A new theory suggests that more intelligent people are more likely than less intelligent people to adopt evolutionarily novel preferences and values, and that these values include liberalism (caring about numerous genetically unrelated strangers they never meet or interact with), atheism, and, in men, monogamy. Data from the National Longitudinal Study of Adolescent Health (Add Health) provide support: Young adults who self-identify as "very liberal" have an average IQ of 106 while those who self-identify as "very conservative" have an average IQ of 95; young adults who self-identify as "not at all religious" have an average IQ of 103, while those who self-identify as "very religious" have an average IQ of 97. The study follows on from a previous study showing that more intelligent individuals were more nocturnal, waking up and staying up later than less intelligent individuals. Being nocturnal is evolutionarily novel for humans.

A new analysis of data first published in 2002 in a controversial book called IQ and the Wealth of Nations and then expanded in 2006, argues that national differences in IQ are best explained not by differences in national wealth (the original researchers’ explanation), but by the toll of infectious diseases. The idea is that energy used to fight infection is energy taken from brain development in children. Using 2004 data on infectious disease burden from the World Health Organization, and factors that have been linked to national IQ, such as nutrition, literacy, education, gross domestic product, and temperature, the analysis revealed that infectious disease burden was more closely correlated to average IQ than the other variables, alone accounting for 67% of the worldwide variation in intelligence. The researchers also suggest that the Flynn effect (the rise in IQs seen in developed countries during the 20th century) may be caused in part by the decrease in the intensity of infectious diseases as nations develop.

A study involving 136 healthy institutionalized infants (average age 21 months) from six orphanages in Bucharest, Romania, has found that those randomly assigned to a foster care program showed rapid increases in height and weight (but not head circumference), so that by 12 months, all of them were in the normal range for height, 90% were in the normal range for weight, and 94% were in the normal range of weight for height. Caregiving quality (particularly sensitivity and positive regard for the child, including physical affection) positively correlated with catch-up. Children whose height caught up to normal levels also appeared to improve their cognitive abilities. Each incremental increase of one in standardized height scores between baseline and 42 months was associated with an average increase of 12.6 points in verbal IQ.