When you look in the mirror, you’re not just looking at you—you’re looking at a whole mess of face mites. Yeah, you’ve got ‘em. Guaranteed. The little arachnids have a fondness for your skin, shoving their tubular bodies down your hair follicles, feeding on things like oil or skin cells or even bacteria. The good news is, they don’t do you any harm. The better news is, they've got fascinating secrets to tell about your ancestry.

New research out today in the Proceedings of the National Academy of Sciences reveals four distinct lineages of the face mite Demodex folliculorum that correspond to different regions of the world. African faces have genetically distinct African mites, Asian faces have Asian mites, and so too do Europeans and Latin Americans have their own varieties. Even if your family moved to a different continent long ago, your forebears passed down their brand of mites to their children, who themselves passed them on down the line.

Looking even farther back, the research also hints at how face mites hitchhiked on early humans out of Africa, evolving along with them into lineages specialized for certain groups of people around the planet. It seems we’ve had face mites for a long, long while, passing them back and forth between our family members and love-ahs with a kiss—and a little bit of face-to-face skin contact.

Leading the research was entomologist Michelle Trautwein of the California Academy of Sciences, who with her colleagues scraped people’s faces—hey, there are worse ways to make a living—then analyzed the DNA of all the mites they’d gathered. “We found four major lineages,” says Trautwein, “and the first three lineages were restricted to people of African, Asian, and Latin American ancestry.”

California Academy of Sciences

The fourth lineage, the European variety, is a bit different. It’s not restricted—it shows up in the three other groups of peoples. But Europeans tend to have only European mites, not picking up the mites of African, Asian, or Latin American folks. (It should be noted that the study didn’t delve into the face mites of all the world’s peoples. The researchers didn’t test populations like Aboriginal Australians, for instance, so there may be still more lineages beyond the four.)

So what’s going on here? Well, ever since Homo sapiens radiated out of Africa, those four groups of people have evolved in their isolation in obvious ways, like developing darker or lighter skin color. But more subtly, all manner of microorganisms have evolved right alongside humans. And with different skin types come different environments for tiny critters like mites.

“Some [skin types] do show different levels of hydration, and different levels of oil production, and different density of glands,” Trautwein says. “All kinds of differences.” So African mites may have evolved with uniquely African skin, while on the other side of the globe Latin American mites evolved with Latin American skin. As for those European mites, which show up on faces around the world, their spread is probably a side effect of imperialism and globalization. When Europeans occupied new countries, from Brazil to the Philippines, they brought along their face mites.

The populations of different lineages on our skin, though, are by no means static. Kiss your grandma on the cheek and you could exchange mites. “If you do have multiple people in your family that you spend a lot of time being physically close to, if you have multiple romantic partners across your life, there's all these different opportunities to be colonized,” says Trautwein. Because families tend to be more kissy with each other than strangers, their blends of mites may persist for generations. But it's always a give and take, mites coming and going, as cheeks hit cheeks.

Out of Africa

Any self-respecting paleoanthropologist will tell you that Homo sapiens got their start in Africa, then exploded across the globe. Wherever humans settled, they evolved differently to fit their environment. So too did their face mites. And while scientists can’t go and sequence the DNA from a face mite attached to an early human, they’ve got a trick for figuring out how these organisms’ genes have changed over expanses of evolutionary time.

USDA

The raw fuel of evolution is the mutation, which bestows an organism with a characteristic that’s either positive, neutral, or negative in regards to surviving and passing down its genes (a slightly different coloration, for example, that helps it better blend in with its surroundings). And these mutations tend to crop up at a certain rate as a species reproduces. “Because we have some understanding about how frequently DNA changes over time, how many mutations occur over time,” says Trautwein, “we can add a molecular clock to that and put a date on how long it's taken for these changes to emerge.”

Comparing the DNA of the four lineages of face mite, the researchers determined that the varieties started diverging from each other between 2.4 million and 3.8 million years ago, right around the same time that our genus Homo was coming up in the world. And among the lineages, the African and Asia brands appear to be the oldest, in keeping with the idea that humans first evolved in Africa, then moved into Asia and onwards.

“It's certainly not that we acquired these mites in the last 10,000 years, or that we got them from domesticated animals or anything like that,” Trautwein says. “It seems like these are really old splits, which means that these mites have been living with humans for all of our history, if not before.”

As humans evolved into the plethora of peoples we know today, the mites evolved along with us as our little facial companions. “The fact that they're evolving on our face brings home this idea that evolution isn't this distant thing that happened in the past, or that's happening out there to something else,” Trautwein says. “But it's happening right here under our noses.”