If we were living with humans of other species less gifted than our own, such as neanderthals or some kind of homo hablilis, we would respect our differences and not regard them as creatures to be used to serve us. The fact that the closest species to us on the evolutionary scale are chimpanzees, however, puts us in a more delicate position: how much to they suffer, are they masters of their destinies and do they have some characteristics we would attribute only to man? On the other hand, the intelligence of some people with pschiatric disabilities is not far removed from superior primates. Should we respect the former as humans and not the latter? Is species the line of separation? This book attempts to deal with ethical issues by examining the biology of animals, broaching concrete problems of our times.