To pinpoint genes that influence the shape of the human face and head, Shriver began with an online database of genes linked to disease — Online Mendelian Inheritance of Man. If the symptoms of the disease involved the face or skull the gene implicated in the disease became a candidate for those facial traits.
This approach works because although Shriver looked at genes implicated in disease, those same genes in a healthy person may also influence the same physical trait — length, width, shape, size — but within the range normal for healthy individuals. Facial traits vary among humans, but do tend to group by population. For example, in general, West Africans have wider faces than Europeans and Europeans have longer faces than West Africans.
From their DNA profiles, Shriver could determine the admixture percentages of each individual, how much of their genetic make up came from each group. He could then compare the genetically determined admixture to the facial feature differences and determine the relative differences from the parental populations.
Next time someone tells you race isn’t biological/genetic: they’re wrong.