Elayna Rico

What I can't seem to understand is why the Gorilla's and Ape's are able to verbally speak, while the horses aren't able to. Another thing to add to the horses how did they just spawn there, like they obviously don't thrive in rainforests. So its very miss leading and leads go many questions. Also if they wanted more Apes to be put in labor then why did they kill a ton of them huh?