A bird of paradise, for instance, is hampered by its long tail and will find it hard to flee from predators, but because females find the tail attractive, they will always pick a partner with the biggest, brightest tail. As a result, their descendants have longer tails, and over time male the birds will evolve larger and larger tails. In humans, an upright posture and the fact that we are not covered with fur draws attention to men's sexual characteristics which, again, may have been selected through female choice.
Dr Timothy Taylor, an archaeologist from Bradford University, says, "in a nutshell, humans have managed to pull ahead of the rest of the animal world by effectively opting out of Darwinian evolution, and I would argue that for the past four million years the human line has been able to consciously separate sex from reproduction." Taylor, who only recently completed his PhD, has already won a British Archaeological Award for an episode of the television series Down to Earth. His new book, The Prehistory of Sex: Four Million Years of Human Sexual Culture, is likely to be equally popular. In it he argues that much of the evidence of our ancestrors' sexual past has been misinterpreted or simply secreted away in museums and research centres because of the prudishness of historians and archaeologists.
Even today many relics are out of bounds to the general public. The Venus figurines from Willendorf, in southern Austria, are a case in point. The earliest surviving sculptures, they are only a few inches tall, and were carved from stone 30,000 years ago during the Ice Age. Naked, large breasted, fat and faceless, the Venuses have puzzled archaeologists for years but prudishness has disguised their true function, says Taylor.
One hypothesis is that they are images of a great goddess relating to a period of matriarchy, a theory that has been popularised by novelist Jean Auel in her best sellers The Clan of the Cave Bear and The Mammoth Hunters. However "the widespread imagery of the Virgin Mary today does not demonstrate that the Pope is a woman," says Taylor - "the statuettes could be telling us something quite different".
His suggestion is that they were carved by men, for men. "The essential feature of the Venus figurines is that they are dur-able. The smooth-worn surfaces of many of them suggest that they were handled often and were passed around." In short, they were the equivalent of Ice Age pornography. They reflect women as a commodity, to be given to other men.
If the figures were sculpted by women, and were expressing their own sexuality, Taylor feels sure they would have had faces and clitorises. But would they? One of the major sexual differences between us and other primates is the hidden nature of female genitalia. To depict the clitoris without making a woman look as if she were preparing for a gynaecological examination would be hard for a sculptor today, never mind the first sculptors in history.
There are other similarly shaped figures from Kostienki in Russia which show women with their hands tied or with straps round their breasts but no other clothes. These fur straps do not represent warm clothing. "My necessarily subjective interpretation of these sculptures is that they are explicitly sexual, sharing themes of objectification and possession," says Taylor, "A sculptor who can depict hands tied together has a pretty good notion of how hands actually are tied together." However, the Ice Age artists didn't necessarily do everything they drew: one example of rock art shows a man on what look like skis having sex with an elk.
Despite the fact that women were portrayed in a passive manner there is, according to Taylor, some evidence to suggest that they were as sexually aware as modern women. A Neolithic figurine which was found at Hagar Qim in Malta has always been interpreted as a recumbent woman about to give birth. In fact, this posture is one that has only been adopted comparatively recently, and on closer inspection it is obvious her belly is only slightly swollen. The figurine has her hand on her vulva: "She is masturbating, one hand languidly supporting her head," insists Taylor.
During the Ice Age many explicitly phallic-shaped batons were also carved. These have usually been considered to be ritual objects, or spear straighteners. "It seems disingenuous to avoid the most obvious and straightforward interpretation," says Taylor. He believes they were dildoes. No doubt out of a false sense of modesty, pictures of these objects are rarely published with dimensions, but those that do have measurements attached to them fall within the range of modern appliances. The first graphic depictions of these sexual devices are found on Greek pottery from the fifth and fourth centuries BC, but there is no reason to suppose that they were unknown to our Ice Age ancestors - especially as other primates occasionally use tools in the same way.
Images and carvings of the penis were predominant during the Ice Age, but disappeared in the Mesolithic, only to resurface by the Neolithic. Some of the graves found at Varna on the Black Sea coast contain skeletons buried with a wealth of riches. The most striking is a skeleton complete with a penis sheath made out of gold. It wasn't some fancy condom - there is a hole in the tip. Taylor believes that it may have been akin to a Renaissance codpiece. "It was clearly a piece that was made to be seen - gilding one's penis is hardly modest."
In the Beaker period (2600-1800BC) gender began to be clearly marked in burial practices. In Beaker graves, men are typically accompanied by a little copper dagger and are buried facing south. Women on the other hand are buried facing north and with pottery objects rather than metal implements. However, Taylor says, "some biologically female graves have also been found with copper daggers, suggesting that as soon as a standardised sex-gender burial practice was esablished, it was subverted by those who did not fit into it easily."
A thousand years later, there is strong evidence for transvestism. The Scythian nomads of the Black Sea steppes were a ferocious warrior elite. According to Hippocrates, they were also impotent. Years in the saddle had given them what the Greek philosopher Herodotus referred to as "female sickness", a complete loss of functional manhood. Herodotus described them as "androgynous" and maintained that many became shamans or prophets and took to wearing women's clothes.
There is even evidence from Ovid to suggest that a fuller transformation was intentionally wrought as the Scythians drank mare's urine. "Premarin", an extract of pregnant horse urine, is marketed today for male-to-female transsexuals as part of their hormone therapy. Rich in oestrogen, it can suppress beard growth and help breasts develop. Taylor adds, "Any subsequent work conducted in the light of the Greek written evidence would have to take into account the fact that the skeleton of a biological male who had drunk pregnant mares' urine out of a ritual container all his life might well be difficult to recognise as male by today's standards."
We are beginning to realise that hormones from animals and plants were used by our ancestors, most commonly as contraceptive devices. It is a myth that ancient humans had no idea of the connection between sex and reproduction: after all, some female orang-utans have been observed to eat certain plants which make them ill, but might possibly induce an abortion (orang-utans, along with mallard ducks and dolphins are one of the few species where it is possible for males to rape females).
That plants have hormones which can affect humans and animals was not scien- tifically accepted until earlier this century when oestrogen was found in willow and other female hormones were discovered to be present in date palms and also pomegranates, all of which can prevent or induce menstruation, reduce PMT or function as contraceptives. Queen Anne's lace, a parsley-like plant that is related to the carrot, is a strong "morning-after" drug.
The Ayurvedic system of medicine, which comes from the Indian subcontinent, uses about 75 plants, 28 of which it is known can induce abortions. There is even evidence to suggest that men took contraceptives: Dioscorides, a medical writer in the first century, describes a drug to make man barren derived from a plant which he calls periklymenon - probably honeysuckle. Ancient Egyptians, however, created a potential spermicide that was not made from plants but a mixture of sodium carbonate mixed with crocodile droppings.
This lore has to a large extent been lost. Taylor believes that women started to lose control over their own fertility during the advent of farming. Farming is usually associated with people settling in one place, greater productivity, an increased division of labour into male and female roles, and also polygyny - where the wealthiest men in ancient societies were able to marry a number of women. Far from being cast out of Eden, we turned ourselves out, says Taylor.
Taylor's fascinating, and often amusing account of our journey from Eden seems to me to contain two major flaws. Firstly he argues that scientists were biased when they examined archaeological remains. But are we any less free from our own biases? Furthermore, it is often unclear what exactly is taking place in many paintings and carvings, much less what they actually mean. Eminent scientists still argue, for example, whether the Ice Age "Grimaldi" figurine is a depiction of an hermaphrodite or two people having sexual intercourse.
Secondly, it seems perfectly rational to believe that as a species we are affected both by our culture and our biology, but Taylor argues that this interplay between the two forces began four million years ago when we first recognised the difference between sex and reproduction. However, the first evidence for this comes from the Ice Age, which leaves a short- fall of three and a half million years to account for.
Appealing to evidence from other animals can, at best, only be suggestive. The majority of species only have sex when the female is in season and there is little evidence that animals play the kind of sex games that we do. The exception is the pygmy chimpan- zee. All members of the troop, from the youngest to the oldest, will have sex with each other, male to male, females with females, and in mixed groups. It is thought that this year-round sexual activity promotes harmonious relationships. Females sometimes trade sex for food, a fact which has led to many spurious arguments about the nature of human sexual relations.
If pygmy chimpanzees have sex all the time, maybe they are incapable of separating sexual pleasure from the act of reproduction; in any case, how can we ever truly know if a chimpanzee knew where babies come from? More importantly, chimpanzees have been evolving for the past four million years too - no one can tell what their ancestors did or did not do to promote peace in their troop, and they certainly haven't left us any rock art to speculate about.
What can be said is that from the first daubs of paint on cave walls to today's cybersex culture, our own species has been continually obsessed with sex.
'The Prehistory of Sex: Four Million Years of Human Sexual Culture' by Timothy Taylor will be published by Fourth Estate on 7 October at pounds 18.95.Reuse content