Overcoming male reproductive greed

The need for a palisade increases the cost of living. Painting by Herbert Roe, 2004, of the The Kincaid Site in Massac County, Illinois.

In bestseller book Guns, Germs and Steel (1997), geographer Jared Diamond launched the theory that geographic conditions explain why some parts of the world are more developed than others. Eurasia became more developed because it had the best wild plants and animals to domesticate, according to the book. The continent also had a good east-west elongation, so plants and animals domesticated in one place could be brought to many other places. In America, animals and plants would not easily travel over the bottleneck of Central America with its warm climate. 

Humans had been in Eurasia the ideal amount of time, according to Diamond. In Africa they had been too long, so the germs had gotten too used to them and developed into too many nasty diseases. The wild animals were too wild to successfully domesticate. In America, the animals were too tame when humans came, so humans extinguished the macro fauna when they arrived. There were few germs adapted to humans, so humans did not develop immunity to diseases from Eurasia, which proved disastrous when the Europeans arrived. In Eurasia, there were animals and plants to domesticate and enough diseases to develop some degree of immunity without keeping population numbers down.

While reading that book, I constantly felt suspicious: Can this be true? Obviously the germs part is: Until the 20th century Africa was sparsely populated because of diseases and the European conquest of America was obviously greatly helped by Old World diseases killing off most of the population before the conquistadors arrived. But the animals and plant theories felt a bit speculative: How can anyone possibly know how wild the animals in Eurasia and Africa were before domestication? Diamond points out that humans domesticate no new wild plants and animals these days. That, according to Diamond, is a sign that there is a real scarcity of wild plants and animals to domesticate. But it could just as well be that successful breeding widens the performance gap between the domesticated and the undomesticated plants and animals. The longer we breed certain species of plants and animals to suit our needs, the less incentives we have to start from scratch with new species. 

It is all about the numbers

For a long time, I remained skeptical of Jared Diamond's plants and animals explanations, without having any rival explanation. Then I discovered the books of Peter Turchin. You know, the guy that explains everything with population density. And there we had it, the explanation: The most advanced human cultures developed in Eurasia, because Eurasia was the most densely populated continent. 

In Africa, nasty diseases kept population numbers down. The Americas got populated only about 15 000-20 000 years ago, so it had less time to fill up. 

The theory of cultural evolution is that societies develop when they compete with each other. The more societies confront each other, the more pressured they become to invent new tricks. Human societies have been shaped by two oppositional forces: Individual selection and group selection. When outside threats are present, people go into group selection mode and stick together against the enemy. When no important outside threats are present, people instead fight each other. In War, Peace and War (2005), Peter Turchin demonstrates how this mechanism worked during written history. He shows example after example of societies that united into bigger military units because of external threats and dissolved into smaller military units when those threats subsided. 

This theory should imply that the most advanced societies developed in Eurasia because Eurasia was the most densely populated continent. In Eurasia, humans had the most occasions to confront one another. That means that Eurasian societies were the most pressured to develop into larger-scale and more efficient military units. I don't know if Peter Turchin ever wrote that. I can't recall where he did, if he did. But that was what I thought after reading Peter Turchin's books about the effects of population density: If population density is that important, then it probably was population density rather than the quality of plants and animals that made Eurasia home to the most advanced cultures.

Back to the jungle

Human history is a dynamic between individual selection and group selection. That is the very essence of cultural evolution. Every step of transition to more selfless behavior from the side of individuals is counteracted by a very strong force of nature: Individual selection. The only reason for individuals to subdue their own competition under the interests of the group is a mortal external threat. Otherwise, the selfish genes always win and we get no civilization. 

Another writer helped me to that conclusion: Napoleon Chagnon, the anthropologist that studied the Yanomamö horticulturalists of the Amazon for 30 years. As far as I know, Peter Turchin never mentions Napoleon Chagnon's work in his books. But I think that their respective theories go very well together. 

The Yanomamö were an example of a small-scale society. Groups normally became no bigger than 150 people. When groups became bigger, they tended to split because of disagreements between group members. Those disagreements centered around the allocation of reproductive-age women. The Yanomamö were limitlessly polygynous. Every man could have as many wives as he could barter or kidnap. Men could be somewhat generous to their close male relatives: Brothers could deserve some wives too, even cousins could. But when people became less closely related, they often competed about the limited number of women rather than cooperate.  

This high degree of disagreement in itself kept population numbers down. About 30 percent of Yanomamö men and 10 percent of Yanomamö women were killed by other humans. Only a fraction of the land available could be used for feeding humans, because most land was situated too close to an enemy village. Because of that, the Yanomamö could never fill their ecological niche. 

The Yanomamö never came up with a cultural invention that put a limit on how many women one man could have. Even less, they invented the idea that the women themselves should have a say. Instead, it was considered normal to be blatantly reproductively greedy. That greed effectively prevented the Yanomamö from building larger-scale alliances. When two Yanomamö groups formed an alliance, the stronger group tended to demand an un-reciprocal exchange of women, so the small group gave away more women than the bigger group. Even worse, sometimes the strong group deceived their allies and kidnapped as many as they could of their women. That way, small groups of men maximized their own reproductive success at the expense of larger-scale cooperation.

This pattern of greedy deception kept Yanomamö societies small-scale. With no higher principle than the fact that all men wanted many women, the Yanomamö couldn't agree with each other.

A pre-Malthusian world 

Napoleon Chagnon's report that the Yanomamö fought over women rather than food was met with fierce resistance in academia, Chagnon writes in his autobiography Noble Savages (2014). Marxist professors assumed that all wars were about material resources. When Napoleon Chagnon reported that the Yanomamö killed each other in raids despite being well-fed, those professors refused to believe him.

What Napoleon Chagnon discovered was a pre-Malthusian corner of the world. Malthusianism only came when men had learned to cooperate with each other to such a degree that all arable land could be used. In order to fill the land with so many people that they starved due to lack of farmland, people needed to stop killing each other at high rates first. 

Peter Turchin describes this as a long process. In Secular Cycles (2009), he writes that in pre-Inca South America, people lived and cultivated on hilltops, because they were too afraid of each other to cultivate in the fertile valleys. Such fear kept population numbers down, because people couldn't feed that many children on hilltops. Only when the Inca empire created peace between the smaller groups, all land could be cultivated and population numbers exploded.

The same was true for the Yanomamö: Swathes of pristine rainforest lay between enemy villages. When villages were at war, they needed a certain distance between each other in order to lessen the threats of raiders. If those villages instead agreed to stop killing each other, they could have filled that rainforest with more fields, staffed by the men who weren't killed in wars. But that didn't happen. Since the risk of lethal raids was high, people needed big chunks of unpopulated land between them. That held the threat of starvation at bay: There was enough land to cultivate and enough prey to hunt around the villages. If people were sometimes underfed, it was because of fear: In times of intense raid warfare, men were sometimes too afraid to hunt. 

Among the Yanomamö, violence held down population numbers before starvation did. The habit of stealing women from each other led to such animosity that people could not deplete their resources. Before a Malthusian condition could be reached, a powerful force of nature needed to be subdued: Male reproductive greed. 

It takes a few coincidences

Eventually, in almost the entire world, larger scale societies with actual armies formed. Those armies forced the remaining small-scale societies to adapt or perish. That way, the ball was set in motion and a process of more intense cultural evolution was kick-started.

For this to happen, male reproductive greed needed to be at least partially overcome by some kind of cultural mutation. That cultural mutation needed to take place in an environment that could harbor a larger-scale society. In summary, for cultural evolution to accelerate into a civilization process, three conditions needed to be fulfilled:

1. A cultural mutation, a meme, that allows men to overwin some of their obstacles to cooperation. 

2. An ecology that allowed for larger-scale settlements.

3. A certain population density so people can not just flee to pristine lands and maintain their old ways.

For that reason it wouldn't matter how many times a meme that allowed higher degrees of cooperation occurred among the Yanomamö. Their living environment didn't allow for particularly dense settlements anyway. Not with the technology they possessed. No matter how well some men learned to cooperate, they couldn't build an army to defeat the others if they remained vulnerable to the traditional raid warfare the others excelled in. 

The process of overcoming male reproductive greed was very gradual and uneven. To some extent, it started already among our early ancestors. Among our cousins, the chimpanzees, males also cooperate to some degree. But only in small groups against other small groups. The chimpanzees live in small, patrilocal groups. Sometimes the males attack males from other groups in a kind of raid warfare. If they encounter an unprotected individual from another group, they kill him. But reproductive competition between males is still the main number for chimpanzee males. Males within the group struggle for the alpha position on life and death. The males who form a group are also often brothers or half-brothers, since they spend their lives in the same group where they were born. 

In every human group, males cooperate better than in every ape group. Humans simply are more cooperative animals than apes, also on the male side. But also in humans, rates of male cooperation have evolved from lower to higher levels throughout history, in all but the most hostile ecologies. 

It did so at different times in different ecologies. First it happened in the most suitable ecologies, like the Fertile Crescent and ancient Egypt. As technology developed, more and more ecologies became suitable. For a long time, northern Europe was too inhabitable for larger settlements. It took thousands of years of technological advances to make really large armies efficient there. Until then, it was populated by smaller-scale chiefdoms most of the time.

In the Americas and Africa, it took longer for population density to develop. Even when cooperative cultural mutations occurred in environments suitable for dense settlements, potential subjects could just disperse and become settlers instead. Eventually, also parts of the Americas became crowded and large scale cultures like the Aztecs occurred. It just happened later than in Eurasia. For large-scale civilizations to occur, a few coincidences are required. Since America was populated later, those coincidences had less time to happen than in Eurasia. 

In Africa, cultural evolution was rife when Europeans came and disturbed: The better-organized Bantu from West Africa were taking over the continent. Starting about 4000 years ago, the agricultural, iron-using Bantu were displacing or absorbing Bushmen and Pygmy hunter-gatherers and Nilotic-speaking pastoralists. That way, the agricultural Bantu increased the population density of the southern part of Africa. If Western colonialism and technology wouldn't have intervened, this process is likely to have continued. Now it was instead replaced by another, much faster process: As Western technology increased the survival of children, above all the Bantu increased their numbers much faster than they would have done otherwise.

When the push towards large-scale group selection once occurred, that unleashed an avalanche of competition. Those of us who are alive today are nothing more and nothing less than players in that ongoing selection process. The intense group selection process began in Eurasia and that gave Eurasia a huge initial advantage. However, our confidence in that advantage should decrease as time passes. We haven't seen the end of it yet.