Uh, pretty sure cotton didn't evolve to fix that for animals.

There's of course significant processing applied to those materials before they're suitable as clothing (cotton obviously needs to be picked, it's not on an animal to begin with; leather needs to be tanned).

Lots of people are allergic to wool. Perhaps as much as a quarter to a half of the population will have a mild allergic reaction if they have ordinary coarse wool rubbing against their skin for a long time, like wearing a woollen collar or scarf while trudging through the snow all day. Some people can recognise whether fabric contains wool just by touching it with their fingertips: an immediate itching sensation. So perhaps it evolved for use by sheep, not humans?

Looks like it’s closer to 6% [1]. A lot of people self-diagnose wool allergies, but they really just get crappy wool, or they mistake itchiness caused by the coarseness of the material for an allergy. It’s an easy mistake to make, but it’s unfair to call it an allergy.

[1] https://www.ncbi.nlm.nih.gov/m/pubmed/23665833/

What about merino wool? It is said to be much less of an issue with allergies, and we see it everywhere these days.

Wool makes me itchy (I still wear it just not against my skin) but cashmere and merino don't have the same effect.

> obviously

Huh? They're obviously optimized for regulating the temperature of the animal they came from. Except for cotton and linen. And they weren't woven. Viscose is pretty comfortable, but it's not a natural fiber. Fiber blends are pretty amazing, too. There's some interesting properties you can get with blends.