If today's human lived alongside other less endowed human species than ours (some sort of Neanderthal or Homo habilis) we would respect their differences and not consider them beings that we can use for our service. However, the fact that the closest species on the evolutionary scale to us, is the chimpanzee, puts us in a more delicate situation: to what extent do they suffer, are they masters of their fates or do they enjoy some features that we attribute only to man? Moreover, some mentally handicapped have intelligence not unlike some higher primates. Should we respect some as humans and not others? Should the line that separates us be determined by species? Why establish divisions between species and not within them? This book aims to address ethical concerns from an animal biology perspective, addressing specific real-world situations.