Science ( IF 41.845 ) Pub Date : 2020-07-31 , DOI: 10.1126/science.369.6503.491 Ann Gibbons
Humans suffer from a long list of deadly diseases—including typhoid fever, cholera, measles, smallpox, and more—that don't afflict apes and most other mammals. All of those pathogens follow the same well-trodden pathway to break into our cells: They manipulate sugar molecules called sialic acids. Hundreds of millions of these sugars stud the outer surface of every cell in the human body—and the sialic acids in humans are different from those in apes. Researchers have now traced how evolution may have scrambled to construct new defenses after that molecular vulnerability emerged in our distant ancestors. By analyzing modern human genomes and ancient DNA from our extinct cousins, the Neanderthals and Denisovans, the researchers detected a burst of evolution in our immune cells that occurred in an ancestor of all three types of humans by at least 600,000 years ago. These genetic changes may have sharpened the body's defenses against the pathogens that evolved to exploit sialic acids—but created new vulnerabilities. The evolutionary saga is a vivid illustration of the competition between humans and microbes.