 In response, an international group of 23 scientists published a letter in "Times Higher Education" defending Kanazawa's work.In 2006, Kanazawa used the "Savanna principle" to explain the correlation of health and IQ vs. health and wealth.He argued that IQ is a better predictor for health than wealth or inequality in most regions of the world, except in Sub-Saharan Africa, where health is more strongly correlated to wealth than to IQ, because Sub-Saharan Africa represents an "evolutionary familiar" environment with lesser selection pressure on IQ than elsewhere.