For my new “Matter” column in the New York Times, I look at the latest advance in our understanding of Neanderthal DNA. Neanderthals and humans interbred about 40,000 years ago, and their DNA is still in human genomes today. Scientists are mapping those Neanderthal genes we carry, and figuring out which ones have benefited us and which have made us sick.

One thing I didn’t have room to discuss is a question that I keep asking and to which scientists always respond with intriguingly noncommittal answers: Are Neanderthals members of our own species? Are they Homo sapiens? Are they a subspecies–Homo sapiens neanderthalensis? Or are they a separate species–Homo neanderthalensis?

For much of the 1900s, many scientists saw Neanderthals