Flynn has a paper in press which makes, once again, the Flynn effect to the rescue case:
Table 5c gives Raven’s trends from the developing world. Kenya and Dominica appear to have embarked on a period of explosive gains. Sudan has made gains on the WAIS: large fluid gains (on the Performance Scale) were accompanied by a small loss for crystallized intelligence (Daley, Whaley, Sigman, Espinosa, & Neumann, 2003; Khaleefa, Sulman, & Lynn, 2009; Meisenberg, Lawless, Lambert, & Newton, 2005). Flynn (2009c) speculates that the developing world in general may soon experience the Scandinavian decline. If that occurs, and if developing nations are entering a long period of peak gains, the 21st century will see the IQ gap between those two worlds close. (Flynn and Rossi-Casé, 2012. IQ gains in Argentina between 1964 and 1998.)
What’s uncanny, from this perspective, is the decade to decade constancy of the international differences in FSIQ. The table below, for example, lists all the studies published to date with respect to North Africa (Al-Shahomee (2012), excepting). Over the last 50 years, there has been little change in the UK/Europe-North African gap. Similar results are found for the UK/Europe-African gap and others. Flynn’s argument is that the secular increase will slow in developed countries and speed up in developing countries, leading to a complete convergence. By this same logic, one might have expected a large divergence between developed and developing countries over the last century. The quality of life/education, etc., gaps, after all, have not remained constant. For example, in the case of Sudan, in the last half of the last century, the WAIS IQs increased at 2.05 points per decade as compared to the 3 points per decade in the US, while, over the same period, Per capita income has increased almost 200% more in the US. Were per capita income behind the secular rise, we would expect a large divergence between US and Sudan scores.
Whatever the case, Flynn’s argument seems plausible. Which is why intra-national IQ differences — or the possible lack thereof – are the important ones when it comes to determining the plausibility of a genetic hypothesis.