Lynn and Vanhanen spotlighted the relationship between IQ and the purchasing power parity of nations. It was a groundbreaking new way of understanding prosperity in the world. But PPP's relationship with IQ (contemporary correlation of .60) is actually weak in comparison to IQ's relationship to a host of other quantifiables (Economic transparency/corruption index: .68, Distance from the equator: .67, Births per woman: -.81, Life expectancy: .85). When economic transparency/corruption is taken into account, the effect of IQ on PPP completely disappears, while controlling for a host of variables (IQ, distance from the equator, births per woman, net migration rate, life expectancy, and economic freedom) only mildly moderates the effect of economic transparency/corruption while rendering all the other variables statistically insignificant except for the migration rate (positive net migration being correlated with higher PPP).
Another surprisingly strong correlation exists between IQ and the infant mortality rate. The two are inversely correlated at a statistically significant .84. Thus 70% of a country's infant mortatlity rate can be 'explained' by its average IQ. By way of comparison, PPP and infant mortality are inversely correlated at a more modest .56. Even doctors per capita and infant mortality are only inversely correlated at .69. Controlling for IQ renders PPP meaningless. Doctors per capita retains statistically significant but loses two-thirds of its correlation magnitude. Controlling for PPP and doctors per capita, meanwhile, only cuts into 21% of IQ's 'effect' on infant mortality. Boosting African IQs through better nutrition will do more for the well-being of the continent than the noble Doctors without Borders organization will ever be able to accomplish (maybe they should focus on distributing vitamins).
Why does IQ matter more than access to physicians or material well-being? There's plenty of food for speculation: Smarter women have more self-control to refrain from activities during pregnancy that may damage the fetus like smoking, eating junkfood, and consuming alcohol, they have fewer kids and have them later in life so they can devote more attention to each child without the distractions of youth, sharper couples are less likely to get divorced and therefore children benefit from having two caretakers instead of one, brighter couples have brighter children that are less likely to accidentally kill themselves, and smarter people are less given to instant gratification that distracts from properly caring for infants.
The future looks precarious. The brainy nations are becoming grayer and reproducing below the replenishment rate of 2.1 children per woman (see the nearby charts--click to enlarge).
Globalization will continue to make migration easier. As newly-arrived, formerly destitute third-worlders enjoy the prosperity of the developed host, they become more fecund (Hispanics in the US average 2.8 babies per woman. That's higher than Mexico's 2.42 per woman, and indeed is more fertile than much of Latin America). By depressing wages and making housing less affordable, they also have the effect of decreasing the fecundity of the host country's natives. As the relative size of the smart fraction dwindles while the duller side grows proportionately (and absolutely, of course), more human resources will have to spent by the brights to take care of the dulls. Crime and poverty will increase, living standards will be pressured, and human progression will be slowed.
Three ways to combat this: 1) Genetic engineering, the azoth that will potentially make all this worrying silly, 2) Technologies and techniques to slow down the aging process, keeping erudite old folks productive longer (SENS research is a worthy cause for charitable contributions), and 3) The creation of incentives for natives of the developed world to have more babies. France, Russia, and Portugal have recently implemented policies in attempt to achieve this. The US should give tax credits to high IQ professionals for donating sperm and eggs. The child tax credit should be regressive, or at least not progressive. Tubal ligations and other forms of sterilization should be used more by prosecutors as part of plea deals for criminals (Project Prevention is another worthy cause to consider).