healthy chick.

In 2008, a wily pair of penguins at China’s Polarland Park repeatedly stole eggs from heterosexual couples and replaced them with rocks. Eventually, zookeepers gave the same-sex duo their own eggs to raise.

This spring, when a heterosexual pair of Humboldt penguins at a German zoo rejected their unhatched egg, zookeepers gave the egg to a same-sex couple of the same species. The two dads, Z and Vielpunkt, incubated the egg for about a month and are now caring for the chick as any heterosexual penguin duo would.

Of course, penguins aren’t the only animals that form same-sex couples. In a 2006 article in SEEDMAGAZINE, Jonah Lehrer wrote, “At last count, over 450 different vertebrate species could be beheaded in Saudi Arabia.”

Who? What? Where?

A recent review (Bailey and Zuk, 2009) sets out to answer those answers—or, more accurately: what non-human animals engage in same-sex sexual behavior, what are the evolutionary origins of this behavior and what are the evolutionary consequences of the behavior?

Bottlenose dolphins, Japanese Macaques, bonobos and Acorn woodpeckers may use same-sex sexual behavior to form social bonds, ease tensions and make up after a fight… Garter snakes and Goodeid fish may use male-male courtship for protection… Fruit flies may use same-sex sexual behavior as practice for heterosexual sexual behavior… Male flour beetles may use same-sex copulation as a means to indirectly inseminate a female.

For Laysan albatross, female-female pairing may maximize the reproductive success of the population. In one Laysan albatross colony in Hawaii, 31% of all pairs in the colony were pair-bonded females. (Scientists speculate that the skewed sex ratio—59% of the birds in this population were female—caused the high number of same-sex pairs.) It’s an unusual situation, but it seems to be working. The female pairs enjoy a high level of reproductive success—as parents, they’re way more successful than single females and almost as successful as male-female pairs. Scientists theorize that the pair-bonded females enable the males to have successful extra-pair copulations. In other words, males paired with one female can go off and have a fling with a female who is pair-bonded with another female and, since the two moms are very successful parents, the chances of the cheating male’s offspring surviving are quite high.

For other animals, same-sex coupling may not be much of a reproductive strategy or an adaptive response. It’s just genetic. Researchers have found that male fruit flies with mutations in specific genes (fruitless, dissatisfaction, prospero, quick-to-court, transformer, raised, genderblind or white) court other males.

In nature, same-sex behavior is not only prevalent it’s advantageous. Now really, how can people say that same-sex pairing in humans is unnatural?

Nathan W. Bailey, & Marlene Zuk (2009). Same-sex sexual behavior and evolution Trends in Ecology and Evolution

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