The evolution of conscientiousness

For most of Geoffrey Miller’s Spent: Sex, Evolution, and Consumer Behavior (earlier posts here and here), Miller treats the genetic influences on human preferences as relatively static over human history. However, in his discussion of the big-five personality trait of conscientiousness, Miller suggests that high conscientiousness was only selected for after the Neolithic Revolution:

In several respects, conscientiousness is an unusual personality trait. Because hunter-gatherer life did not require as much planning and memory for debts and duties as life in larger-scale societies with more complex divisions of labor, conscientiousness may have evolved to higher average levels only recently, and perhaps to a greater degree in some populations than others. Only with the rise of activities like agriculture and animal herding would our ancestors have needed the sort of anxious obsessiveness and future-mindedness that characterize the highly conscientious. Only in the past ten thousand years did our ancestors prosper by continually asking themselves: Have I plowed enough yet? Did I sow the seeds early enough? Is one of the lambs missing? Did my cousin pay me for those olives? Am I teaching my children the skills they will need in twenty years? Thus were born the sleepless predawn ruminations of the middle-aged conscientious.

Economically, conscientiousness is a positive trait (both individually and in the aggregate). While I would argue that other traits would have also faced selection pressures since the Neolithic Revolution, it is probably easier to build a case for conscientiousness evolving in an economically useful manner than for the other big-five traits.

Miller couched most of his discussion in Spent in terms of the big-five (openness, conscientiousness, agreeableness, stability and extraversion) plus general intelligence (the central six as he calls them). Rob Brooks did similarly in Sex, Genes & Rock ‘n’ Roll. It’s probably not a bad habit to get into, as Miller suggests most of the studies about the heritability of preferences (such as in my recent post on the heritability of political views) are simply reflections of the central-six. In their favour, the central-six are near statistically independent, apart from a slight correlation between openness and intelligence, and have survived in various forms through several decades of psychological research.

As for the trait I often talk about, time preference or patience, I expect that this is a combination of intelligence and conscientiousness.

8 comments

  1. There were at least four neolithic revolutions occurring in widely differing climates and at widely differing times. Did each of them enhance conscientiousness? To the same degree?

    1. I would say yes to the first but no to the second. I am sure there are exceptions, but I’d expect lower selection for conscientiousness as you move towards the equator and seasons are less variable (I recently listened to a podcast in which Philip Zimbardo touched on differing time orientations on this basis). The nature of the crop – annual or perennial – would also be relevant. In addition, one thing that always strikes me when I read about the cultivation of rice is how much hard work is involved – from the tight rotations, transplantation of seedlings and general labour intensity.

    1. This seems to be a question of parsimony versus predictive power. Given the weak correlation (accepting the estimates used by Rushton and Irwing) between the big-five, you lose predictive power by putting them into a single index. I find the different categories useful and I’d expect differing selective forces on them – how did agriculture affect openness? Or agreeableness? Which is more important economically? As to why I don’t want to break them down further – that’s parsimony kicking in.

      While like the idea of using the central-six as a framing tool, if someone comes up with a convincing and statistically robust alternative breakdown, I’m open to be convinced. I think Miller sums it up well:

      General intelligence is unlikely to be dethroned as the queen of predictive power in the land of psychodiversity, but the Big Five might be replaced with an even better model of personality variation at some future point. This will depend on new discoveries in genetics (do the Big Five depend on distinct sets of genes?), neuroscience (do the Big Five depend on distinct brain systems?), and evolutionary psychology (do the Big Five serve distinct adaptive functions?). We need a much clearer idea of why evolution should have maintained heritable variation in five main personality traits, rather than three, or eight, or fifty. The answer must have something to do with the number of ways that human social strategies could vary adaptively within prehistoric clans. Several researchers are working hard on this issue in the new field of evolutionary personality psychology. But for the moment, the Big Five is the best model we have, and we might as well see how far we can go with it.

  2. This analysis is essentially a rehash of the farmer v. hunter theory of ADHD, which quite possibly is simply a subset of individuals with low conscientiousness.

    Honestly, I’m skeptical of this kind of “just so story” approach. It isn’t hard to imagine conscientiousness haven’t relevance is rather primative settings — for example, there is considerable need for precision custom tool making in matters like tying spearpoints to spears and making bows and arrows, that go into hunting and war making. Is there anyone more anxiously obssessive than a soldier getting ready for battle? And, in a pre-literate society, meticulous attention to who owes what to whom can be more relevant especially when it comes to maintaining peace with neighboring bands.

    Also, there has been a fair amount of suggestion that the genetic structure of personality is quite different than that for IQ. There is widespread suspicion that IQ is the sum of lots of little positively selected pieces that people have in greater or less degrees. In contrast, there is suspicion that big five personality traits, which are largely independent of IQ even in very extreme IQ ranges, is a trait for which the most adaptive outcome for a society is to have a mix of indiviudals, and for which a fairly small set of genes that have not and are not headed towards fixation in the population may account for each one.

    This doesn’t mean that there couldn’t be different mixed of genes related to personality traits in different populations, but one would want to be exceedingly cautious in distinguishing between gene mixes and gene expression in this area. Some of the initial research I’ve seen in this area, for example showing high levels of genes associated with impulsivity and novelty seeking in stereotypically uptight Japan, suggests that one can’t take anything for granted in this analysis.

  3. “As for the trait I often talk about, time preference or patience, I
    expect that this is a combination of intelligence and conscientiousness.”
    You say more in fewer words than any blog i know. I wish all blogs were so concise (& so accurate). Well-done!

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