Mite-y DNA Helps Trace Human Migration

SCIENCE

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Discussion Ideas

The new scientific research studied populations of face mites. What are mites?
- Mites are microscopic arthropods. Arthropods are invertebrate animals that have an exoskeleton, a segmented body, and jointed appendages. Insects, arachnids (spiders), myriapods (centipedes), and crustaceans are all fellow arthropods—big brothers to miniature mites.
- The species of mite studied, Demodex folliculorum, is especially tiny, even by mite standards—about .1 millimeter (.004 inches). D. folliculorum is a mostly transparent, worm-like creature with claws and scales. (Demodex means “worm that bores into fat.”)

What do mites have to do with people?
- Face mites live on your face. Yes, your face. Everyone has them. D. folliculorum is mostly found in human hair follicles around the nose, eyebrows, forehead, and eyelashes.
  - What do they do? During the day, face mites feed on dead skin cells in and around your hair follicles. At night, face mites mate and lay eggs. On your face.
  - What don’t they do? Defecate. Face mites don’t have anuses. At the end of their short, 15-day lifespan, they simply disintegrate and their waste is released. On your face.
- Want more? Here’s Nat Geo blogger Ed Yong (also the author of the Atlantic article) telling you “[e]verything you never wanted to know about the mites that eat, crawl, and … on your face.”

OK, gross. Are face mites hurting me?
- No. Face mites are not harmful. They have a commensal relationship with their human hosts: The mite benefits, the human isn’t really impacted one way or another. We are gracious hosts.
- There is a correlation between unusual blooms of face mites and skin diseases such as rosacea, but there is no definite causation. (In dogs, Demodex blooms can trigger a potentially fatal condition called demodectic mange.)

How are face mites helping scientists trace ancient human migration patterns?
- By studying the mitochondria of face mites, researchers were able to distinguish four “clades,” or distinct groups of mite DNA. According to Science, “all four groups predate modern humans and our two species have evolved in tandem. A wealth of fossil and human genetic evidence suggests that modern humans first evolved in Africa and the distribution of mite species supports that hypothesis. Though it was the least sampled geographic area, people of African descent had the most diverse mites, possessing all four clades. From there, the authors theorize that people (carrying their mites) spread out to the other geographic regions and that, along the way, certain groups of the mites didn’t make it.”

So, people who live in different parts of the world have different “microbiomes”—how is that surprising?
- These are not people who live in different parts of the world! All the test subjects were Americans with different ancestries.
  - “‘The common sense idea would be that an African-American who had been here for generations would have picked up mites from people of European ancestry,’ says the study’s lead author. That wasn’t the case. Instead, ‘some of these people are maintaining mites for generations outside of their region of ancestry,’ says another scientist. Her team even sampled one volunteer who was born in Asia and had moved to the U.S. eight years before—and his face was full of the Group B mites that are common in Asia. One of the scientists who worked on the study says mites ‘aren’t just bugs on our faces, they are storytellers. Mites tell us about our own ancient history—it’s a complex story, and we’ve only just scratched the surface.’”

TEACHERS’ TOOLKIT

Your Wild Life: Meet Your Mites

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