After years of writing about human evolution, I decided recently to find out about my own ancestry. So I bought a DNA spit kit for $299 from 23andMe, a personalized genomics company in Mountain View, Calif. After spitting repeatedly into a plastic tube, I mailed my sample to a lab in California where technicians extracted DNA from cheek cells in my saliva. Two weeks later, I got an email with the subject line “Your 23andMe results are ready!”

I quickly logged in and clicked on a heading called My Ancestry. I found pretty much what I expected: I’m 100 percent European, albeit descended from an ancient group that once lived in a place that no longer exists—Doggerland, now flooded by the North Sea. But much to my surprise, I also learned there was a Neanderthal in my family tree.

A box on my ancestry page said: “You have an estimated 2.9 percent Neanderthal DNA, which puts you in the 89th percentile among Northern European 23andMe members.” I immediately compared genetic notes with my husband, who suggested I declare my Neanderthal heritage as a potential conflict of interest when I write about Neanderthals (so noted). That was probably just sour grapes because he found out he has less Neanderthal DNA than I do—just 2.6 percent of his genome.