Despite our grandiose ideas and our lofty self-conceits, we are still humble animals, subject to all the basic laws of animal behaviour. Long before … - Desmond Morris

Optimism is expressed by some who feel that since we have evolved a high level of intelligence and a strong inventive urge, we shall be able to twist any situation to our advantage; that we are so flexible that we can re-mould our way of life to fit any of the new demands made by our rapidly rising species-status; that when the time comes, we shall manage to cope with the over-crowding, the stress, the loss of our privacy and independence of action; that we shall re-model our behaviour patterns and live like giant ants; that we shall control our aggressive and territorial feelings, our sexual impulses and our parental tendencies; that if we have to become battery-chicken apes we can do it; that our intelligence can dominate all our basic biological urges. I submit that this is rubbish. Our raw animal nature will never permit it. Of course, we are flexible. Of course, we are behavioural opportunists, but there are severe limits to the form our opportunism can take. By stressing our biological features in this book, I have tried to show the nature of these restrictions. By recognizing them clearly and submitting to them, we shall stand a much better chance of survival. This does not imply a naive ‘return to nature’. It simply means that we should tailor our intelligent opportunist advances to our basic behavioural requirements. We must somehow improve in quality rather than in sheer quantity. If we do this, we can continue to progress technologically in a dramatic and exciting way without denying our evolutionary inheritance. If we do not, then our suppressed biological urges will build up and up until the dam bursts and the whole of our elaborate existence is swept away in the flood.

Having said all this, I must now point out that there is an important exception to the rule. The biological morality that I have outlined above ceases to apply under conditions of population over-crowding. When this occurs the rules become reversed. We know from studies of other species in experimentally over-crowded conditions that there comes a moment when the increasing population density reaches such such a pitch that it destroys the whole social structure. The animals developed diseases, they kill their young, they fight viciously and they mutilate themselves. No behaviour sequence can run through properly. Everything is fragmented. Eventually there are so many deaths that the population is cut back to a lower density and can start to breed again, but not before there has been a catastrophic upheaval. If, in such a situation, some controlled anti-reproductive device could have been introduced into the population when the first signs of over-crowding were apparent then the chaos could have been averted. Under such conditions (serious over-crowding with no signs of any easing up in the immediate future), anti-reproductive sexual patterns must obviously be considered in a new light.
Our own species is rapidly heading towards just such a situation.

At first sight, it is surprising that religion has been so successful, but its extreme potency is simply a measure of the strength of our fundamental biological tendency, inherited directly from our monkey and ape ancestors, to submit ourselves to an all-powerful, dominant member of the group.