One interesting science nugget I think we’ve all heard is the idea that certain phobias are programmed into our DNA. For example, we’re supposed to have a revulsion of snakes and spiders since they are notorious carriers of venom. Personally, I don’t have any real issues with spiders, but I can speak to an interesting experience I recently had with snakes: I was walking up a mountain near my dad’s house and came across a large rattlesnake laying out in the sun, a recent meal making a noticeable bulge in his belly. It did give me a little bit of the heebie-jeebies. I could feel a jolt run up and down my spine, and a slight turning in my stomach. It’s weird, because I think this is specific to rattlesnakes. I spent a lot of my summers as a kid in the Rocky Mountains of Montana, and I used to catch snakes all the time with no ill effects. But this was the first time I’d seen a rattlesnake.

Another likely example of a pre-programmed phobia? Our revulsion towards dead, rotting, decaying corpses. This works to our benefit because corpses often contain infectious agents — that’s why we bury or burn our dead.

Incest is another example of something we seem to have an innate revulsion for. Consider the following thought experiment:

Julie and Mark are brother and sister. They are traveling together in France on summer vacation from college. One night they are staying alone in a cabin near the beach. They decide that it would be interesting and fun if they tried making love. At very least it would be a new experience for each of them. Julie was already taking birth control pills, but Mark uses a condom too, just to be safe. They both enjoy making love, but they decide not to do it again. They keep that night as a special secret, which makes them feel even closer to each other. What do you think about that, was it OK for them to make love? — A thought experiment devised by Jonathan Heidt

Some might argue that there are rational (not innate) reasons to oppose such an act. Cognitive psychologist Steven Pinker disagrees.

Most people immediately declare that these acts are wrong and then grope to justify why they are wrong. It’s not so easy. In the case of Julie and Mark, people raise the possibility of children with birth defects, but they are reminded that the couple were diligent about contraception. They suggest that the siblings will be emotionally hurt, but the story makes it clear that they weren’t. They submit that the act would offend the community, but then recall that it was kept a secret. Eventually many people admit, “I don’t know, I can’t explain it, I just know it’s wrong.” — Steven Pinker

“I can’t explain it,” would seem to be an indicator of some innate revulsion, either built into our DNA, or planted early in our conscious existence.

I’ve long thought the same might be true for homophobia. Certainly, from the point of view of a species looking to continue its existence, homosexuality would be a detriment. It might not be a problem if homosexuals are a small percentage of the species population, but, obviously, the more homosexuals a species has, the less likely its odds of long-term survival. (There are a number of interesting, theoretical caveats to this statement, but I think the gist of it stands.) As such, it’s possible that a revulsion to homosexual acts could be built into our DNA.

Here’s the interesting thing: I find I don’t really feel these revulsions (aside from the rattlesnake thing.) Rotting, decaying corpses? Boring. The incestuous relationship described in the experiment above? Doesn’t really bug me. General homosexual behavior? Eh.

Here’s an interesting thought experiment to test your own level of revulsion. Imagine you are performing oral sex on a person of your gender. I mean really imagine this — contemplate the groans the person is making, the taste and texture of their sex in or around your mouth. Then, look up at them and realize that they are a long dead, rotting zombie. And as you watch, hundreds of snakes and spiders crawl out of their eye and nose holes.

You can let me know your results in the comments.