Duck dongs

Which came first, the phallus or the complicated lower oviduct?

Published May 4, 2007 6:35PM (EDT)

This article came out a couple of days ago, but I feel I would be irresponsible to not call attention to this gem from the New York Times about a previously misunderstood weapon in the evolutionary war of avian genitalia: the duck phallus.

For anyone who missed it, here's a summary: Most male birds don't have phalluses. They just have holes from which they release sperm. But the duck is not just any bird. Not only do the males have phalluses to begin with, but their phalluses are so large that they can grow to be the length of their bodies. What's more, come fall, their phalluses disappear, only to be regrown the following spring.

Let's first give collective thanks to Mother Nature for not endowing human males with duck phalluses. Second, check this out: A behavioral ecologist named Patricia Brennan has just published a paper in PLoS ONE asserting that the reason male ducks' phalluses are so extreme is that they're in a genital arms race -- not with each other, as was previously assumed, but with female ducks.

Apparently it hadn't occurred to anyone that the guys might be reacting to the girls -- but to Brennan, it made perfect sense. In one of my favorite quotes of the article, she points out, "Obviously you can't have something like that without some place to put it in. You need a garage to park the car."

True enough. And it turns out, that garage is pretty strange -- ducks' lower oviducts (i.e., the duck equivalent of a vagina) have "all these weird structures, pockets and spirals," says Brennan. She hypothesizes that the female ducks' complicated oviducts are a defense mechanism: If a female is forced to mate with an unwanted male, she can capture his sperm in one of her oviduct's pockets and expel it later. Also, having a long, complicated oviduct means that potential mates will need to have long and complicated phalluses if they want a good chance at reproductive success. In other words, male ducks might have evolved elaborate phalluses to keep up with the females' ever lengthening oviducts. (My question: Where does the race end? Surely there comes a point where your oviduct starts to get in the way of other organs?) And Brennan has statistics to back up her hypotheses -- she estimates that a third of all duck matings are forced, but only 3 percent of duck offspring are from forced matings.

Crazy, right? But the other crazy thing is that no one before Brennan thought that the female ducks might have anything to do with the males' crazy genitals -- a point made by one of her co-researchers, Kevin McCracken, and summarized thus:

"Dr. McCracken, who discovered the longest known bird phallus on an Argentine duck in 2001, is struck by the fact that it was a woman who discovered the complexity of female birds. 'Maybe it's the male bias we all have,' he said. 'It's just been out there, waiting to be discovered.'"

By Catherine Price

Catherine Price is an award-winning journalist and author of Vitamania: How Vitamins Revolutionized the Way We Think About Food. Her written and multimedia work has appeared in publications including The Best American Science Writing, The New York Times, Popular Science, O: The Oprah Magazine, the Los Angeles Times, The San Francisco Chronicle, The Washington Post Magazine, Salon, Slate, Men’s Journal, Mother Jones, PARADE, Health Magazine, and Outside. Price lives in Philadelphia.

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