The three foremost reasons that people give for having sex are love, pleasure, and babies. No one ever mentions the survival of the species, or evolution. What they fail to see is that the fitness for survival of an individual – eat, drink, sleep; fight or flee – only makes sense if this fitness is passed on to the next generation. And the link between fit genes of a man and a woman and the next generation is making babies. In this process, the genes are not only passed on but also reshuffled, duplicated, and altered. Biology has programmed for Homo sapiens’ evolution a method of sexual attraction and selection, adaption and variation, and heredity that, over the generations, creates optimal genetic change like with no other species. And to ensure that we make babies, the biological procreation program has installed in us the primal instinct of sexuality, the sex drive.

So, what about love? By the end of the seventies, Tina Turner had divorced her husband who had lost his way in sex and drugs and rock’n’roll. She started a solo career even more successful than with the ‘Ike and Tina Turner Revue’. In 1984, she had her first big hit: ‘What’s Love Got to Do with It’. It’s on the list of the ‘Greatest Songs of All Time’. And in that song, she sang: “You must understand, though the touch of your hand, makes my pulse react, that it’s only the thrill of boy meeting girl, opposites attract, it’s physical, only logical, you must try to ignore that it means more than that. Oh-oh, what’s love got to do with it? What’s love but a second-hand emotion?”. There is a portion of autobiographic disappointment in the song, but she is basically right. Instinctive sexual desire, love and pleasure are complicated and intertwined. It’s a mixture of candle-light dinners, wine and roses – and hormones and chemical reactions influencing the nervous system and the brain. Reptilian brain, mammalian brain, cortex. To the extent that love is understood as attraction that involves care for the other, sexual appeal, and duration into the future, it is a commitment device for human pair bonding. Attachment. All part of nature’s plan to ensure that humans produce babies. In many cultures, the celebration of romantic love, the value of monogamy, and the institution of marriage have socially reinforced the biological pair bond.

In the Middle Stone Age, human sexual behavior was still rudimentary, certainly not considered to be a matter of love. Emotions, language, and song were not yet developed to the point that humans would talk or sing about sex, love, pleasure, or anything else. More or less like their ape relatives, they would just follow their biological reproduction program. Nevertheless, our human ancestors seem to have understood that the promiscuity of the bonobos and chimpanzees as a mating system has disadvantages: With promiscuous copulation, there is no bond between the mating partners and, as offspring cannot be attributed to a father, there is no father-child bond. As a result, the entirety of parenting is assumed by the mother. In chimpanzee and bonobo societies, there are only single mothers, and the only family ties are the mother-child bonds.

The introduction of pair-bonding between males and females was a decisive step in human evolution. It may go as far back as Lucy and our hominin ancestors but was certainly established by the time of Homo erectus. The human pair bond is described as a mating unit not only for the purpose of reproduction but beyond that for the bi-parental care of offspring. It extends to companionship and can become a life-long monogamous partnership. Human pair-bonding is biological and came about by sexual selection: Females’ choice of mating partners shifted toward lower-ranking males who were ready to share resources with them and were up for parental investment. And for certainty of fatherhood, males became willing to take responsibility for their partners and offspring. Paternalistic provision and protection. The females would return the favor by nurturing the mate and offspring, and sexual fidelity. But to this day, the alpha males remain competitive. While they provide more resources and status, they engage less in bonding and parental care. Overall, humans became the only animal for which the pair bond carries the mating couple beyond one breeding season. And together with the mother-child bond, the pair bond and the father-child bond became the foundation of the family, and human kinship.

From a 2008 interview about sex and HIV in a Canadian newspaper: Mohammed Ali thought it over. After long and obviously hard consideration, he concluded that it must have been 100,000. 100’000 women, that is, sex with 100’000 women. Ali had worked as a truck driver for 30 years on the highways that lead from the coast through Kenya into the heart of Africa, on the western side of the Great Rift Valley. And now, he claims to have had sex with 100’000 women. A quick calculation will tell you that over the 30 years of his driving, that would make more than nine women a day. So, it's probably something of an overstatement. But it speaks to the culture in which Mr. Ali has spent his working life: "There are so many women on the road, and they are tempting, the way they dress is very alluring and I'm very tempted by them", and male promiscuity is traditionally viewed as positive, a reflection of masculinity. Such exaggerated storytelling by men about their sexual prowess is well established. Studies suggest that men report many more past sex partners than women. For your curiosity, where you stand: In one survey of 15’000 people, aged 17 to 74, the score was 14 to 7. And in another survey regarding sex partners over a lifetime, it was 10 to 3. Mathematically, also these scores do not add up because, as follow-up studies have shown, prostitutes and hypersexual women cannot make up for the difference.

Half of the women think that humans are naturally monogamous, but of the men it’s only a third. And, as much as science can confirm that the pair bond is an element of human nature, it cannot confirm that humans are monogamous. Innate relicts from the promiscuous times before the pair bond as our mating system linger on. Even while pair-bonded, men will continue to seek opportunities of sexual variety and have preferences for young, fertile, and attractive women. And, to a lesser degree, women will continue to seek attractive men with more resources and higher social status. And when they find a match, biology matter-of-factly calls it ‘extra-pair copulation’. In the Christian West however, promiscuous men and women are prone to derogatory judgement, the women more so than the men. The woman is a ‘slut’, the man a ‘womanizer’. In our modern times, the moral standards of monogamy and marriage seem difficult to uphold. In Switzerland, 46% of marriages are divorced, in all of Europe, it’s 50%. In the USA, it’s 45%. But within five years, half of the divorcees will pair-bond and marry again. In the West, people practice ‘serial monogamy’.

Culture certainly has a bearing on monogamy and marriage, and the social pages of my Kenyan newspapers reveal many behaviors in African sex life that meaningfully differ from the West. In the ‘Heart Advice’ column, one woman complains: ‘My husband has kept his side chick and two children hidden for 10 years’. Meanwhile in the small ads: ‘This sugar mama wants you to romance her life’. And in ‘Personal Finance’, a young man asks: ‘I have two wives, no savings, no car, and earn Sh35’000 (USD 250 at the time). How do I start a car leasing business in Nairobi?’. For sure, the gender binary plays out differently in Africa and Christianity has not succeeded in changing this: African cultures do not attach moral and religious values to sexual activity. Promiscuity, polygamy, transactional sex, holding mistresses, and even prostitution is all widely practiced and accepted. And within all of this, a major difference: In Africa, female sexuality is blatantly free. – And they bear the consequences: The highest numbers of single mothers worldwide are found in Sub-Sahara-Africa. Every third mother is single. When she has more than one child, the children are often from different fathers. In Kenya, Tanzania, and Zimbabwe, more than every second mother is single. In Switzerland, it’s one in seven.

Last Sunday, Bilha and I watched the old Monty Python movie ‘And now for something completely different’: Has it occurred to you that talking about human sexuality has brought us into a realm of words beginning with the letter P? To start with, it’s all about procreation. Preventing pregnancy, the pill undermines this ultimate purpose of having sex. The pair bond and paternal childcare distinguish human sexual relationships. We note the promiscuity of our ape relatives the chimpanzees and bonobos, and the polygamy of the gorillas, and both, promiscuity and polygamy, are also known amongst humans. Some feminists condemn the penis and penetration as agents of patriarchy. And then, we have prostitution, perverts, and pornography. But platonic love and parthenogenesis – of which I once thought that it applied to crocodiles – have nothing to do with sex.