Sex, symbolism and neanderthals
http://www.cpgb.org.uk/article.php?article_id=1004684
Not only did the neanderthals interbreed with our ancestors. These close cousins help shed light on what it is to be human, argues Camilla Power of the Radical Anthropology Group
Did the neanderthals go through a symbolic revolution? The question helps us understand what exactly we mean by ‘human revolution’. We can certainly learn a lot by comparing neanderthals with modern humans and establishing why our evolutionary outcomes were so different.
Neanderthals are, of course, our very close cousins, more closely related to us than any other species. Given recent genetic evidence for some level of interbreeding,[1] they can be considered as a human population anyway. Analysis of mitochondrial DNA from neanderthal bones found in Croatia suggests our most recent mtDNA common ancestor lived around 600,000 years ago,[2] and that individual was presumably an African hominin of the species Homo heidelbergensis. Our development was closely paralleled by that of the neanderthals. Only 300,000 years ago, our ancestors in Africa looked very similar to the European ancestors of neanderthals.
So I have little time for those who argue that neanderthals were deficient or stupid, with a poor grasp of language, were all brawn and no brain, had no ability to think and plan ahead and died out simply because they did not make the grade. Neanderthals coped in ice age Europe through a series of glaciations for a longer period of time than modern humans have yet existed. Let us see how long our span of existence compares before we judge them deficient.
I will approach the question through behavioural ecology, the science of animals’ direct action on the world - how their behaviour changes in relation to their physical and social environment. The survival strategies of animals are influenced by purely material considerations, fundamentally ones of time and energy. If Marx and Engels were alive today, they would surely be pursuing this branch of Darwinism in order to understand the key features of human evolution.
Why are we here and the neanderthals are not? We must look in particular at symbolic culture and the symbolic revolution - a big and controversial issue. Today there are well grounded arguments that neanderthals, at times and in certain places, were indeed using symbolism. But if so, how did they compare with modern humans?
Let us start by looking at an image of the French Upper Palaeolithic, definitely made by modern humans of around 15,000 years ago (see pic 1). It is from a carving on an easily portable limestone plaquette, which shows women dancing together, with lines drawn between these ‘power points’ of the women - with repeated scoring of lines between their vulvas. It appears to be a cultural representation of some ritual, specifically around menstrual reproductive synchrony. Can we be sure the neanderthals never produced anything like this? If they were as intelligent as moderns, why not?
Now I will go back to evolutionary basics, about how animals use their resources of time and energy in order to replicate their genes. The hard-core Richard Dawkins ‘selfish-gene’ viewpoint focuses on the difference between the sexes in mammals and primates, as each sex has different means to pass on genes to the next generation. We can see the females as a kind of clock, because they have this precious, valuable fertility. For them, replication of genes is an intermittent, rare and very expensive process. In comparison, males produce their sperm relatively cheaply - there is plenty of it all the time, and a little of it goes a long way.
By altering the levels of synchrony of their fertility clocks, we see how females can transform their immediate social environment. If they align their fertile moments, one male can no longer pick and choose many females at their different moments of fertility, while keeping the other males out. Alignment brings more males into the mating system, and if the females need the males for anything, like protection or getting them food, then this is more readily achieved. On the other hand it may be a complete nuisance having all these males around - perhaps the males just compete for the food supply. The main point is that females potentially have the means either to align their cycles, bringing males in, or to disalign and throw most of the males out, leaving only one with access. This is the basic principle of reproductive synchrony, which is a fundamental variable in primate behavioural ecology of mating systems.[3]
That is the theory, but does it work in practice? For many primates, the ability or tendency of females to synchronise definitely exists. It may operate through pheromones or through power structure mechanisms. So a dominant female may be able to suppress reproduction in less dominant females. Alternatively she may synchronise with them and drive their cycles.
We have plenty of field evidence from studies of wild chimpanzees, our closest living relatives. When female chimps are in synchrony, reproductive success - literally measured by ‘fitness’, the ultimate currency of evolution - levels out among the males. The dominant males are unable to keep track of and guard all the females in oestrus - chimpanzee oestrous swellings being highly visible - so the lower ranking males get a chance to mate. In a study by Christophe Boesch and colleagues, when the females are out of synchrony, the alpha male monopolises reproduction almost completely - by as much as 90%. When females synchronise, fitness of the top three males levels out.[4]
Langurs and infanticide
Field studies of hanuman langurs are famous for undermining what Trivers called the ‘group selection fallacy’.[5] These monkeys featured in Sarah Hrdy’s studyon infanticide, where langur males would kill babies other than their own. Usually one male guards his harem of females, while the other males live in bachelor bands. When these bands come into contest with a harem male and a new male takes over, almost his first act is to kill the babies up to a certain age. The females try to protect their babies, but that is difficult. After a very short time they return to menstrual cycling and will mate with the male that just killed their baby. Their babies are dead and this cannot be undone.
The advocates of ‘group selection’ used to argue that the top male kept the population down in order to protect limited available resources. The top male knows best and acts in the interests of the group as a whole. But, if so, how can the females’ resistance to the infanticide be explained? Hrdy, a leading proponent of ‘selfish-gene’ theory, posed a different explanation: that the male is pursuing an entirely selfish strategy. He is trying to ensure that as many females as possible, as quickly as possible, become fertile and available to him. He is trying to change the clock of their fertility in order to do this.
Langurs do not always live in single-male harem groups. There is variability in the natural environment and the way in which females can affect the structure of social groups. Primatologist Volker Sommer and colleagues[6] have followed two distinctive groups, one in Ramnagar in Nepal, and an Indian group in Jodhpur - a very arid environment. Ramnagar fluctuates by season. After the rainy season, when there is a glut of food, many langur females suddenly become fertile. When the females’ fertility becomes aligned, males flood in and we see multi-male groups. One harem male simply cannot keep out rivals. Unlike chimps, langurs do not show any sign of ovulation. Like humans, they can extend their receptivity - when they are interested in having sex - through a large chunk of their cycle: nine days or more out of a 28-day cycle. Generally langurs do not show any sign of menstruation either, so they have a cycle that does not pin-point the timing of fertility, but they are showing that they are interested in sex for a large part of that cycle. The effect is that plenty of males have sex with numerous partners, and they do not know whether the female is fertile when they copulate. Consequently subordinate males have a chance of getting a female pregnant. This spreads paternity among the males and makes infanticide unlikely, as the males do not know which baby is theirs.
The females are winning as far as infanticide goes, but they suffer also. Having too many males around eating their food constricts the females’ ability to reproduce. The females cannot escape the seasonality in Ramnagar’s environment and are unable to avoid the males flooding in when they are all fertile. So there are costs and benefits in the strategy.
This situation is different in Jodhpur. Here too there is a very arid seasonal environment. But the group under study were fed year-round by a local temple community, changing the profile of the langurs’ seasonality. Throughout the year some of the females, not all of them at once, are fertile. One male is able to guard the whole harem. Assisting this is the arid, open country, so the harem male can easily see when he is threatened by approaching males. But in these different circumstances the females, being non-seasonal, avoid synchronising themselves. They want only one male. They help achieve this by staggering their cycles. They enable one male to keep guard over them for a couple of days before moving onto the next fertile female. They do this by giving a clue that they are menstruating, implying that soon the male will need to come and mate them. This ensures that the male knows he is the father of the offspring - which is fine, as long as he is the male in charge. The cost is that if a new male takes over they will lose their babies. This is a huge cost when it happens - langurs take seven months to gestate and over a year to raise and breastfeed their babies. But there are not huge numbers of males around eating their food.
Consequently the Jaipur females, despite suffering infanticide every few years, are - in most years - actually able to have more babies, more regularly than those in Ramnagar. The female langurs are able to vary their sexual signals to manipulate males in different ways in different environments - within a single species. This ‘natural experiment’ with monkeys uses a framework within primate behavioural ecology which will be useful in thinking about the differences between neanderthals and humans.
In spite of being very different primates, the sexual signals used by women are quite similar to those of langurs. A key factor - even if you do not accept complete ‘concealment’ - is the extreme unpredictability of women’s ovulation cycles.[7] Women are designed to scramble information about fertility by putting out all sorts of distracting signals: even considering the way we walk, the clothes we wear, etc. For instance, the ‘copuline’ hormones, thought to make women more sexually interesting to men, are not produced at the time of ovulation, as one might expect, but on an unrelated cycle, confusing the males. Copulines even things out. Men keep trying to work out the timing of these signals, but end up confused. This design in our evolutionary past of concealing any real information about when we are fertile is highly similar to that used by the langur monkeys. They must, as a matter of life and death, conceal information about ovulation.
In the case of our evolution, this results in paternity confusion, which helps the females by encouraging more males to hang around and provide food or protection. It is highly likely that our evolutionary heritage is one of paternity confusion. - this is basically supportive to the old Bachofen/Morgan/Engels argument. This attacks the idea that pair bonding, monogamy or the nuclear family is the standard evolutionary trajectory of humans. Paternity confusion - where more than one male thinks he may be the father of a child and therefore protects it - may have been a better strategy for human females. The use of concealment is a counter to infanticide. But humans are also different from langurs: human menstruation is clearly visible and marks out which females are pregnant and which are not.
Synchronisation
Obviously, we are very different from small monkeys like langurs in other respects, principally, our body size and of course, brain size. Let us look at the development of the brain. Fig 1 illustrates brain size, going back three million years. It shows a big leap from australopithecines to the first species of Homo, which had a brain about twice as big. Then it remains steady for a while, until about half a million years ago, when the common ancestor of neanderthals and modern humans evolves. The brains of this species were about three times the size of the australopithecines. Even two million years ago, the high cost to females of producing large-brained offspring was already an incentive towards concealment strategies as a means of limiting infanticide. And there is also the question of reproductive synchrony.
To fuel increasing brain size and break through the ‘grey ceiling’ of a 700-800cc brain, human females must have had help with child-rearing - some kind of social care system and cooperation. No other primates have broken through this barrier, because the females have to raise their offspring without help. The major candidates for assistance are female kin and males.
How can the females get the males interested in this task? Concealed ovulation helps to a certain extent. If all the females show and align their fertility, several males will be brought into the mating system and have a chance at fertilisation. However, knowing exactly when a female is fertile gives no motivation to hang around after copulation. Synchronised but concealed ovulation has a greater effect. More males are brought in, because they do not know when they have successfully fertilised a female. They are more likely to stick around to discover if this is the case and provide help or protection. This combination of concealing and synchronising ovulation should in theory bring more males into the mating system. Two million years ago in our ancestry, the combination of these two mechanisms may have been very useful for early Homo erectus females.
But, while langurs can bear young annually in favourable conditions, among our recent hunter-gatherer ancestors there was a three- to four-year interval between one birth and the next: a nine-month gestation period and then breastfeeding for two to three years, before beginning to cycle again. That is seen in hunter-gatherer societies today with a sexual division of labour. Our Homo ancestors evolving from australopithecines with their chimpanzee-sized brains probably had a four- to five-year inter-birth interval.
This raises the question of how clockwork-like synchrony could be achieved. If a baby dies soon after birth, the mother is not going to wait three or four years until all the females are aligned in their fertile period, before becoming pregnant again. That would be too detrimental to her reproductive success. She will go ahead and become pregnant again. So there will be a group of females giving birth in every year. This random pattern means a dominant male does not have to guard all the females at once, because they are not all fertile. He can concentrate on the females who are actually cycling in any one year. This gives the dominant male in early Homo groups a high reproductive success rate.
It can be argued, however, that this can be kept in check if the females are highly seasonal: that is, all fertile only once a year (like the langurs in the rainy season). In a seasonal system, any male will have his work cut out trying to deal with more than one female at a time. He must wait until the following year, when more females begin to cycle, before moving on to another one. This means that at least a couple of other males will be brought into the mating system, which would be good for the females. It would be better still if each female could mate more than one male, spreading the chances of paternity around more males, getting a higher number involved in the mating system.
These two scenarios - random vs seasonal breeding - are radically different. We can play evolutionary computer simulations with these two games. In a random pattern where there is no seasonality, a dominant male has so much potential fitness by mating whichever female is currently fertile, that there is no motivation for him to start settling down and staying with one female to help her until her baby is in a good position to survive, before moving on. In the seasonal scenario, where he has only one female a year to breed with, it is in his interest (even for a top male) to stick with her and help her out during the first year of his offspring’s life and give it a better chance of survival, rather than abandon her on the slim possibility of being able to mate again. So there is a radical difference in what males should do, in terms of invest or desert, if the females are in a seasonal pattern, as opposed to a random pattern of cycling.
From two million to 500,000 years ago, while the brain size of Homo erectus remained fairly steady (two to two and a half times chimp size), we can guess females had enough help from female kin and, occasionally during fertile periods, from males. When she was cycling, the males would become particularly interested in her. These periods would coincide with weaning, when gifts of food would be particularly useful and increase the weanling’s chance of survival. Half a million years ago with Homo heidelbergensis, the common ancestor of ourselves and the neanderthals, we see a massive increase in brain size. These large-brained offspring were extremely energy expensive and meant the females needed their mates to start doing some serious work. In the archaeological record, with Homo heidelbergensis we start to find hunting spears, which show they were already hunting large animals.
