For most of Geoffrey Miller’s Spent: Sex, Evolution, and Consumer Behavior
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.