Scientists study the Neanderthal genome not just to learn about Neanderthals. As our closest extinct relative, Neanderthals help us chart the various genetic changes that led us to become human.
If you’ve ever played the game “Operator,” you know how messages can get distorted over time. The game goes like this: One person whispers to another the message “Sally sells shells by the seashore.” This person then whispers it into the next person’s ear, and so on. Invariably, someone hears the message wrong and makes a mistake: “Shall we sell shells by the seashore.” After a string of transmissions, the message has turned into something like, “Shall we gals sell the flea store.”
Transmission of genetic information from generation to generation is a little like a game of Operator. Each time genetic information is passed from one generation to the next, there’s a chance that a variation—a mutation—may arise. As long as the mutation “makes sense,” that is, if it doesn’t do serious damage to the creature’s form or function, it will get passed along to the next generation.
The slow morphing of a genome over time, called genetic drift, can ultimately lead to entirely new species. To understand how, just imagine two games of Operator being played simultaneously by two different groups. Both groups begin with the same sentence, but gradually the message morphs into two entirely different messages. The longer the game runs, the more different the two messages end up—one becoming, for example, “Silly bells tell them be sore,” while the other becomes “They still fell by the report.”
Just as these two sentences gradually diverged from one, humans and chimpanzees gradually diverged from a single common species that existed roughly 5 million years ago. Comparing the human genome with the chimpanzee genome has allowed us to see exactly which changes occurred during those 5 million years.
With new information about the Neanderthal genome, we can make further, finer comparisons. Humans and Neanderthals also once shared a common ancestor, but our split with the Neanderthals is much more recent, less than a million years ago. If we’d been playing a game of Operator, comparing modern human DNA with Neanderthal DNA would be like rewinding the game a few steps to see which changes happened most recently. It’s these recent changes that make our species so unique—unique enough to think up games like Operator.