Why do humans ever develop?
In general, animals do not develop. They mostly live in a state of semi-equilibrium with their environment. Sometimes they become too many and starve or get diseased, reducing numbers again. However, they don't answer to such shocks through inventing new ways of increasing their food supply.
And actually, humans do also mostly not develop. For most of the 300 000 years the species named Homo Sapiens Sapiens has existed, the individuals of this species have lived lives indistinguishable from their parents or grandparents.
Humans are the only creatures that progressively invented more and more efficient ways to make food. But they only did so once in a while. Mostly they did just what other primates do: Provided for themselves the way their parents taught them to, without the slightest increase in efficiency.
In part 1 of this series, I suggested that male reproductive greed is a strong impediment to growth. In part 2, I described how human populations can avoid developing through keeping population numbers down through murder and warfare between self-interested small groups of men. In this part, I will suggest what breaks this state of equilibrium and makes humans actually develop. The reasoning is strongly influenced by Peter Turchin's thoughts about population dynamics.
It's all about the numbers
It has been theorized that humans developed because of environmental change that occasionally happened. I'm skeptical of that notion. The environment occasionally changes for all species, not only humans. Other species still don't make inventions that transform their societies (as far as we have seen yet). Human societies have changed curiously uniformly independently of each other. For example, agriculture originated independently in several places within a few thousand years. It would require very much of a coincidence if, after all those years of non-agriculture, humans in such different climates as the Levant, China, South America and New Guinea experienced the same environmental shocks within the same short time span.
Instead I believe we carry the engine of change within us: Population growth. Humans have a higher birth rate than the other great apes. We can afford such a high birth rate since our males do not only compete for mating opportunities, but also provide for their children.
Population growth in itself leads to change. If nothing changes between generations except population numbers, living conditions will be very different a few generations apart. While grandparents were well-fed as young, grandchildren will grow up in penury. With a growing population in a static environment, life is not the same across generations. A constantly growing population equals a constant pressure for evolution. War, starvation, epidemics and other disasters are all at hand to take care of the excess population, but humans, both as individuals and as groups, have excellent reasons to avoid disasters by developing.
Of course, all animals have these reasons to evolve in the face of disasters. But almost uniquely in nature humans have the means to actually achieve it. While natural evolution is generally too slow to evade the disaster at hand, humans have the ability to change their technical, social and cultural abilities and thereby increase the carrying capacity of their environments. These man-made environmental changes will then lead to actual natural evolution. By changing their surroundings, humans are shaping and expediting their own evolution.
In most instances of overpopulation in history, humans did not develop. Instead the blind and brutal method to avoid change was used: Violence.
We humans carry the engine of development within us: Population growth. We also carry the brake that prevents development within us: Violence. The only way for human societies to remain the same over several generations is to keep a high enough mortality to keep their numbers stable.
My hypothesis is that development occurs when violence, for some reason, fails to contain population growth.
What could possibly decrease violence? If people are used to killing each other in cycles of revenge, why would they suddenly stop?
One possible explanation is fear of even more violence. According to Napoleon Chagnon, among the Yanomamö there was one unusually big village with almost 300 inhabitants, instead of the usual 100-150.1 Its leader was called Möawä. That man was, in his environment, kind of an effective statesman. He could prevent his village from going through the usual splits in factions because he instilled fear in the villagers, many of whom nonetheless chose to stay because they thought Möawä was good at protecting them. Napoleon Chagnon observed:
"Because of his forceful bearing and martial abilities, Möawä was able to attract a large following and hold it together. This is what I mean when I say that a strong headman can help keep a village large—adding cohesion where kinship and marriage alliances alone fail to do so."2
Möawä had participated in the killing of 22 men, more people than any other man in Napoleon Chagnon's records. According to Western psychology concepts, Möawä was severely deranged. A narcissist, a sociopath, or both. Not only was he a violent tyrant. He was also selfish in an immature and almost caricatured way. Once Napoleon Chagnon visited his village, carrying antibiotics for eye infections that mainly children get. Möawä also happened to have an eye infection and he ordered that he should have all the medicine and the children none of it.
'“Let them all go blind!” he hissed'3
In Ultrasociety (2016) Peter Turchin writes that despotism seems to be something of a rule when societies reach a certain level of development. The adoption of agriculture had no perceptible effect on equality, as long as societies stayed small-scale. Those agricultural societies that developed further, however, tended to become highly unequal and despotic, led by self-proclaimed god-kings that often served blood-thirsty deities with human sacrifices.4
When I read about Möawä, I thought about that observation. Möawä was a member of a small-scale agricultural society. Through being almost unnaturally unpleasant, he managed to make his group a little less small-scale. When people like him appeared in environments more suited to larger-scale warfare, the fear of such psychopaths might have made people deprioritize their personal interests in favor of larger entities.
However they did it, at some point, some people overcame the force of individual evolution and managed to cooperate militarily in larger groups. When some groups of humans finally managed to cooperate on a larger scale, it forever changed the conditions of human evolution.
Such incidents set a ball of change in motion. When one group has stopped its internal quarreling, and grown beyond the usual limits of personal feuding, it becomes a lethal force to all other groups. The better cooperators can now conquer those who are busy fighting over which man should have sex with which woman. Surrounding populations either need to adapt very quickly to meet the threat, or get killed or absorbed by the bigger group. A process of change has started.
That process will go on until either ecological or cooperational constraints are reached. Given the available technology there is always a limit to how many people an area can sustain. And no social model can make individuals forgo all of their individual interests for the sake of the group forever. There will be a limit, but if that limit is higher than before human development has advanced a step.
When one group puts unusual military pressure on surrounding groups, that changes the environment for everyone. It changes the conditions both for group evolution and for individual evolution. What was a winning strategy for a group when all groups were small might not be so when one group has grown bigger and more powerful. What was a winning strategy for an individual in a small, kin-based group might not be successful in a larger group with a more artificial social structure.
The male labor reserve
Large-scale changes of human societies occur when a cultural mutation changes either cooperation structures or subsistence production. If people in one society happen to get better at fighting together, they can conquer or exterminate surrounding populations. If people in one society develop better methods for food production or can just be made to work harder, they can provide for more soldiers and conquer surrounding populations.
One of the most crucial developmental steps for humans was probably the use of the male labor reserve. Under very primitive conditions, when land is abundant, males don't tend to care too deeply about agriculture. Their wives will be able to feed their children rather well, and due to biological realities they will be much more inclined than the men to actually do so. Males thus occupy themselves with hunting and warfare, always on the look-out for new wives.
It is when land gets scarce that males need to engage in agricultural production themselves. Until modernity, the equation is rather rough. Either you use more land, or you use more labor. That is, male labor, because the available female labor has always been used. During prehistory, females worked more or less to their physical limit. The labor reserve lay in the male body. And it was no small reserve! The male body evolved to hunt and fight. But when necessary, the strength that was previously mostly used to kill (animals and humans) could also be used to farm.
The use of the male labor reserve had enormous consequences for the further development of humanity. When male labor was needed to provide children with their basic calories, males had both less incentives and less free time to fight each other for additional wives. As long as the man himself had to provide for his children, he needed to limit himself to the number of children he could support with his own labor.5 Sure, he could try to father illegitimate children. But that needed to be done deceptively rather than as an open strategy. Gathering as many women as possible was no longer a viable reproductive strategy except for the absolute upper class.
While agriculture decreased the number of children men could realistically have, it increased the fertility of women. The introduction of dairy animals made it possible for every woman to give birth to something like 12 rather than six children during a lifetime. Intensive agriculture reduced the interest in polygyny for two reasons: Men could raise fewer children and women could raise more children.
All-in-all, the Malthusian condition made the reproductive conditions of males and females converge. Not completely, but more than otherwise during history. For men just as for women, being a good worker became a key to successful reproduction. A man who worked hard and inventively could significantly increase the survival rate of his children. In contrast to in societies of land abundance, men who actively try to improve agriculture are selected for. The Malthusian condition tilted selection pressures from men who focused on acquiring numerous self-sufficient women to men who invested their labor and wit into providing for their children with one particular woman.
As we all know, this wasn't quite the end of polygyny. While some men worked the soil for the benefit of their children, others enslaved other men to do it. And they also enslaved women to bear their children. However, the era where all men were masters and all women were slaves was over. Men had become irreversibly entangled in subsistence work.
Eternal growth starts here
Male engagement in agricultural work can be seen as the beginning of a long and uneven process that slowly transferred resources from warriors to workers. As a rule in history, the upper class has consisted of warriors and the lower class of workers. Cultural evolution changed that, but only very slowly. It was not until the advent of industrial warfare in the 19th century that power can be said to have finally, for the first time in history, moved from warriors to workers.
This was a significant change compared to most of human history. Warriors have always protected workers. Under the most primitive conditions, males protect females. Under more advanced conditions, a warrior class protects a working class. In modern society the producer class hires a small band of warriors to guard them from other producer societies.
Modern societies are thus geared towards production rather than warfare. The production capacity still gives significant scope for violence, as the wars of the 20th century vividly illustrate. But the power now lies with the workers and societies are organized to serve the needs of the workers rather than the needs of the warriors.
In theory, productive capacity has been important to warfare at least since the bronze age. But this importance has been dwarfed by the needs of a fierce and cohesive warrior class and their tendencies to act kleptocratically. In every society, the ruling class faces a dilemma: Either they oppress their workers too little and get outcompeted by their more extractive neighbors, who will have more resources at hand. Or they oppress their workers too much, making the workers unable to reproduce and invest in the production, almost guaranteeing a future loss to more long-term competitors.
The development of technology has slowly shifted this balance. When the level of technological know-how is low, there is not much to invest in. Very technologically primitive societies tend to be extractive to the point of death. Literally so. In 1970 anthropologist William Divale compiled sex ratio data from 112 primitive societies. He found that among societies practicing war, sex ratios were on average very male-skewed among children and much less male-skewed among adults. The probable explanation Divale found was sex-biased infanticide.
Killing baby girls is the low-tech version of whipping your peasants to death. By doing that you channel your resources to the military (in other words: men) while neglecting the future productive capacity (in other words: women). This strategy works, for both warlike primitive small-scale groups and cruel feudal lords, because at a low economic and technological level it is perfectly possible to steal your enemies' productive resources. Just as small-scale primitive warriors expect to capture women from their neighbors, so the feudal lord expects to conquer productive lands from his enemies.
Groups that employ this strategy force everyone else to follow it. Raising women only to see them captured by your neighbors will inevitably lead to extinction. Just as investing in your peasants at the expense of your knights will lead to defeat at the hands of other lords. It is a zero-sum game keeping everyone stuck at their current level of development.
This cycle can only be broken by new ideas, technical or social. We have already seen how social changes in primitive societies can lead to larger units sweeping away smaller enemies. In the same way new technological inventions can alter the optimal level of worker oppression. For example, with the advent of firearms the feudal lords were forced to lower oppression of especially towns in order to create the necessary economic resources needed for the procurement of expensive cannons.
Real progress comes with the expectation of ever more progress. If it is plausible to assume that there are better weapons just waiting to be discovered then the correct strategy is to refrain from warfare now and instead invest as much as possible in research and development in order to wage war later. Anyone engaging in war at the expense of development might win short-term gains but will inevitably be eliminated later on. If this belief in future development becomes ingrained enough there will be no sense in waging war at all if it comes at the price of less investment. This is, more or less, the state of modern Western societies.
Winds of change
What we have seen the last 10 000 years is that change breeds more change. When the spark has lit a fire, there is no point of return.
Essentially, the process of change consists of kick-starting group evolution at the expense of individual evolution. The reason why change is so sluggish in early, small-scale societies, is that individual evolution is a very strong force. What is needed is the beginning of group evolution. That happens very seldom, since the force of individual selection needs to be subdued in at least one group.
A rare combination of circumstances is needed to outcompete such a strong force of nature as individual evolution. One set of chance occurrences is needed for members of a group to switch from in-fighting to larger-scale cooperation. Another set of occurrences is needed in order to make males invest and compete more in the subsistence department and less in the zero-sum violence department. A third set of occurrences is needed so that the higher degree of cooperation occurs in an ecology where there is any fruitful ground for it. It took quite a bit of time for all that to happen. But eventually it did, independently in different parts of the world.
Napoleon Chagnon, Noble Savages: My Life Among Two Dangerous Tribes - the Yanomamo and the Anthropologists, 2014, page 386
Napoleon Chagnon, Noble Savages: My Life Among Two Dangerous Tribes - the Yanomamo and the Anthropologists, 2014, page 401
Napoleon Chagnon, Noble Savages: My Life Among Two Dangerous Tribes - the Yanomamo and the Anthropologists, 2014, page 403
Peter Turchin, Ultrasociety: How 10 000 Years of War Made Humans the Greatest Cooperators on Earth, 2016, pages 146-148
See for example Gregory Clark, The Son Also Rises: Surnames and the History of Social Mobility, 2007, chapter 6. Clark has demonstrated that in England during the Middle ages, richer farmers had more children and grandchildren. Working harder and more efficiently was one way to become richer.