"As a zoologist I cannot discuss sexual ‘peculiarities’ in the usual moralistic way. I can only apply anything like a biological morality in terms of population success and failure. If certain sexual patterns interfere with reproductive success, then they can genuinely be referred to as biologically unsound. Such groups as monks, nuns, long-term spinsters and bachelors and permanent homosexuals are all, in a reproductive sense, aberrant. Society has bred them, but they have failed to return the compliment. Equally, however, it should be realized that an active homosexual is no more reproductively aberrant than a monk. It must also be said that no sexual practice, no matter how disgusting and obscene it may appear to the members of a particular culture, can be criticized biologically providing it does not hinder general reproductive success."

“Sexual behaviour in our species goes through three characteristic phases: pair-formation, pre-copulatory activity, and copulation, usually but not always in that order. The pair-formation stage, usually referred to as courtship, is remarkably prolonged by animal standards, frequently lasting for weeks or even months. As with many other species it is characterized by tentative, ambivalent behaviour involving conflicts between fear, aggression and sexual attraction. The nervousness and hesitancy is slowly reduced if the mutual sexual signals are strong enough.”

“The idea that it is funny to see wild animals coerced into acting like clumsy humans, or thrilling to see powerful beasts reduced to cringing cowards by a whip-cracking trainer, is primitive and medieval. It stems from the old idea that we are superior to other species and have the right to hold dominion over them.”

“A third solution is to provide and promote harmless, symbolic substitutes for war; but if these really are harmless they will inevitably only go a very small way towards resolving the real problem. It is worth remembering here that this problem, at a biological level, is one of group territorial defense and, in view of the gross overcrowding of our species, also one of group territorial expansion. No amount of boisterous international football is going to solve this.”

“All the higher forms of animal life are aware of at least some of the other species with which they share their environment. They regard them in one of five ways: as prey, symbionts, competitors, parasites, or predators. In the case of our own species, these five categories may be lumped together as the ‘economic’ approach to animals, to which may be added the scientific, aesthetic and symbolic approaches. This wide range of interests has given us an inter-specific involvement unique in the animal world.”

“I discovered long ago that, if you write a book about cats or dogs, everybody loves you, but if you dare to write a book about human beings, all hell breaks loose. It is impossible to write an uncensored, honest book about human behaviour without offending at least part of your audience. If you feel you have a basic truth to tell, then you must tell it and be prepared to suffer the inevitable criticisms.”

“Since none of these gods exist in a tangible form, why have they been invented? To find the answer to this we have to go right back to our ancestral origins. Before we evolved into co-operative hunters, we must have lived in social groups of the type seen today in other species of apes and monkeys. There, in typical cases, each group is dominated by a single male. He is the boss, the overlord, and every member of the group has to appease him or suffer the consequences. He is also most active in protecting the group from outside hazards and in settling squabbles between lesser members. The whole life of a member of such a group revolves around the dominant animal. His all-powerful role gives him a god-like status.”