If only our ancestors had not domesticated animals as pets, we would be doing this kind of work now...http://www.youtube.com/watch_popup?v=FZ-bJFVJ2P0 (It's a happy story of how Damian Aspinall reunites with a gorilla he raised.)
Aeons ago, our ancestors domesticated animals as their companions and made a covenant with them - Come and be our companions, we'll look after you for life. The animals agreed and all was well....for a while.
Then, our later ancestors destroyed the earth by building concrete jungles, and some of them discarded these animals when they no longer wanted them as companions anymore as the animals kept breeding uncontrollably and our ancestors could not cope with it.
The animals kept their part of the covenant and remained loyal, but the humans did not.
And so, we pick up the pieces left by our ancestors and we have to look after the strays who live amongst us now.
Else, we'll be looking after gorillas....wouldn't that be fun?