The question of cognitive differences between human populations is one of the most contentious issues in the study of human diversity. After reviewing the worldwide patterns of cognitive test performance, this article evaluates alternative causal hypotheses and evolutionary mechanisms. Racial affiliation and latitude correlate with IQ test performance, as does economic development. Religion, a history of colonialism, and a history of Communist rule are important in some cases. This article proposes mechanisms of gene-culture co-evolution that can explain the worldwide patterns. The genetic component of these mechanisms is likely to become testable with further advances in molecular genetics.
A long but very interesting publication from 2003. Some of the most interesting snippets from this pdf are..
Also the argument that the 100,000 years or so since the dispersal out of Africa were insufficient for the evolution of genetic differences is invalid. To create an IQ difference of, say, 15 points between two populations in 100,000 years, natural selection would have to drive their IQs apart by only 0.004 points every generation – about 1% of the selective pressure in late 20th-century America.
Genes, like drugs, have many side effects. This is called pleiotropy. For example, the average IQ of nearsighted people is 6 to 8 points higher than the average for normal-sighted people.
In the late 20th century United States, unequal reproductive rates favoring the less intelligent would have lowered the IQ of the population by anywhere between 0.35 and 0.8 points per generation had the environment remained unchanged over time (Loehlin, 1997; Retherford and Sewell, 1988; Vining, 1995; Lynn, 1996 – Dysgenics, Praeger).
Rushton emphasizes the need for close family ties and high parental investment in harsh climates. While most childhood mortality in the tropics was caused by uncontrollable endemic diseases, most childhood mortality in the arctic was due to the predictable challenges of seasonal food shortages and the rigors of the climate. These challenges demanded intelligent planning in addition to stable families (Rushton, 1995).
Referring to the last quote: smaller head size (easier birthing) and a faster/more prolific reproductive cycle are more important than being smart when the major cause of death in children is unpreventable diseases This could be one reason that Africans have a much higher twinning rate, and why peoples from the tropics have a gestation period about one week shorter than north east Asians or Northern Europeans. Also nice to find a source for the nearsightedness and IQ relation (I’m blind as a bat without my specs).
I’d also like to point out that for the IQ between populations to be the same, evolution of the human brain would have had to effectively stopped cold about 130,000 years ago: before the African and non-African populations separated. Since it has been shown by Bruce Lahn and others that certain brain affecting mutations have arisen in the last 37,000 years and that they vary wildly in distribution (the MCPH1 gene for example, which affects brain size) this is demonstrably not the case.
The whole paper is worth a read if you have an interest in the subject of race and IQ.