The more I learn about horses the more they seem like a creature that’s continually trying to die - and humans get to try and stop them succeeding.

Perhaps that's how aliens would see humans. Perpetually trying to die except for a small group of humans fighting disease, monitoring and protecting climate, keeping order, etc.

Horses are especially susceptible to *everything*.

Millenia of selective breeding to try for the healthiest strongest animals we can, and they're still shit.

They'll get ill if they breathe wrong. They'll get ill if they eat a mouthful too much or too little of grass that's ever so slightly too green. They'll get ill if it's too rainy or not rainy enough.

How the hell did they even evolve?

Selective breeding for being useful to humans, not for being able to survive on their own.

The two are not in any sense mutually exclusive.

Sure, there is some overlap. But there are also certain traits that would mean instant elimination from the gene pool in the wild but don't matter much when a human takes care of the horse.

I'm sure that if you investigate feral horse populations like North American mustangs or Australian brambies, you will find out that they don't "get ill if they breathe wrong". Because all that did, died without leaving any offspring long time ago.

> But there are also certain traits that would mean instant elimination from the gene pool in the wild but don't matter much when a human takes care of the horse.

Yeah. They had that in the wild too.

> you will find out that they don't "get ill if they breathe wrong"

They very much do. If anything they're worse than domesticated horses.