Marcia and Millie Biggs say they’ve never been subjected to racism—just curiosity and surprise that twins could have such different skin colors.

@ NationalGeographic.com, part of their special issue on race for April, 2018; this excerpt by Patricia Emmons:

[....] In genetic terms, skin color “is not a binary trait” with only two possibilities, Martin notes. “It’s a quantitative trait, and everyone has some gradient on this spectrum.”

Historically, when humans have drawn lines of identity—separating Us from Them—they’ve often relied on skin color as a proxy for race. But the 21st-century understanding of human genetics tells us that the whole idea of race is a human invention.

Modern science confirms “that the visible differences between peoples are accidents of history”—the result of mutations, migrations, natural selection, the isolation of some populations, and interbreeding among others, writes science journalist Elizabeth Kolbert. They are not racial differences because the very concept of race—to quote DNA-sequencing pioneer Craig Venter—“has no genetic or scientific basis.”

And yet 50 years after the assassination of Rev. Martin Luther King, Jr., racial identity has reemerged as a fundamental dividing line in our world.

We’re devoting the April issue of National Geographic to the complicated issue of race.

The Race Issue includes a story about how scientific ideas of race originated, a letter from our editor exploring National Geographic’s own checkered history on race, and a video-driven feature documenting the phenomenon of black men getting stopped by police while driving.

This month’s issue is just a starting point. We’re doing stories on the evolving identities of key ethnic, religious, and racial groups throughout 2018.