point your elbow to the ceiling.
Then imagine yourself naked.
Then look at the patch of skin on the inside of your upper arm, the part of you that almost never sees the sun.
Whatever color you see there is what experts call your basic skin color, according to professor Nina Jablonski, head of the Penn State Department of Anthropology.
This map shows skin colors across the globe - the average colors that indigenous people would see if they did the upper arm test:
Humans tend to evolve towards lighter skin when they move toward the poles, and towards darker skin when they move towards the equator. Obviously, the process takes many generations - but apparently not as many generations as once thought:
Skin has changed color in human lineages much faster than scientists had previously supposed, even without intermarriage, Jablonski says. Recent developments in comparative genomics allow scientists to sample the DNA in modern humans.
By creating genetic "clocks," scientists can make fairly careful guesses about when particular groups became the color they are today. And with the help of paleontologists and anthropologists, scientists can go further: They can wind the clock back and see what colors these populations were going back tens of thousands of years, says Jablonski.
She says that for many families on the planet, if we look back only 100 or 200 generations (that's as few as 2,500 years), "almost all of us were in a different place and we had a different color."
That's kind of amazing. That's like going from black to white in the time between Socrates and ourselves. Evolutionarily? That's really fast. (It's interesting that every new finding about human evolutionary change seems to point towards it occurring faster than previously thought.)
Here's the link to the audio of the NPR story. Thanks to loyal reader camella and&also& kt for the tip.