What does the distribution curve of IQ in the world population look like? If the average IQ for all countries is 90 (Richard Lynn and Tatu Vanhanen “IQ and the Wealth of Nations”), with an average IQ for sub-Saharan Africans of 70, I suppose that the distribution curve is higher on the downside. If the environment is equalized (relevant to IQ) and gene pools merge, I suppose that the normalized bell curve becomes reality. In the absence of catastrophes, is the evolution of intelligence then limited by IQ drift (including the Flynn effect)? Is advanced intelligence fundamentally different from other "most relevant traits" from an evolutionary point of view? Does the complexity of the trait make a disadvantageous mutation more likely?