Crass, sure, but true. Humanity is the reason certain animals are even capable of continuing existing. For example, chickens, pigs, cows, etc. The populations (

Crass, sure, but true. Humanity is the reason certain animals are even capable of continuing existing. For example, chickens, pigs, cows, etc. The populations (and genetic diversity) would be far less if they were allowed to roam naturally all the time. With farmers releasing cows to free range, as well as keeping and breeding cows, the cow as a species is guaranteed to survive. It's a complicated subject but the simplest answer goes back to the circle of life. There are two survival strategies of a species. Either becoming a predator, or become very useful prey. Which, in crass terms, basically means that if humans don't buy it (don't eat it, therefore don't insure it's survival), it will die out (e.g. it's "worthless") if it cannot evolve into a predator species.