Here's a thought experiment: Imagine that I breed gorillas. Soon after reaching adulthood each gorilla is killed and made into dog food. One day I discover a gorilla whose mental abilities are similar to a 6-year old human child. That is, the gorilla can reason, communicate, be creative and show empathy just like a child. Is it OK to kill that gorilla? If so, how about an '8-year-old child' gorilla? Or 10-year-old?