Researchers from the University of California's San Diego School of Medicine have found that gonorrhea, as unpleasant as it is, might be the reason that our grandparents even exist.
Humans are among the few species that continue to live after menopause, which might be because of the evolution-proven support that older women provide when it comes to raising children.
The new findings suggest that pressure from pathogens like gonorrhea developed human gene mutations that protected elderly people from cognitive decline and made sure they could live longer.
The discovery comes by comparing human and chimpanzee genomes. The comparison revealed that humans have their own unique version of the gene for CD33, a receptor in immune cells that plays an important role in binding to a type of sugar called sialic acid. Human cells are coated with it and it helps immune cells "recognize" other cells and not attack them.
"Somewhere along the evolutionary line, humans picked up an additional mutated form of CD33 that is missing the sugar-binding site," the authors said. "The mutated receptor no longer reacts to sialic acids on damaged cells and plaques, allowing the microglia to break them down. Indeed, higher levels of this CD33 variant were independently found to be protective against late-onset Alzheimer's."
It would seem that CD33 was selected by evolution for its survival advantages, later making sure that humans were able to have big families that represent several generations. All of this, albeit indirectly, thanks to gonorrhea.