Comment by jmyeet

So in industrial agriculture, monocultures are a real problem. Every banana is essentially a genetically identical Cavendish. It used to be the Gros Michel until a fungus basically killed it. The same fate awaits the Cavendish. This is true of lots of produce. We, as consumers, like identical produce. But this makes the entire species vulnerable to an enterprising fungus (or virus or bacteria) and it's arguably only a matter of time.

Could this happen if every polo horse basically ends up genetically identical? Probably not in the same way but new diseases do appear. Parvo is only 50 years old.