There is no shortage of information on how we reproduce. Sexual behaviour, pregnancy and child-rearing are all hot topics in all our media. But the coverage is almost always about how we do it – “we” who live in modern, usually Western societies. How relevant is it to look at what we do today if we want to learn about human reproductive behaviour?
Okay, modern Westerners are human too, of course, but we’re only a fraction of the people living on Earth today. And, if you think about the thousands of generations of humans who lived and died before the industrial revolution, our specific ways of doing things seem even less relevant to the big picture of human behaviour. Modern culture has profoundly influenced our lives and strongly influenced our reproductive behaviour. (Think: contraception, drugs to cure sexually transmitted diseases, on-line pornography, internet dating, vaccination, compulsory schooling and laws against hitting naughty children.)
To test Darwinian ideas about human behaviour we need to study people in a wide range of cultures, including cultures which Westerners used to describe as “primitive”, “barbarous”, “uncivilized”, or “undeveloped”. Nowadays anthropologists tend to call them “small-scale societies”, which is more descriptive and less insulting. Reproduction in these societies seems to more closely match Darwinian predictions than that of modern people who have vast resources and very few offspring. Studies of small-scale societies are essential for developing and testing evolutionary theories of human behaviour because their members live in conditions much closer to those which humans experienced for most of our evolutionary history. Small scale societies have culture too, of course, and looking at their behaviour in light of their cultural environments can give us a more general view of human reproduction.
Unfortunately, there are very few truly small-scale societies left. Nowadays, even many nomadic hunter-gather groups have become dependent on their mobile phones. But we can draw on the reports of historians and of anthropologists who began studying peoples living in remote parts of the world well over a century ago.
In the foraging, herding and subsistence farming communities in which humans lived for most of our evolutionary history, people got all their social information (information from other people) by observing and talking to their family and other members of their community. Members of small scale societies have detailed knowledge of the environments they live in and the expertise needed for exploiting them. And their lives were intricately interwoven with the lives of the people in the family and community they were part of. Their interaction with strangers was limited and so was their knowledge of the wider world, although they may have shared plenty of stories about the wider world.
Our ancestors lived in small-scale communities much more recently than one might imagine from a casual reading of history. It’s true that ancient cities like Babylon and Rome were “large-scale” in that elites and city-dwellers had large complex social and economic networks and in some cases written texts. But the population of these cities was tiny compared to today’s cities. And they didn’t last long. Ancient civilizations, dynasties and empires rose and fell without affecting the lives of more than a small proportion of the humans alive at the time. Most of our ancestors lived in small rural communities. They may have traded with people from towns and cities but they didn’t have much to do with them. In his survey of England’s population at the end of the 17th century Gregory King estimated that 80 per cent of the people lived in small villages and hamlets. England was poised to begin its industrial revolution; her wealth, infrastructure and literacy were growing rapidly but in 1700, few English towns, apart from London had a population that reached ten thousand.
Information about the opinions and customs of people living in this time can be gleaned from diaries, letters and other written materials and many places had officials who assiduously kept records of the births, deaths and marriages. In Europe, some records go back as far as the 1500s and supply the basic details of the lives of the rural population as well as people living in market towns and cities. We also have a great deal of information about small scale societies outside Europe, some from historical records and archives and some from anthropological studies of small-scale societies that continued to exist into the twentieth and twenty-first centuries.
The findings of historical and anthropological studies have revealed so much variation in the reproductive behaviour of humans that it hardly makes sense to talk about “human reproductive behaviour”. But they also reveal three important similarities:
- Every human population has beliefs and rules about reproduction that influence almost every aspect of their lives. Within each community people have more or less the same beliefs so, in general, members of the same cultural group have similar behaviour.
There are often large differences between populations, however. For example, many cultures believe a woman should limit herself to sex with a single man so that the paternity of her children can be certain but this belief is far from universal. Several tribal cultures in the South American lowlands believe (or at least they did until recently) that a child is conceived from the build-up of semen from several men. It’s thought best for women to have several sexual partners because babies with more fathers are likely to be stronger. When a woman gets pregnant, her sexual partners and their families are expected to work together to help her feed and care for their young relative (Walker, Flinn et al. 2010). Other examples are provided by beliefs about gaining sexual pleasure in ways that don’t result in the conception of offspring. Same-sex sexuality is considered wrong in many cultures but many see it as a normal, even essential, part of life (Kirkpatrick 2000). Beliefs change over time too. Masturbation was considered sinful in 19th England but 200 years earlier people seem to have thought it normal and necessary (Hitchcock 1997).
Beliefs about what children need and how they should behave also vary widely from population to population and from time to time. For example, it may seem obvious that human breast milk is the best food for human babies but some farming communities in central Europe appear to have had a centuries long tradition of not breast feeding at all, a tradition that lasted until the 20th century (Kintner 1985). Mothers in Upper Bavaria who breastfed their infants were subject to taunts and ridicule from neighbours and threats from their husband. Babies were instead fed “pap”, a thick paste made by boiling together flour, water and raw cows’ milk. Scripts of Medieval Christmas plays from the area depict Mary making pap for the newborn baby Jesus.
- All cultures believe that human mothers need a great deal of help raising children. It’s easy to see why this is the case; any population that didn’t accept this obvious fact would soon become extinct. A single parent (male or female) can’t possibly provide the all the nourishment, care and protection that a human baby needs (Hrdy 2009). Our babies need to grow a human-sized brain and to do this they must be supplied with much more energy than similar-sized mammals with a smaller brain. The largeness of its brain also means that a human baby has to be born at an earlier stage of development than the babies of other apes. A baby human must exit the womb while its head is still small enough fit through the opening in its mother’s pelvis. Newborn humans are therefore much less developed than newborn chimps so they’re weaker and need more care. From the moment a baby chimp takes its first breath, it’s able to cling on to its mothers’ hair and help itself to milk from her teats. This leaves the mother chimp’s hands free for climbing and getting food. Being clingy is essential for chimps because other members of a chimpanzee troop are not just unreliable helpers; they have been observed to snatch away babies and kill them (Pusey, Murray et al. 2007). Chimps are weaned and more or less independent by the age of five and by this time the mother is usually carrying her next baby.
All cultures may recognize that mothers need help but that is where the agreement ends. Beliefs about the kinds of help mothers need and who should supply it vary widely. In modern cultures, people are paid to care for and educate other people’s children and fathers are expected to do some of the hands-on care. The role played by human fathers varies a lot. In many small-scale societies fathers do little direct caring for children but help by providing other necessities such as food, security, and status in the community. The father’s female kin may spend more time with his baby than he does. In a few cultures, the mother’s relatives provide almost all the help and the baby’s father provides nothing more than his genes. And in many cultures, older children provide much of the hands-on care of their younger siblings, cousins, nieces and nephews. The amount and kind of work that children do (child-care and other work) varies considerably culture-to-culture (Hrdy 1999; Kramer 2005).
- All cultures practice birth control. Only modern societies have contraceptive technology but all societies have customs and/or rules that serve to regulate conceptions.
For example, when Nick Blurton-Jones (1987) studied nomadic !Kung hunter-gatherers in the deserts of South Africa in the 1970s and 80s, he found that most women had a gap between their births of about four years. He also found women who left this a gap of this length had greater reproductive success. Four years seemed to be the ideal spacing for producing the most children while giving each child a good chance of survival. The ability of !Kung women to achieve this spacing probably had a lot to do with their custom of breastfeeding babies until the age of four. Breastfeeding inhibits ovulation, especially in women who are lean, as these women were.
Rules about when it’s appropriate for a woman to have sexual intercourse are important regulators of conception. Some cultures discourage a couple from having sex until their youngest child is weaned, thus making it more likely that babies are born far enough apart that mothers retain their strength and babies get adequate care. A rule that only married couples should have sex reduces the chances of a woman having to endure the risks and strain of pregnancy and birth when she doesn’t have the resources or support necessary to give her child a reasonable chance of reaching adulthood. The European records of birth and marriages suggest that most people obeyed such a rule until the mid-twentieth century (Coale and Treadway 1986). Almost all babies were born in wedlock, although in some regions it was common for a woman’s first child to be conceived before her marriage. Humans can experience sexual pleasure without performing the kinds of mating behaviours that lead to conception and a considerable body of historical evidence from many cultures reveals that unmarried men and woman were not necessarily abstaining from sex, just the kind of sex that leads to pregnancy (e.g., Hitchcock 1997; Kirkpatrick 2000).
The records also suggest that until the late 19th century, once Europeans got married, most of them tried to raise as many children as they could. This is certainly the case with Charles and Emma Darwin. They married in 1839 when they were both 30 and Emma went on give birth to 10 children, seven of which survived to adulthood. The Darwins were wealthy with a large house in the country but many couples of more modest means also produced many children. Meanwhile, a substantial proportion of the population decided, like Charles Darwin’s older brother, Ras, remained unmarried.
When the reproductive behaviour of humans is analysed from a Darwinian perspective, a fourth important consistency is observed. By and large, people who live in small-scale societies or who belong to populations that are at an early stage of economic development behave as if they’re striving to maximize their fitness (e.g., Cronk 1991; Low 1993). They aren’t necessarily trying to have as many children as possible themselves, but they’re behaving as if they want to see their genes get reproduced. People who have no children usually contribute to their genetic fitness by helping their relatives and, if possible (if harvests improve or more work becomes available), they usually get married and have their own children. One of the pieces of evidence that demonstrates this is a careful study of births, deaths and marriages in England from 1541 to 1871. The records reveal that during more prosperous times more people got married and more babies were born (Wrigley and Schofield 1981; Coale 1986).
But then it changed. The child-bearing decisions of people who live in modern cultures show no evidence of any effort to maximize fitness (Vining 1986; Kaplan, Lancaster et al. 1995; Borgerhoff Mulder 1998; Goodman, Koupil et al. 2012). Most people in modern societies can afford to raise many children but they choose not to. Many don’t have any children at all.
The change from striving for fitness to not striving for fitness happens very quickly; in some populations it happens in a generation or less. Researchers have learned a great deal about this behavioural change, but not its cause. It’s a mystery that Darwinists need to solve. See: Why do Modern People Have so Few Children.
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