Comparing neutral markers, selective markers and human cranial morphology: are human skulls neutral?

Abstract

The microevolutionary processes involved in the evolution of the human skull are researched in many different ways. Recent studies compared the biological distances obtained for human skulls and microsatellites, attempting to test the correlation between them. Two of these studies found a positive and significant correlation between morphology and neutral molecular markers and concluded that the evolution of human skull as a whole followed stochastic events such as genetic drift and gene flow. Following this line of thought we compared the biological distances of genes known to be under positive selection with microsatellites and with craniometrics to investigate if the morphology still obeys a neutral pattern. To accomplish the test we used ten populations representative of Africa, Europe, Asia and Oceania that had molecular and craniometric data available for the same populations. We constructed distances matrices for all the variables and then calculated the correlation and significance between them. The results obtained were significant and positive between morphology and microsatellite (r=0.7556 p=0.001) between morphology and two selective genes (LARGE r=0.6155 p=0.001 and EDAR r=0.3259 p=0.042) and also between three selective genes and microsatellites (TYRP1 r=0.0478 p=0.042, SLC19A2 r=0.3108 p=0.042, LARGE r=0.5720 p=0.003). These results showed that it is possible to obtain positive correlations between features under selection and neutral molecular markers possibly because of the shared demographic history and that this correlation is not always synonymous of an exclusively neutral pattern of evolution.