Yes, we are still evolving

Nicholas Wade reports in the NYT of research that demonstrates that we are still evolving. This is not really news. We know that tooth size has dropped an average of 11% since the neolithic period. I am curious to know why the authors have singled out only selection for these traits and not drift coupled with selection, since selection will act more quickly on smaller populations where drift has occured and more slowly on larger populations where there is little drift.