Genetic Sex Change: Gender Bending Animals

If you’re like me, you’re a human being with naturally defined, unchanging genitalia. I mean, chromosomal sex-determination, am I right, folks?

But if you’re not like me, you might just be one of the three animals I’m about to list. Of all the animal kingdom’s bizarre, outlandish mechanisms, midlife sex change has got to be one of the most interesting.


Let me walk you through a scenario. You’re new at school, an all-boys academy except for one girl, Jessica. Jessica spends most her time with Brad, who is of course the most popular guy in school because, I mean, his name is “Brad.” And Brad is your classic alpha male. He chugs whey protein with egg yolks and high fives with the magnitude of a Ricther-3.0 earthquake and just invented a new genre of music called Lacrosse-Rock. Brad also has a best friend, Tim, that guy who’s a little less popular but sort of absorbs some of Brad’s coolness by standing around him a bunch.

Tragically, Jessica is eaten by a tiger shark. So now there are no girls at the school, right? Wrong! As the most dominant male, Brad naturally becomes the female. And who does he take as his new primary lover but his old second-in-command, Tim.

I just described to you what must be the especially awkward high school years of the clown fish. Clown fish live in a hierarchy with the reproducing female at the top. When that female dies, her partner becomes the new female, who then selects a mate from among the other males.


Why does this happen? Essentially, scientists say, because clown fish are lazy. They basically never leave their home sea anemone. Instead of going out, looking for new partners, a group of males can just wait long enough and one of them will swap genders. Which is all well and good, except now I can’t help but feel a little nervous every time my roommates and I stay home and play Mario Kart on a Saturday night.

Califoria Sheephead

California sheephead are a kind of fish native to the Pacific Ocean. What makes them interesting is that they are all born female. But that does not mean they won’t be able to reproduce, as anyone who has seen Jurassic Park will tell you. (They will also tell, at any given time, that we are only five years away from resurrecting a Brachiosaurus using DNA preserved in mosquitoes. As a rule, do not cite “person who has seen Jurassic Park” as a credible scientific source.)


At any rate, sheephead are born female, but most of them don’t stay that way. While it’s not clear exactly which environmental cues trigger the switch, research shows it usually happens about 2/3 of the way through the sheephead’s lifespan. That means the average sheephead couple must consist of a young, bubbly female and an older, kind of creepy and probably rich male, making them just like every other couple in Los Angeles.

Unfortunately, overfishing is taking a lot of the bigger males out of the picture. To compensate, females are turning into males sooner, at smaller sizes. Which means the remaining females are generally smaller and, as a result, are laying fewer eggs. So sheephead are dying out, and you should feel terrible. If you have any ounce of decency, you’ll go dive into the Pacific and save one right now.


Not going to happen, huh? Well, leave it to a human not to understand the complexities of maintaining sex-balance in a gender-bending society. Which leads me to my final creature…


Wait, what? This is going to need its own post. Check back later to figure out what the hell I’m talking about!


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