Because the skin is not the only point that can give information of something going wrong?

Yes, but when you're a caveman or peasant, there's not much you can do about physical trauma to your internal organs. External pain is useful because you can usually take action to stop it.

(Obviously with the advent of modern medicine, internal pain is useful.)

>Yes, but when you're a caveman or peasant, there's not much you can do about physical trauma to your internal organs.

For one, you can sit still until they heal, and avoid straining them further.

Second, internal pain after eating something bad (e.g rotten or poisonous) for example, helps you avoid eating it again.

Just off the top of my head -- I'm pretty sure there are tons of other cases.

Hm, OK. I'll buy this. I forgot that "doing nothing" is actually something you can do.