The 10.000 Year Explosion and the evolution of personality

The 10,000 Year Explosion by Gregory Cochran and Henry Harpending is definitely one of the most intriguing books on human evolution I have ever read. Despite being more than 10 years old now, it has proven to be quite accurate in many of its hypothesis (e.g. our genetic Neanderthal admixture).

While many people will be aware of the fact that the agricultural revolution has brought along genetic changes regarding our diet, few will be aware of the fact that it also has brought along psychological changes. The authors discuss the human serotonin system which might have made human “tamer”. This tameness would have made children more compliant in helping with the chores (hunter-gatherer children are not forced to work) and being taught the required skill. It also would have made adults more compliant to live in a more hierarchical and less egalitarian society.

The authors make it clear that evolutionary psychologists got it wrong when they denied that any significant evolutionary changes could have happened in the past 10.000 years since the advent of agriculture, treating all people like hunter-gathers. In fact, the authors argue that agriculture has led to Bourgeois virtues: being able to defer gratification, planning ahead, being conscientious and hard-working. All these traits helped early farmers survive and reproduce. On the flip side, they also had to become less egalitarian and became less open to change (experience/ideas in the Big 5), as their work involved more routine than that of hunter-gatherers (e.g. farmer types would be less open to trying new foods as adults).

With the advent of farming and pastoralism status could be acquired with the accumulation of more material reproductive resources and be translated into more offspring. Of course, the sharing-caring attitude of hunter-gatherers would have been an obstacle and also reduced to a more in-group sociality. Conscientiousness, a love for routine and adherence to tradition and community rules were advantageous traits of early farmers as these traits increased their productivity.

Even though the majority of people in the past 10.000 years practised farming, I would argue that not all of these humans had a farmer personality. A lot of hunter-gatherers and pastoralists (the latter often through raids, like the Indo-Europeans who dispersed throughout Eurasia from the Asian Steppe) were assimilated into the farming cultures, even though these might have had a harder time living in a farmer society. Many hunter-gatherers and pastoralists (e.g. gipsies with pastoralist origins) still refuse to integrate into modern society, which with its 9-5 routine jobs and status-orientation (keeping up with the Joneses)  is mostly a farmer world.  

Like Gregory Cochran and Henry Harpending, I have argued that our recent environments have shaped our psychology, in particular, our ancestral subsistence economies: hunting-gathering, farming and herding. The resulting personality groups correspond to the Myers-Briggs types as well as groups Helen Fisher has found analysing dating sites:

Due to assortative mating, the personality traits of each group may have remained somewhat bundle, (e.g. hunter-gatherers: fiercely egalitarian, hyperfocus when interested, perhaps even more monogamous and less likely to accentuate gender display. Here is a table with likely genetic traits  for hunter-gatherer and farmer personality types:

hunter-gatherer	farmer
High on personality trait “openness”, (often) low on “conscientiousness”	High on personality trait “conscientiousness”, low on “openness”
Strongly (actively) egalitarian	status-seeking
Tendency towards out-group sociality, more accepting of diversity (e.g.  different sexuality, refugees, etc.)	Tendency towards in-group sociality (identifies more strongly with a core group, like family, religious group or sports team)
More liberal ideology	More conservative ideology
Less sexual dimorphism	More (display of) sexual dimorphism
Later onset of puberty	Earlier onset of puberty
More monogamous tendencies	Less monogamous tendencies
Tendency to wanting fewer children	Tendency to wanting more children
Relaxed child-rearing attitude	Authoritative child rearing, “helicopter parenting”
more likely to become night owls	Early risers
“Lazier” (when it comes to physical work and chores)	More hard-working
highly rebellious when feeling personal freedom and values are threatened	individualistic, but also more conformist and highly loyal to their core group
Less interest in small-talk and gossip	Higher interest in small-talk and gossip

Gregory Cochran and Henry Harpending also discuss possible genetic evolution leading to the scientific revolution, leaving the question unanswered in the end, however. Anyone well familiar with the Myers-Briggs test is well aware that most famous scientists from Galileo and Newton to Darwin and Einstein were of the NT or Helen Fisher’s “director” type. So, the scientific revolution was mainly a hunter-gatherer phenomenon. The reason can be found in trait “high openness to ideas”, which correlates with intelligence. Why should hunter-gatherer types be more intelligent than farmer types? The answer might lie in an evolutionary arms race: being more egalitarian than the average person can be highly disadvantageous for one’s reproductive potential, so higher intelligence and/or higher levels of social wariness (neuroticism) might have evolved in hunter-gatherer types in the past 10.000 years.