Placing intelligence into an evolutionary framework or how g fits into the r–K matrix of life-history traits including longevity
J P Rushton; 2004
First, I describe why intelligence (Spearman’s g) can only be fully understood through r–K theory, which places it into an evolutionary framework along with brain size, longevity, maturation speed, and several other life-history traits. The r–K formulation explains why IQ predicts longevity and also why the gap in mortality rates between rich and poor has increased with greater access to health care. Next, I illustrate the power of this approach by analyzing a large data set of life-history variables on 234 mammalian species and find that brain size correlates r=.70 with longevity (.59, after controlling for body weight and body length). A principal component analysis reveals a single r–K life-history factor with loadings such as: brain weight (.85), longevity (.91), gestation time (.86), birth weight (.62), litter size ( .54), age at first mating (.73), duration of lactation (.67), body weight (.61), and body length (.63). The factor loadings remain high when body weight and length are covaried. Finally, I demonstrate the theoretical importance of this approach in restoring the concept of bprogressQ to its proper place in evolutionary biology showing why, over the last 575 million years of evolutionary competition of finding and filling new niches, there has always been (and likely always will be) broom at the top.