Because the bible says so. And, it has always been the taboo in biology where biologists are a tad more reverent to religions than in other science. Bibles say

Because the bible says so. And, it has always been the taboo in biology where biologists are a tad more reverent to religions than in other science. Bibles says so: else eating/using animals would be a sin, and a lot of human «non virtuous behaviour» could be acceptable and animalism would be almost acceptable. If human beings where animals (and animals considered conscious) monotheism most important axiom would disappear and most of our social order.