More on this book
Community
Kindle Notes & Highlights
Started reading
July 31, 2025
The Difference Between a Trait Being Inherited and Having a High Degree of Heritability
What do genes have to do with humans averaging five fingers per hand? Tons; it’s an inherited trait.
While average finger number is an inherited trait, the heritability of finger number is low—genes don’t explain individual differences much.
it’s not meaningful to ask what a gene does, just what it does in a particular environment.
Heritability of various aspects of cognitive development is very high (e.g., around 70 percent for IQ) in kids from high–socioeconomic status (SES) families but is only around 10 percent in low-SES kids. Thus, higher SES allows the full range of genetic influences on cognition to flourish, whereas lower-SES settings restrict them. In other words, genes are nearly irrelevant to cognitive development if you’re growing up in awful poverty—poverty’s adverse effects trump the genetics.*
those that produce higher levels of synaptic dopamine (i.e., transporter variants that are less efficient) in the striatum are associated with people who are more oriented toward social signaling—they’re drawn more than average to happy faces, are more repelled by angry faces, and have more positive parenting styles.
the more gender equal the country, the less of a discrepancy in math scores. By the time you get to the Scandinavian countries, it’s statistically insignificant. And by the time you examine the most gender-equal country on earth at the time, Iceland, girls are better at math than boys.*
cross-cultural psychology studies compare collectivist with individualist cultures. This almost always means comparisons between subjects from collectivist East Asian cultures and Americans, coming from that mother of all individualist cultures.* As defined, collectivist cultures are about harmony, interdependence, conformity, and having the needs of the group guiding behavior, whereas individualist cultures are about autonomy, personal achievement, uniqueness, and the needs and rights of the individual.
individualist culture can be summarized by that classic American concept of “looking out for number one”; collectivist culture can be summarized by the archetypical experience of American Peace Corps teachers in such countries—pose your students a math question, and no one will volunteer the correct answer because they don’t want to stand out and shame their classmates.
What was the response to this insult? It depended. Subjects from the South, but not from elsewhere, showed massive increases in levels of testosterone and glucocorticoids—anger, rage, stress. Subjects were then told a scenario where a guy observes a male acquaintance making a pass at his fiancée—what happens next in the story? In control subjects, Southerners were a bit more likely than Northerners to imagine a violent outcome. And after being insulted? No change in Northerners and a massive boost in imagined violence among Southerners.
Put simply, cultures with more income inequality have less social capital.35 Trust requires reciprocity, and reciprocity requires equality, whereas hierarchy is about domination and asymmetry.
as income inequality grows, the percentage of people who bother voting generally declines.)
The more income inequality, the less likely people are to help someone (in an experimental setting) and the less generous and cooperative they are in economic games.
Poverty is not a predictor of crime as much as poverty amid plenty is. For example, extent of income inequality is a major predictor of rates of violent crime across American states and across industrialized nations.
A final depressing point about inequality and violence. As we’ve seen, a rat being shocked activates a stress response. But a rat being shocked who can then bite the hell out of another rat has less of a stress response. Likewise with baboons—if you are low ranking, a reliable way to reduce glucocorticoid secretion is to displace aggression onto those even lower in the pecking order. It’s something similar here—despite the conservative nightmare of class warfare, of the poor rising up to slaughter the wealthy, when inequality fuels violence, it is mostly the poor preying on the poor.
In the developed world, when compared with rural populations, city dwellers are typically healthier and wealthier; larger social networks facilitate innovation; because of economies of scale, cities leave a smaller per-capita ecological footprint.
larger groups evolved “third-party punishment” (stay tuned for more in the next chapter)—rather than victims punishing norm violators, punishment is meted out by objective third parties, such as police and courts. At an extreme, a crime not only victimizes its victim but also is an affront to the collective population—hence “The People Versus Joe Blow.”*
it is only when societies grow large enough that people regularly encounter strangers that “Big Gods” emerge—deities who are concerned with human morality and punish our transgressions.45 Societies with frequent anonymous interactions tend to outsource punishment to gods.* In contrast, hunter-gatherers’ gods are less likely than chance to care whether we’ve been naughty or nice.
High-density living doesn’t make rats more aggressive. Instead it makes aggressive rats more aggressive.
In contrast, crowding makes unaggressive individuals more timid. In other words, it exaggerates preexisting social tendencies.
Why does religion arise? Because it makes in-groups more cooperative and viable
some pertinent patterns amid this variation. As noted, desert cultures are prone toward monotheistic religions; rain forest dwellers, polytheistic ones. Nomadic pastoralists’ deities tend to value war and valor in battle as an entrée to a good afterlife. Agriculturalists invent gods who alter the weather.
Gossip is the weapon of norm enforcement.
The HGs who peopled earth for hundreds of thousands of years were probably no angels, being perfectly capable of murder. However, “war”—both in the sense that haunts our modern world and in the stripped-down sense that haunted our ancestors—seems to have been rare until most humans abandoned the nomadic HG lifestyle. Our history as a species has not been soaked in escalated conflict.
probably the most important fact about genetics and culture is the delayed maturation of the frontal cortex—the genetic programming for the young frontal cortex to be freer from genes than other brain regions, to be sculpted instead by environment, to sop up cultural norms.
most of earth’s humans have inherited their beliefs about the nature of birth and death and everything in between and thereafter from preliterate Middle Eastern pastoralists.
“A chicken is an egg’s way of making another egg”—behavior is just an epiphenomenon, a means of getting copies of genes into the next generation.
