Nemo the Sex-Changing Clown Fish: The presence of sex alteration in the animal kingdom.

In the sheltered reefs of the Pacific Ocean, a strange but fascinating phenomenon is about to take place. The largest male clown fish in the school has spent the day asserting his dominance in an effort to remain on top. It’s tiring work, as he must defend his throne from any of the subordinate males that may want a taste of his power. To prevent this from happening, he must hoard all the resources he can and monitor their food intake, just so they can’t grow bigger and stronger than him. But all of this hard work is worth it, because at the end of the day, he alone has the privilege of mating with the schools only female. His anemone is clean and inviting, and he’s ready for the magic to happen.

But where is she? He’s been waiting all evening but she has not arrived at his anemone like she was supposed to. Surely she hasn’t stood him up. She too knows how important this arrangement is, with procreation and the spreading of her genes being her sole purpose in life. So he continues to wait. And wait. Little does he know, she’s never going to turn up. Unfortunately for him, his sole chance at mating has just been eaten by a shark.




So what’s a guy to do? He can’t sit around and wait forever. The drive to mate is strong and who knows, maybe tomorrow he too will be eaten by a shark? He’s got to mate, and he’s got to mate now. Where’s he going to find another female? There was only one in his school, and she’s gone now, so he’s only left with other men. There’s only one solution.


He’ll have to turn into a female.


Clown fish exhibit a phenomenon known as sequential hermaphroditismwhich is the ability to change sex at any point in their life. All clown fish are born male with active male reproductive organs, but also dormant female reproductive organs. If a dominant male clown fish finds himself in a situation where the dominant female dies, he will quickly transform himself into the new dominant female. A struggle for the position as new dominant male will then ensue amongst the subordinate males, and the successor will mate with the new female. It’s a win-win for the original dominant male. Yes, he had to undergo the energy consuming process of changing sex, but he still gets to pass on his genes. Success!

As crazy as this process may sound, it turns out that it isn’t all that uncommon in the ocean. Other species that exhibit sequential hermaphroditism include moray eels, wrasses, parrot fish, and gobies. Cuttlefish are not able to anatomically change their sex, but are able to change their colouring to appear as a different sex. This trick comes in useful to male cuttlefish during the mating season, as it allows the male to move in between a flirting male and female, and split his appearance down the middle so that the female sees him in his true male form, while the other male is fooled into believing that he has attracted over another female. Little does this naive male know, but his mate has just been hijacked by the cunning impostor.

Up on dry land, another species that can change sex is the chicken. When born, female chickens have two different sex organs, but the presence of female hormones causes the left ovary to develop while the right gonad lays dormant. In some cases a medical condition may cause the ovary to shut down and the right gonad to develop, causing the female to develop a somewhat male appearance. It has also been found that stored chicken feed can produce mycotoxins which act like synthetic hormones when consumed, resulting in some startled farmers waking up to fields of rooster look-alikes.


So how about us humans? 


Although the process of changing sex in humans is not as straightforward as in clownfish, there are many people who do it. From performance cross-dressing in ancient Greek theatre to the drag queen shows of today, humans have a long history of dressing up as the opposite sex. But actually changing sex fully is a more complicated process. These days many people who identify as transgender can undergo reassignment surgery so they can anatomically match their gender identity. It’s estimated that 0.6 percent of the adult population in the US identify as transgender – that’s 1.4 million people! Certain intersex conditions can also lead to a natural sex change in people, with most of these cases following the pattern of females developing male characteristics as a result of high testosterone production during puberty. It is believed that one in every 150 people have some form of condition that would classify them as intersex.


Prevalence of intersex conditions within the population


So as it seems, mismatched gender identity and intersex conditions are relatively common in humans. But looking at it from an evolutionary point of view, it doesn’t really make sense why it would be so prevalent. If we break it down and look at our lives in a biological sense, isn’t our main goal in life to have lots of babies running around, carrying our genes?

Well, it turns out that isn’t the case. Transgender people were actually seen as an asset in several early human societies, and helped in the evolution of our species. Among hunter-gatherer societies transgender men were considered useful to their communities as extra help around the house, helping to raise children, gather and prepare food, and maintain the household. The societies that accepted and valued these transgender men had an evolutionary advantage, allowing them to remain healthy and survive. Researchers also believe that these benefits allowed transgender attributes to continue through generations and into today, even though the transgender individuals had no children of their own.


With these evolutionary findings comes a message that we should keep in mind today. In order for these transgender individuals to contribute fully to society, they had to be accepted by its members. Ultimately, the more accepting communities benefited and gained a survival advantage.

With over a million transgender people in the US alone, wouldn’t it be in our interest to support them and fully accept them for who they are?




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