From the article:
DNA is often compared to a text, with the letters standing for chemical bases—A for adenine, C for cytosine, G for guanine, and T for thymine. The human genome consists of three billion base pairs—page after page of A’s, C’s, G’s, and T’s—divided into roughly 20,000 genes. The tweak that gives East Asians thicker hair is a single base change in a single gene, from a T to a C.
Similarly, the mutation that’s most responsible for giving Europeans lighter skin is a single tweak in a gene known as SLC24A5, which consists of roughly 20,000 base pairs. In one position, where most sub-Saharan Africans have a G, Europeans have an A. About a decade ago a pathologist and geneticist named Keith Cheng, at Penn State College of Medicine, discovered the mutation by studying zebrafish that had been bred to have lighter stripes. The fish, it turned out, possessed a mutation in a pigment gene analogous to the one that is mutated in Europeans.
Studying DNA extracted from ancient bones, paleogeneticists have found that the G-to-A substitution was introduced into western Europe relatively recently—about 8,000 years ago—by people migrating from the Middle East, who also brought a newfangled technology: farming. That means the people already in Europe—hunter-gatherers who created the spectacular cave paintings at Lascaux, for example—probably were not white but brown. The ancient DNA suggests that many of those dark-skinned Europeans also had blue eyes, a combination rarely seen today.
Wow! One gene has some 20K base pairs, and of those 20K changing one half of one base pair changes the quantity of melanin a person's body produces, resulting in their skin being pale or not-pale. That one tweak is what caused millennia's worth of acrimony! In-f*cking-credible! Most discomfiting, however, is that there will be gainsayers of the findings.
Mockingbirds don’t do one thing but make music for us to enjoy. They don’t eat up people’s gardens, don’t nest in corncribs, they don’t do one thing but sing their hearts out for us. That’s why it’s a sin to kill a mockingbird.
-- Harper Lee, To Kill a Mockingbird
