[pbhjpbhj]

Having an repulsion for shit is a healthy adaptation. But it seems that for some people they're much more sensitive.

Similarly, it's probably useful for a primitive person to vomit on sight of a familiar person vomiting, collective protection. Definitely a trait to find out before going to space!

[mikkupikku]

The one I've never got is how so many people faint or become I'll when they see blood. Always seemed like a massive maladaptive that should create even more risk in a presumably dangerous situation. If a tiger attacks me in the night and the guy next to me faints because I'm getting eaten, we'll both end up dying.

[the_af]

It seems maladaptive. I faint (sometimes) at the sight of my own blood, and must look away when nurses draw it. I also get queasy when even talking about blood or reading about it. I can't think of any good reason this would be helpful; in fact keeping my cool would be advantageous.

And yes, I do have a very vivid imagination.

[asdff]

Rival tribe comes and kills Lug and Glug. You faint at seeing the bloodshed. They assume you died. They leave. You live and pass on your fainting genes.

Alternatively it could just be an overshoot of the behavior to recognize that you bleeding is a dangerous situation. These behaviors probably follow some gaussian distribution in their potential "effect" among the population and fainters are on a long tail of that distribution.