Heritability increases from about 0.4 in childhood to 0.8 in later adulthood. The way these heritabilities are estimated is through numerous experiments on twins, adopted children, longitudinal studies, inbreeding depression research, etc. Nothing in science can be proven however. We know of gravity, but it is just a theory. We don't know what it is. So what psychometricians are claiming is that the best evidence, based on similar research around the world, from thousands of studies, indicates that intelligence is highly heritable. In addition, very little evidence has been forthcoming showing that environment has much of an impact. Some data from nutrition, pathogens or diseases, etc. but very little real impact on intelligence has been shown so far. SES also has very little impact on intelligence - numerous studies factor out the impact of SES on research results. It is quite easily controlled for. It is a matter of doing numerous types of studies that are peer reviewed, studies and assertions that can be falsified, and settling in on those theories that best fit the data. To date, it shows that intelligence or mental ability is very important, it is highly heritable, and it varies by individual and by races on average. A child inherits ONE off TWO possible chromosomes from each parent's set of 23. 2 raised to the 23 power possible combinations. Some people get lucky and inherit far more smart genes than dumb ones; the next kid in the family can get unlucky and get mostly dumb genes from the parents. These emergent properties have been known to breeders for over 10,000 years - not how it works genetically but how to breed for the best emergent properties. Now we know how it is done. Eugenics takes the lucky kids and they have more offspring than the unlucky ones, just like dog breeders do. Except breeders may cull the least fit, just as our ancestors have been known to do (see Mother Nature by Hrdy). The research on racial differences is also readily available from studying races around the world. The pattern is irrefutable and cannot be due to the environment. Average racial intelligences range from East Asians at about 106 to sub Saharan Blacks and Australian Aborigines at about 70. (See "The Scientific Study of General Intelligence" by numerous others, 2003.) The question about how we can know heritability without knowing the genes is like asking how humans could have been breeding crops and animals for 10,000 years without knowing about genes. It is sophomoric. We study gravity, and yet it is still a theory. We don't know WHAT it is. It can't be proven. Yet we are all pretty sure it is what we think it is in terms of its repeatability. That is how intelligence is studied, using quantitative genetics, numerous studies, chronometric research on brain sizes, pH, glucose uptake, myelination, etc. Intelligence has been so thoroughly triangulated by so many methodologies that the social scientists have virtually given up trying to counter Jensenism with their own research. They have taken to mostly ignoring psychometrics, rather than challenge it. They have been routed and are on the run. And as for apartheid because of racial differences, that is already the case. That is why Blacks deny intelligence testing, have moved to ban it, use quotas, etc. The tensions are already there because most people who already deal with Blacks on a day-to-day basis know they are less intelligent. Researchers note how Galton and Burt both had first hand knowledge of the less intelligent, while many elite academics do not. They can pretend that there are no real differences, because they do not rub shoulders with the underclass. It is to be noted that no research has shown that intelligence is not highly heritable. That is, the naïve environmentalist position is dead in the water - it is moribund and going nowhere. Behavior geneticists have the only game in town, so one must accept the most parsimonious explanations with regards to intelligence and racial differences, or supply some data of their own that can overturn the Jensenism. There is far more genetic variation within a breed of dog than there is between breeds. Now try taking a wolf over to a friend's house and ask if they can watch it for you for a while. Absurd of course. And yet, just a few genes determines the ferocity of a Wolf and the gentleness of Greyhound (not to mention the low IQ of Greyhounds compared to Border Collies). I believe they now have dog contests or shows that are "performance" in nature. From the couple I saw it looked to me that they were mostly Border Collies, the smartest of all breeds according to the book "The Intelligence of Dogs." So, the same rule applies to human breeds/races. Race does not determine intelligence, evolution does. Many things impact different average intelligences within closely related races. Differential migration, cultural effects on breeding patterns, etc. Intelligence varies on many fronts within races such as rural versus cosmopolitan - the smart kids head for the city. For any group, whether race or some other criteria, average intelligences are based on past breeding patterns. Studies on intelligence have been going on for over 100 years, and there is no indication that drug abuse, alcohol, or nutrition is a determinant of differences in average intelligence, of for individuals as far as that is concerned. There are damaged children from mothers, who are abusing drugs or alcohol, but they are a small minority and it occurs in every race. But also, it has nothing to do with genetics. A child could be intellectually damaged, say from a soccer head injury, but that debility is not passed onto the children. Intelligence is still primarily genetic. The naïve environmentalists have never shown that "pockets" of alcohol, drugs or nutrition can account for differences in average intelligence between races. Nutrition does have a slight effect on intelligence, but not much. Just like stature, which is 90% genetic, but without adequate nutrition people will not develop. But today, there is no indication that lack of nutrition has any impact at all. Blacks in the US develop physically quite well, have no shortage of food, and studies have shown that their nutritional needs are about the same as Whites. The difference is genetic - no other naïve environmental cause has been found to explain the differences. Richard Lynn is the leading advocate of nutrition to increase IQ, but it has at best a small impact. Why do you think that nutrition is not promoted to close the gap between Whites and Blacks? Actually, intelligence has high predictive validity with health. Intelligent people live longer, healthier lives. They understand diseases they may have, they can follow recommendations for taking medicine and following diets, etc., and they have far fewer accidents. Intelligence is the single most important determinate of numerous life outcomes, and they are all positive except for one - intelligent people live with the angst of knowing how stupid other people are. Regarding evolution, when the races split, as they are constantly doing, different ecological niches select for different phenotypes, including behavioral traits and intelligence. There is no point in our history where "an intelligence" was selected for and when to fixation. Intelligence, unlike having five fingers, is highly variable by individuals and race: Ashkenazi Jews have an average IQ of about 108~115, while sub-Saharan Africans have and average IQ of 70. Each group has continued to evolve and is still evolving. Evolution never takes a break or ceases to operate on any organism. There is no teleological goal to evolution that states 'we have arrived, let's not change on iota from this point on.' I am planning to research the databank at http://www.theoccidentalquarterly.com/ which appears to contain a large volume of scientific research on the topics of intelligence, personality, human interaction, race/ethnicity, and human evolution. If I come across any interesting data, I will post them here.