But then, analogues to heterosexual marriage are imperfect in animals, too. Long-term pairing is rare, particularly among mammals; our only close relatives to exhibit it are gibbons, those long-armed apes that whoop like banshees across Asian rain forests. And as far as monogamy goes, we are not as devoted as many species, since partner changes and infidelity are common.
It is noteworthy that Roy and Silo belong to a species in which offspring are always raised by two parents. A similar male duo would be extremely unlikely in, say, peacocks, because male and female peacocks never stay together under the best of circumstances. Roy and Silo are still behaving like penguins in many respects, but if every penguin did exactly what they are doing, we would soon be sadly short of penguins. What that doesn't mean is that no penguin should do it, or that doing it is somehow unnatural or wrong.
President Bush declared that "marriage cannot be severed from its cultural, religious and natural roots," but those natural roots leave humans huddled in a defensive little group of monogamists that includes gibbons, snow geese, marmosets, a couple of kinds of cockroaches, and of course those two penguins, gazing out at the hugely nonmonogamous rest of the natural crowd.
This hardly suggests that we resign ourselves to the breakdown of marriage as an institution, however. As virtually everyone examining animal homosexuality has pointed out, whether or not animals exhibit a behavior is not grounds for emulating it. Marriage itself is a social and legal invention, not a literal translation of other species' actions. Roy and Silo can't get married, but neither could a male and female penguin. Neither gay nor straight marriage is particularly natural, if by natural you mean that it is found among a wide range of animals or rooted far in our evolutionary past. This should not bother us any more than it should bother us that we are the only species with flush toilets. At the same time, we should not view marriage as a cultural weapon necessary to keep our "animal instincts" toward sex with anyone, anytime, at bay. Animals -- and people -- do a lot of different things, and forming long-term pair bonds is one of them.
