"We" claim that we have the right to use animals because they are different than us, just as white men used skin color as a justification for slavery. However, from a genetic perspective the gaps in genes between us and our closest animal relative is arbitrary. We just happen to be the lucky survivors in the evolutionary race. As a thought experiment, it's perfectly acceptable to imagine a world where all the genetic "gap species" were still alive. Thus, between us and the bonobo there would be a continuum of living beings, all almost identical to their genetic neighbor. In such a world, it would be impossible to draw a line between us and the bonobo where we could say "From hereon oppression begins", and justify it with any kind of argument. The primates on either side of the oppression line would be identical except for one gene. The differences in appearance, intelligence and senses (if such a word exists) would be so small that no test except a careful DNA test could tell them apart, and I'm not sure even DNA tests are accurate enough. Thus, they would be identical to each other, yet one of them would be doomed to be oppressed while the other would benefit from our protection. Since this would be a totally unacceptable and morally indefensible stance, we'd have no choice but to grant the bonobos the same rights as humans, to not be used as property. Of course, the though experiment is easily expanded to include ALL living beings since we share a common ancestor. - Richard Dawkins