Over recent decades, psychologists have converged on a model of personality sometimes called the Big Five Factors Plus IQ. As Geoffrey Miller points out in Spent, this is not some revelation that a charismatic genius like Freud has brought down from the mountaintop. Instead, it's an emergent consensus of a whole bunch of researchers.
Conscientiousness is becoming popular as the Big Five factor that's most like IQ in that it's broadly applicable. Just as all else being equal, in hiring for almost any job you'd rather have somebody with more rather than less IQ, you'd like to have somebody with more rather than less conscientiousness.
Bruce G. Charlton has an interesting essay on IQ and Conscientiousness that begins:
The psychological attributes of intelligence and personality are usually seen as being quite distinct in nature: higher intelligence being regarded a â€?giftâ€™ (bestowed mostly by heredity); while personality or â€?characterâ€™ is morally evaluated by others, on the assumption that it is mostly a consequence of choice? So a teacher is more likely to praise a child for their highly Conscientious personality (high â€?Câ€™) â€“ an ability to take the long view, work hard with self-discipline and persevere in the face of difficulty â€“ than for possessing high IQ. Even in science, where high intelligence is greatly valued, it is seen as being more virtuous to be a reliable and steady worker. Yet it is probable that both IQ and personality traits (such as high-C) are about-equally inherited â€?giftsâ€™ (heritability of both likely to be in excess of 0.5). Rankings of both IQ and C are generally stable throughout life (although absolute levels of both will typically increase throughout the lifespan, with IQ peaking in late-teens and C probably peaking in middle age). Furthermore, high IQ is not just an ability to be used only as required; higher IQ also carries various behavioural predispositions â€“ as reflected in the positive correlation with the personality trait of Openness to Experience; and characteristically â€?left-wingâ€™ or â€?enlightenedâ€™ socio-political values among high IQ individuals. However, IQ is â€?effortlessâ€™ while high-C emerges mainly in tough situations where exceptional effort is required. So we probably tend to regard personality in moral terms because this fits with a social system that provides incentives for virtuous behaviour (including Conscientiousness).
Yet, it would seem like Conscientiousness is historically alterable — e.g., the Victorian English seem a lot more conscientiousness than their Regency grandparents, while today's English seem like bigger screw-offs than their grandparents.