Humans are one of the few mammals known to have inter­course even when the female is not in estrus (the fertile period in the female’s repro­ductive cycle).

Intel­li­gent social animals learn that cooper­ative beha­viour can be far more successful than that of any indi­vidual alone. Thus human sexu­ality has evolved beyond the imme­diate needs of repro­duc­tion to allow for the forging of emotional bonds between part­ners vital to long-term sexual rela­tion­ships.

We have sex for the following reasons:

• recre­ation: enjoy­ment of sexual pleasure;
• bonding: emotional intimacy to support longer-term sexual rela­tion­ships (deferred repro­duc­tion); and
• repro­duc­tion: directly seeking to achieve pregnancy.

Indi­viduals are motiv­ated by each of these to varying degrees. Men are more likely to benefit from enjoying sexual pleasure. After all, only men are motiv­ated to pay for sex. Whereas women are tend to benefit from the emotional intimacy that keeps a man motiv­ated to support the family.

Repro­duc­tion is the main purpose of sex

With all the hype about sexual pleasure it is easy to forget that the PRIME purpose of sex is repro­duc­tion. This involves not only a man impreg­nating a woman but also the provi­sion of a home in which a child can reach maturity. Despite drives for sexual equality, women are still the home-makers and need to identify a man dedic­ated to their family goals.

Even today a woman bene­fits from having the protec­tion of a strong and capable man. So a woman chooses a man who is likely to be able to protect her and a family against the threat from other human males as well as other dangers. Sex provides an emotional intimacy that makes a rela­tion­ship more stable and more capable of sustaining chil­dren in the future.

If women wanted sex the same way that men do, they might be tempted to have sex with many different men even when they have chil­dren. But who would support them while they are raising all the resulting chil­dren? A man wants to know that a child is his before he is likely to be willing to contribute towards its upkeep.

A human female has to be able to offer a mate the sexual inter­ac­tion he needs so that he does not seek sex else­where. Now we might think that Nature would ensure this by causing sex to be equally pleas­ur­able for men and women. The fact is that there is no need for this because women already have enough incentive: the survival of them­selves and their children.

‘The Duchess’ (2008) stars Kiera Knightley as the Duchess of Devon­shire (1757 – 1806). The story portrays the duchess in a love­less marriage under oblig­a­tion to provide a male heir for her husband. She falls in love with another man but when she tries to leave her husband he gives her a choice. If she leaves with her lover then she loses the custody of her children.

Given the choice between sexual pleasure with the man she loves and her chil­dren, she chooses to raise her chil­dren. Many men are perplexed when women lose interest in sex once their family is complete. Ulti­mately, a woman gets the emotional intimacy she needs from her chil­dren at a time in life when men are often more dedic­ated to their own personal goals.

Natur­ally there are excep­tions to the dedic­ated mother. Gener­al­isa­tions are not intended to categorise people abso­lutely but simply to provide possible explan­a­tions for different beha­viours between the sexes. My sugges­tion is that the import­ance of orgasm and espe­cially enjoying sexual arousal with a lover is gener­ally lower for women than it typic­ally is for men.