The team of scientists wasn’t looking for evidence of human sexual behavior many years ago. They were studying the purpose of a particular protein, MUC7, when they discovered that one group of people, living in Sub-Saharan Africa had a version of the related gene that looked very different from the gene in other populations.
The team was using a set of 2,500 genes from modern humans to study MUC7, which helps give spit its particular consistency. In a subset of people, though, the gene that codes for MUC7 was more similar to the analogous gene in Neanderthal and Denisovan DNA, the team reports in Molecular Biology and Evolution.
The scientists believe this gene variant was introduced through “archaic introgression”—some ancient human having sex with some ancient human subspecies, whose identity is now lost.
That pairing would have occurred about 150,000 years ago, long after the two subspecies of human had split off from each other. But evidence that it happened is still hiding in our genes and adds more evidence that long ago, when there will still many types of hominins on earth, being a member of Homo sapiens wasn’t as simple or as unique as we once thought.