MonoRealism Philosophy Site

Sex, Drugs and Rock'n'Roll

Philosophical Reflections XXII

Part A

The title is just to get your attention: I don't mention drugs or rock'n'roll.

If you found that statement amusing, it illustrates how pervasive human interest in sex is. As any advertiser knows, the mention or images of sex will grab people's attention: whether interested or offended, they're seldom indifferent.

So it is not surprising that moral rules about sex – with whom, how, when, where, why – have proliferated in history. But such moral rules were not worked out by a rigorous process of rational thought. So they are a mixture of the rational and irrational, of traditions that more or less "work" under circumstances more or less current – with a bias towards what those with most power wished. This raises the question: what would a rational sexual morality comprise?

Much sexual morality appears to have sprung up from nothing better than primitive herd mindlessness (like morality in general, most people simply absorb and accept what they've been raised with, so it amounts to: "different from our tribe's traditions is bad"). But some important objective facts of reality have been prime influences. The two basic ones are that sex exists to produce children, but children are difficult and costly to raise.

The Sexual Evolution

In our evolution, those two facts, combined with the nature of human biology, have resulted in certain emotional and psychological consequences in the human psyche. An important point here is that the more sophisticated the brain, the more are evolutionarily desirable behaviours accomplished via emotional and psychological factors, rather than by instinctive behaviours and automatic responses. Pet owners can see this in what motivates their dog vs their budgie vs their goldfish. The basic emotional and psychological make-up of human beings is the result of such an evolutionary process.

Thus an investigation of our evolutionary history can give us useful clues about why human beings are the way they are. Having the power of reason, we have free will: but that doesn't mean that we are free to act in any way we can imagine. If our aim is to live and be happy, then we have to live in a way proper to men and women. That includes living in accordance with not only our physical nature but also our emotional and psychological nature.

Note, however, that while such an analysis might inform us as to why people have a certain nature, tend to seek similar values or tend to behave in certain ways, it does not necessarily imply that we must or should act that way. The criterion of the good is not the leftovers of millions of years of prehuman evolution – what worked for ape troops – but what is good for the life of a thinking being here and now. We must take into account whatever tastes, tendencies and urges we have: but evaluate their desirability by objective criteria. Here is an analogy to illustrate that point. If your personal psychology included an obsessive desire to cut yourself, objective criteria would call it an illness needing to be overcome, not a mere preference to be accepted as "the way I happen to be"; while if you were born liking apples but hating pears, usually there would be no reason to fight that preference.

A rational person can neither blindly accept every urge as an unchangeable given of his or her nature – nor stubbornly fight that nature for no reason.

To put it in philosophical terms, the morality of sex must be based on the metaphysical nature of man, that is, on the essence of human nature as it is today. Man is a rational being ("rational" in the sense of having the power of reason), who therefore must live the life proper to a rational being: and what is proper includes those things in our physical and psychological make-up which are objectively good for human life and happiness.

Ancestors & Descendants

Evolution is driven by the requirements for successful reproduction. The first steps in that are mating and conception. Conception is an automatic, purely physiological consequence of mating: but mating is voluntary – and not without its costs and dangers (e.g., energy and opportunity costs in finding, courting and winning a mate; and dangers from predators and even your mate itself). As the voluntary sine qua non of reproduction, mating has attracted a lot of attention from evolution, which has made it a highly desirable activity: with both strong motivators (libido, desire, lust and love) and strong rewards (intense physical pleasure and emotional fulfilment).

One consequence of our intelligence – the biological precondition of being a rational being – is the very long childhood needed to provide time for mental development and learning. When you multiply that by the number of children, the investment of time and resources means that raising a family is very difficult and often impossible for a lone human in a pre-industrial society, in which the average personal productivity is low even without the encumbrence of young children.

(The following discussion is in the context of such pre-industrial conditions, which is how humans have lived throughout almost all of our millions of years of history as a genus: our formative years, as it were. While the circumstances are better in an advanced society – especially, an unaided parent can now raise children successfully – the emotional and psychological traits humans acquired from those millennia are still with us.)

The crucial facts of human biology in this context are that women give birth and make milk, and men are generally larger, stronger and more aggressive. As a consequence of the former, women are the primary immediate care-givers for children. As the ones who give birth, they are the ones who must carry the unborn child for 9 months; as the ones with the milk, they are necessarily the primary carers up to weaning; and they remain the "logical" primary carers after that while the children are young and still relatively vulnerable (logical both as it is simply a continuation of the existing arrangement, and because it is safer for the children to remain near their mother and the other children, than trying to keep up with the more mobile, aggressive and risk-taking men).

The men, on the other hand, have the freedom, ability and aggression to be the protectors, the warriors, the hunters, and the providers of prized, valuable but difficult and dangerous foods, notably animal meat. Of course, even in the stone age women were not helpless, gathering much important food etc.: but they were relatively helpless late in pregnancy and while nursing, encumbered by children thereafter, and of course physically smaller and weaker.

A related physiological fact is that babies are difficult and expensive for a woman to produce, from the nine month pregnancy to the years of infancy. But while babies are expensive for the women who bear them, sperm is cheap for the men who father them: they could easily impregnate hundreds of women per year.

The Trouble with Babies

From these facts distil three factors which have determined the essence of the relations between the sexes.

First, most people desire, value and even need sex. That is a consequence of evolutionary inducements as discussed above.

Second, children take a lot of effort and expense to rear: but they must be reared. That too is an imperative of evolution. The genes of the childless die with them.

Third, while women are the primary direct carers, they can't do it alone. That is a consequence of the expense: and the crux of what the sexes are to each other.

(The second factor above is why we love our children. You have only to see the haggard look of the average new parents, or yourself be the victim of the incessant and insistent demands of young children, to see that without that love, most babies wouldn't survive their first year – especially in a pre-rational therefore pre-moral species. You have only to feel the remarkable strength of the bond normal parents feel for their children, to see why they do.)

These three factors combined are the origin of the relations between the sexes, and from that, the origin of sexual morality – and of the temptations to break it.


Since children are so much trouble, but they must be raised, but their mother can't raise them alone, someone must help. In humans, that someone is the father (while other relatives can and do help, the father is the main helper in the cultures I'm aware of). Because children are so expensive to those who provide their care, genetically speaking it is only his own children that a man would want to raise. While a male has a motive for tricking another male into raising his children by impregnating the other's partner, for the same reason there is a strong motive for making sure the ones he raises are his. So in general, if his children are to be raised successfully, it is he who must help do it.

Since the time from the birth of the first child to the maturity of the last is so many years, this is a long-term commitment.

The result of this, as evident in most families and human societies, is the long-term bond between a man and a woman, and the love of parents for their children and vice versa. This is the glue which holds the family together and which motivates the mutual concern and exchange of values that is required for successful human reproduction.

This, then, is one of the basic evolutionary causes of the emotional and psychological basis of human sexual relationships: men needed women to bear and care for their children, and themselves had to be protectors and hunters for the family if those children were to prosper; women needed men to father their children and to be the family's protectors and (partial but crucial) providers.

Choices & Values

In a sexually reproducing species, the survival of your offspring depends not only on your own genes, but on those of your partner. In a species with dual parental care, their survival likewise depends not only on your own abilities, but on those of your partner. So the choice of partner is very important. And when it involves a long-term relationship, it is even more important to choose well.

It is this fundamental of human reproductive biology – choice of a long-term mate – coupled with the differing roles of male and female in that relationship, which is the evolutionary basis of human sexual psychology.

Mate choice in humans as we are now involves the conscious choice of values by a rational being: but those values are rooted in the psychological preferences inherited from our evolutionary history. One's rational (or irrational) decisions in that regard are made from within our psychological context, not independently of it.

Note that although both parents will want to choose the best partner they can, an asymmetry remains. In our evolutionary history it was more critical for the woman to choose well: partly because if something went wrong, it was she who was likely to be left literally holding the baby (being the primary carer), partly because the men had greater opportunity for new or supplementary relationships (given the ease of fatherhood vs motherhood – an advantage accentuated with age), and partly because she was weaker physically and so needed the man in a way he didn't need her (as warrior, hunter and protector).