Answer on @Quora by @AdrianaHeguy to In terms of biological evolution, why do humans squirm – Xochielt Sanchez
Answer by Adriana Heguy:
There are two factors here, and they are not necessarily interrelated:
1. The killing itself. We can't avoid to feel bad at the thought of killing or hurting an animal because we feel empathy. Empathy is part of our biology; other mammals have this too; they react badly to other animals being hurt or suffering, and not just primates, rats too. Empathic favor is selected for, in social species, because without empathy within the group, there would be no cohesion and no bond, and the group would not be successful. Social animals need to be able to get along.
I highly recommend this book:
Humans are extremely social animals, and we are empathetic by nature (though empathy can of course be suppressed and discouraged by society or different behavioral manipulations such as desensitization, dehumanization, etc.). We understand that being killed or hurt does not feel good, and we feel sorry for the animal. Of course, if we need to kill to survive, we will do it. But we still feel bad for the animal, even if you kill it. Many cultures thank the animal for its sacrifice, after hunting it. We understand that taking a life is not something to be done lightly, even if it's not a human life. Buying meat from the supermarket has dissociated the killing from the eating, and that has allowed increased consumption without giving the animal, or the environment, a second thought.
2. The contact with animal organs and blood. The sense of disgust many people feel about chopping an animal to pieces, gutting it, or skinning it, is likely to arise as a way of protection against viruses and bacteria, harmful pathogens that can come from animals. It's probably rooted in behaviors also favored by evolution, collectively known as disease avoidance. Check out this New York Times article:
And also Paul Rozin's research into the nature of disgust: