"Thanks to medical science, surgery and hygeine, we have reached an incredible peak of breeding success. We have practised death control and now we must balance it with birth control. It looks very much as though, during the next century or so, we are going to have to change our sexual ways at last. But if we do, it will not be because they failed, but because they succeeded too well...
We already know that if our populations go on increasing at their present terrifying rate, uncontrollable aggressiveness will become dramatically increased. This has been proved conclusively with laboratory experiments. Gross over-crowding will produce social stress and tensions that will shatter our community organizations long before it starves us to death... If a selective attempt is made to stem the breeding flood, with certain pairs permitted to breed freely and others prevented from doing so, then this will work against the essential cooperativeness of society--the pair-bonding pattern will suffer.
To sum up then, the best solution for ensuring world peace is the widespread promotion of contraception or abortion. Abortion is a drastic measure and can involve serious emotional disturbance... Contraception is obviously preferable, and and religious or other 'moralizing' factions that oppose it must face the fact that they are engaged in dangerous war-mongering."
-Desmond Morris, 1967 in The Naked Ape