Here's why you find certain foods disgusting (and others don't) The scientific reason why so many of us are appalled at the idea of eating one kind of animal, while we’ll happily chew on a very similar animal.

No one was expecting to find horse meat mixed in with beef during routine government food testing in Ireland, but as the contamination (as some are calling it) is turning out to be more and more widespread, other governments and major meat distributors are scrambling to do their own tests. It turns out people have been chowing down on horse not only in the UK, but in Europe, while in South Africa, consumers have been unknowingly ingesting donkey and water buffalo. It certainly raises some interesting questions about our global industrial food chain.

Perhaps more interesting is why so many of us are appalled at the idea of eating one kind of animal, while we’ll happily chew on a very similar animal. Where does this line in the sand come from? Is there a scientific reason for our disgust?

Why, yes. Yes, there is.

Social psychologists, neuroscientists and evolutionary psychologists have been studying the mechanics and causes of disgust for years. Jonathan Haidt developed a scale for measuring individual variations in sensitivity to disgust, and Paul Bloom gives a decent overview of inborn aversions, culturally-reinforced aversions and the play between the two.

Focusing more exclusively on the topic at hand, the things we do and do not want to put in our mouths, I’ll turn to Steven Pinker, whose book, “How the Mind Works,” includes a detailed section on the evolutionary origins of our disgust.

All of us have an inborn set of rules about the things we’re wiling to touch or eat. If something disgusts us, like feces or rotting meat, then we’re not willing to eat it. If we tried to force ourselves to, our body would likely respond with gagging, the result of our unconscious mind anticipating how sick it will make us.

Likewise, if something good, like a fresh red apple, were to make contact with a disgusting material, we wouldn’t want to eat it anymore. We now understand that this is an intuitive microbiology: it’s about the invisible spread of germs that make us sick. Our ancestors evolved these rules, and they further strengthened and codified them in cultural taboos about food in the millennia since. Through natural selection, those who came up with the correct hard-wired food rules went on to survive and have more descendants, and the upshot is that modern-day humans come with these rules pre-installed in our brains.

But wait, you say. What about my two-year-old, who will put absolutely anything in her mouth? And, hey, don’t they eat haggis in Scotland, grubs in Thailand and get grossed out by beef in India? How is this disgust universal when every culture eats different things?

Ah, there’s the rub. In fact, these two questions are related. We do go through a period when we’re very young and want to put everything in our mouths. That’s because the hard-wired rules of disgust haven’t kicked in yet. This is our “learning period.” You see, humans have long been omnivores, getting their nutrients from whatever combination of species — plant, animal, whatever — was available. But eating something unfamiliar can be risky, and our ancestors knew the risks were much higher when it came to animals, whose parasites and diseases in life, and decomposing bacteria and fungi in death, were that much more likely to thrive in our own bodies.

So the general rule is that plants are okay, while animal meat (and weirder things like blood, eggs, or milk) goes on the “disgusting” list by default. Getting an animal product on our “okay to eat” list means being exposed to it in early childhood, during that “chew on anything” phase. We then grow into adults with a natural aversion to every animal product except the relatively few options our parents introduced us to. In contrast, we’re never too old to discover a new vegetable or fruit.

The vegans may be on to something when they say animal products are disgusting. It’s certainly true, at least, that every animal product is disgusting to anyone who isn’t already used to it.

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