

Decades of genetics research have shown...that people are born with different hereditary potentials for intelligence and that these genetic endowments are responsible for much of the variation in mental ability among individuals. Last spring an international team of scientists headed by Robert Plomin of the Institute of Psychiatry in London announced the discovery of the first gene linked to intelligence. Of course, genes have their effects only in interaction with environments, partly by enhancing an individual's exposure or sensitivity to formative experiences. Differences in general intelligence, whether measured as IQ or, more accurately, as g are both genetic and environmental in origin--just as are all other psychological traits and attitudes studied so far, including personality, vocational interests and societal attitudes. This is old news among the experts. The experts have, however, been startled by more recent discoveries.



One is that the heritability of IQ rises with age--that is to say, the extent to which genetics accounts for differences in IQ among individuals increases as people get older. Studies comparing identical and fraternal twins, published in the past decade by a group led by Thomas J. Bouchard, Jr., of the University of Minnesota and other scholars, show that about 40 percent of IQ differences among preschoolers stems from genetic differences but that heritability rises to 60 percent by adolescence and to 80 percent by late adulthood. With age, differences among individuals in their developed intelligence come to mirror more closely their genetic differences. It appears that the effects of environment on intelligence fade rather than grow with time. In hindsight, perhaps this should have come as no surprise. Young children have the circumstances of their lives imposed on them by parents, schools and other agents of society, but as people get older they become more independent and tend to seek out the life niches that are most congenial to their genetic proclivities.



A second big surprise for intelligence experts was the discovery that environments shared by siblings have little to do with IQ. Many people still mistakenly believe that social, psychological and economic differences among families create lasting and marked differences in IQ. Behavioral geneticists refer to such environmental effects as "shared" because they are common to siblings who grow up together. Research has shown that although shared environments do have a modest influence on IQ in childhood, their effects dissipate by adolescence. The IQs of adopted children, for example, lose all resemblance to those of their adoptive family members and become more like the IQs of the biological parents they have never known. Such findings suggest that siblings either do not share influential aspects of the rearing environment or do not experience them in the same way. Much behavioral genetics research currently focuses on the still mysterious processes by which environments make members of a household less alike. _Linda Gottfredson

Continent/Region Country Average IQ Asia 108 Asia 106 Asia 105 Europe 102 Europe 101 Asia 101 Europe 101 Europe 100 Asia 100 Europe 100 Europe 100 Europe 100 Europe 100 Europe 99 North America 99 Europe 99 Europe 99 Europe 99 Oceania 99 Europe 99 Europe 99 Europe 98 Oceania 98 Europe 98 Europe 98 Continent/Region Country Average IQ Europe 98 Europe 98 Europe 98 Europe 98 North America 98 Europe 97 Europe 97 Europe 97 Europe 97 Europe 96 Europe 96 Europe 96 South America 96 Middle East 95 Europe 95 Middle East 94 Middle East 94 Asia 94 Europe 94 Asia 94 South America 93 Europe 93 Europe 92 Europe 92 Asia 92

The general finding after over 100 years of studying intelligence and genetics, is that IQ is heritable over the lifetime to between 50% and 80%. Heritability of IQ tends to be lower in low socioeconomic groups and in very young children. As a person ages, the genes tend to influence intelligence more. The table below is a guessing game, where you are to fill in the "country" which matches the continent and the IQ score . The table of national IQs below, should assist you in this task. Notice that African nations are not included in the game, since the national IQ scores in the game do not go below 92.This graphic displays a simplified bell curve distribution overlap for 4 generalised human population groupings.This graphic provides a general idea as to realistic occupational expectations for individuals whose valid IQ scores fall within a particular range of values.This simplified time projection from the Fourmilab website: Global IQ 1950-2050 , looks at the change in average "global IQ" over time, due to differential birthrates among distinct breeding groups, possessing different IQ.Total fertility rates by country (via the EvoandProud anthropology site). By comparing the TFRs and national IQs, one can estimate the general trend for global IQ, as a falsifiable hypothesis.What about the "Flynn Effect?" Unfortunately, the multiple and poorly defined underlying mechanisms behind the "Flynn Effect" are not strong enough to overcome the compounding magic of differential birthrates combined with heritability of IQ.This graphic allows you to visually compare homicide rates with both total fertility rates and national IQ. Keeping in mind the heritability of IQ, this triple juxtaposition allows for some simple falsifiable predictions as to the future of both particular nations, and of the nations which are emigration targets for the excess from low IQ, high crime, high fertility populations.Hope for the best. Plan for the worst.More: Here is an extremely optimistic look at the future of commodities, energy resources, and food. The human ingenuity of " the smart fraction " has been pushing back against the forces of depletion -- just as Julian Simon said they would do It is crucial to look at as many sides to the story as one can. Nothing in real life is as simple as it seems.

Labels: demographic change, IQ