Unicorns have appeared in the myths and legends of numerous ancient cultures. Nowadays they are a universally recognized creature that has become synonymous with rarity. So it seems strange that despite being so widespread, and ultimately being such a simple concept, that unicorns don’t exist. After all, it’s just a horse with a horn. But in reality, the rules of evolution and development forbid unicorns from existing.
The first issue is a very simple matter of natural selection. Horses typically eat by grazing, and an animal that needs to frequently lower its head to the ground would certainly be inconvenienced by a giant spike on its forehead. The horn would be getting stuck in the ground all the time. Usually ornamental features like this don’t provide much of an advantage except in rare instances for attracting mates, and traits whose costs outweigh their benefits typically aren’t favored by evolution. There are not many circumstances where a horn would be beneficial to a horse’s lifestyle, so such an adaptation like this wouldn’t stick around.
But even if natural selection failed, there are still physical, developmental constraints preventing horses from growing horns. The next rule that unicorns break is the developmental rule of bilateral symmetry. Almost every animal develops their body in such a way that it is perfectly symmetrical along one axis. Sometimes there are exceptions to this where a structure is built on only one side, like the way certain snails’ shells coil or the human heart favoring the left side of the body, but there are never any circumstances where a structure is built directly on the midline, like a unicorn’s horn. At this point many people are probably trying to think of exceptions. One that often comes to mind with unicorns is the narwhal. They are commonly referred to as “the unicorns of the sea.” But narwhal “horns” aren’t horns at all, and are in fact a modified tooth protruding from one side of the face, which is much more apparent looking at a narwhal’s skull. This approach of elongating a tooth probably wouldn’t look as elegant on a horse.
The nose is another structure that seems to be an exception at first glance. Just looking in a mirror, you can tell that it’s directly in the middle of the face. In reality, though, the nose is actually the result of two symmetrical structures on either side of the face coming together and fusing on the midline. This method works for the nose because of the way bones are situated around the front of the face, but the same concept couldn’t be transferred up to the forehead.
So clearly unicorns aren’t meant to exist in nature. But what about mad science? Could we artificially create a unicorn? Maybe. There’s a chemical called bone morphogenic protein, or BMP, that causes bones to develop in embryos. Studies show that applying this protein can cause bone to form in places where it otherwise wouldn’t. So maybe we could use BMP to make a unicorn horn. But this is a bad idea for a few reasons.
First of all, ethics. I think it goes without saying that this would be horribly inhumane and the animal would probably not enjoy it.
But second of all, and this one might be controversial, unicorns aren’t special. I think that the idea of using a unicorn as the poster child for uniqueness is an absolute injustice. The concept of a horse with a horn is so unbelievably boring and uninspired, especially when there are so many other better options in real life. In contrast, take a horse, put it on stilts, quadruple the length of its neck, attach some pom-poms to its head, and just for fun, paint it with polka dots. What I just described is absolutely insane. If I said any of that out of context you’d think I was a madman, but this thing exists! It’s just a giraffe. And honestly, I tried my best to make my version look bizarre, but the real giraffe is still far stranger. Yet if I showed you a picture of a giraffe right from the beginning, you probably wouldn’t have thought twice about it. My big point here is that when we go searching for unicorns, we end up ignoring the truly remarkable monsters that already live in our world.
Monster Biology 