Imagine an alien naturalist – an extra-terrestrial scientist come to our world to study life on Earth, to observe us, and our place in the grand scheme of nature. The scientist would see a world bursting with life. Vibrant cells everywhere, some organised into larger bodies, but all running off coded messages inside those cells, and all interdependent. It can see through time and sees that life has existed for eight-ninths of the planet’s existence, and during that time, has been continuous, with a few blips but no breaks. And it would see that none of those cells or organisms is permanent. All produce new versions of themselves, and thus the unbroken chain of life continues.
The alien scientist takes a special interest in humans, both our biology and our behaviour. It notes that humans are large (but not the largest), plentiful (but not the most abundant) and everywhere (though only very recently). We are not the most numerous, by number or as representatives within our self-styled taxonomy. The mammals – hairy creatures that produce milk to nurture their young – are a small group of organisms on Earth, with only around 6,000 types known, one-fifth of which are different styles of bat. There are a few types of primate, even fewer large apes. None of them is as numerous as Homo sapiens, the only remaining great ape designated ‘human’ that strode Earth’s lands for the last few million years.
There have been a few members of the genus Homo over the years, though no definitive number of discrete human species has ever been agreed upon. Some are new discoveries in the first few years of the twenty-first century, such as the diminutive Homo floresiensis, the so-called island-dwelling Hobbits of Flores in Indonesia, or Homo naledi, a slightly larger primitive people mysteriously found deep in a crow-black labyrinthine cave in South Africa in 2013; both coincided with versions of us in time, if not in space. Then there’s the Denisovans, a people known from only a tooth and a couple of bones, and their entire genome. They haven’t got a species designation, because the way we classify living things relies on anatomy, and those remains are not enough. From their DNA, we know they were distinct from us and any other humans we know of. What is clear among all this murk is that we, Homo sapiens, are the last surviving humans, and with no plausible prospect of us diverging into new, sexually incompatible populations, we will be the last humans.
Despite our apparent ubiquity and success, the curious scientist would see that we are not creatures with great durability, at least so far. We are a tender 300,000 years old; though our larger familial group – the great apes – has endured a much sturdier ten million years. By comparison, the dinosaurs, which we sometimes mock for not having survived an interplanetary impact the like of which has not been seen for sixty-six million years, were a class of animal whose tenure on Earth far outstrips our own; we have not had to face the consequences of a meteorite the size of Paris. In fact, the longevity of dinosaurs was such that we humans are closer in time to the mighty Tyrannosaurus rex, than the mighty Tyrannosaurus rex was to the iconic stegosaurus.1
In trying to piece together universal rules about why all of these creatures behave as they do, the alien would see a diverse range of abilities and lifestyles. Upon even the most superficial inspection, one aspect of human behaviour would be utterly impossible to ignore. We spend a titanic amount of time, effort and resources on trying to touch other people’s genitals.
If our extraterrestrial researcher is not a sexual being,2 this is all a bit of a puzzle. They note that there are two different types of human for the most part (though throughout history in every culture there have been those who either biologically or by choice are somewhere in between). They see that a large proportion of humans don’t show any particular interest in sex at all until their second decade, at which point almost all of them do. The alien likes data, and observes that once they start expressing an interest, most members of the human species have fewer than fifteen sexual partners during a lifetime.3 They also note that they like touching their own genitals: almost all humans that can masturbate, do.
So, from an outsider’s point of view, sex is a huge, vibrant part of the human experience. Some of the specific actions of genital touching have existed in the sea eons before anything vaguely hairy ever walked on land; in fact, before trees existed, and before the current continents were formed. The alien observes the huge, fearsome, armour-clad, razor-toothed Dunkleosteus, a Devonian fish from some 400 million years ago that copulated by ventrally inverting with its partner – that is to say, an early fishy version of the missionary position that many sharks still go in for today – so that penetration and internal fertilisation can occur (like many living fish, the males also have rather sturdy ‘claspers’ so that they can hang on).
There is an orgy of ways in which genital tactility can occur, in any combination of the two sexes in humans and in other animals, but the act of sexual penetration is very old. Nevertheless, it is one that humans continue to enjoy. The statistician David Spiegelhalter has puzzled on the numbers that describe our sexual lives, and estimates that something like 900,000,000 acts of heterosexual intercourse take place per year in Britain alone, or roughly 100,000 per hour. If we extrapolate that to the seven billion humans alive, it works out at around 166,667 every minute.
Why would this bipedal creature dedicate such industry to physical communion of this nature?
Of course, everyone knows the answer to this question: sex is for procreation. It is for every sexual species. A combination of genetic material supplied in eggs and sperm seeds the growth of new, but subtly different, versions of the same creature. The primary purpose of sex is to make babies. Females wish to have sex with males, and males wish to have sex with females. Between these two pillars of evolutionary necessity, there lies a multitude of sins.
It barely needs saying that not all sexual acts in humans occur specifically to make babies, but we do them for other obvious reasons; for fun, for bonding, for sensory stimulation. The odd thing about the frequency and effort devoted to sex in humans is that our extraterrestrial anthropologist would struggle to arrive at the conclusion that any sexual act was ever followed by pregnancy and the arrival of a small human. In Britain, around 770,000 babies are born each year, though if we include miscarriages and abortions, the number of conceptions rises to about 900,000 per year.
What that means is that of those 900,000,000 British bouts, 0.1 per cent results in a conception. Out of every thousand sexual acts that could result in a baby, only one actually does. In statistics, this is classed as not very significant. We are only considering heterosexual acts of vaginal penetration here, so to include homosexual behaviour, and sexual behaviour that cannot result in a pregnancy, including solitary acts, then the volume of sex that we enjoy magnificently dwarfs its primary purpose. So can we truly say that sex in humans is for procreation?
Humans are different from other creatures. By engaging in acts that don’t directly enhance our own survival, we have loosened the shackles of natural selection. Evolution of humans in the last few millennia has been a complex partnership between our more basic biology and the culture that we have shaped and crafted with our intellect, graft and ingenuity. That has meant that the drive to reproduce, to simply be husks for the propagation of our genes, has been complicated and disturbed, at least compared to what came before.
Nevertheless, no one could argue that we have not been a fecund species. There are more people alive than at any other point in history. Until 1977, all of them occurred following a man and woman having sex.4 The rate of population increase has accelerated alarmingly. We hit our first billion at the beginning of the Victorian era, and our second by 1927. But the gaps between our second and third, and all the way to the seven billion humans alive today, have got smaller and smaller. Most of this is to do with our brilliance at dealing with disease, infant mortality and death, rather than us having a lot more sex. The widespread use of effective contraception does not appear to have significantly dented population growth, though may yet have an impact as we globally attempt to balance available resources with our desire to have sex and procreate. Statistics on our sex lives are hard enough to come by in the twenty-first century, let alone in the past, but there is little to suggest that we are having significantly more sex than ever before.
When it comes to sex, there is a galactically skewed ratio of reproductive acts versus all other sexual activity. When thinking of our sex lives in relation to the rest of the natural world, the question becomes: ‘Is this normal?’ We spend so much time engaging in sexual activity, and yet so little of it results in babies. Sex is a biological necessity, and our interest in sex has clearly evolved well beyond any basic animal instinct. But we are animals. Has our obsession with sex made us different?
1 Roughly: dinosaurs spanned 250 million years until 66mya (million years ago). Stegosaurs: 155–150mya; tyrannosaurs: 68–66mya.
2 Plenty of complex organisms are not. Rotifers, for example, are tiny wormy things, a tenth of a millimetre long, and found almost everywhere there is fresh water. Hundreds of rotifer species are all females, having ditched males as unnecessary some fifty million years ago. They seem to be doing fine.
3 Again, there is not a great deal of detailed data on these sorts of questions. But what we do know is quite revealing. According to the mathematician Hannah Fry, studies have put the mean number of self-reported sexual partners at around seven for heterosexual women and thirteen for heterosexual men, though she notes that some (particularly men) claim many thousands, which means that the mean is not a very useful stat in this case. We also know that women tend to report specific numbers, counting upwards, and men tend to round up, often to the nearest five. Both are valid estimation techniques, but the women’s technique is prone to underestimation, and the men’s is prone to overestimation. Funny that.
4 The advent of in vitro fertilisation was marked by the birth in July 1978 of Louise Brown, who was conceived the previous November. This is still the fusion of egg and sperm, provided by woman and man, so remains sexual reproduction. Some estimates suggest that more than five million IVF babies have been born since. I am sometimes asked if IVF, and specifically selection of embryos free of certain diseases via the technique called ‘preimplantation genetic diagnosis’, will have a significant effect on human evolution. I think the answer is no, because the numbers are relatively small, and only accessible to a tiny proportion of humanity, as it is a technical and expensive procedure.