It's possible that the human immune system's battle with gonorrhea has the positive side effect of encouraging healthy brain cells later in life.
This little improvement in cognitive function in our later years may have helped ensure that grandmas were intelligent enough for evolution to preserve them.
Researchers at the University of California, San Diego are getting closer to some theories for why humans have survived past the eras where we can no longer reproduce, despite the fact that it is incredibly difficult – and maybe impossible – to do so.
Researchers working under the direction of molecular medicine professor Ajit Varki revealed in 2015 that humans differ from other primates in that we have a special form of immunological receptor that guards against Alzheimer's disease.
The scientists discovered in a report released this month that the emergence of this mutant immunological receptor in our species wasn't completely random, but rather was the product of strong selection pressure over a relatively short period of time.
The study revealed that this variety of immune receptors was not included into the genomes of some of our closest ancestors, Neanderthals and Denisovans. According to the researchers, something compelled us to create this unique immunological receptor early in our evolutionary history.
The most likely culprits are contagious infections unique to humans, including Neisseria gonorrhoeae, which try to blend in by dressing in the same sugar coating as human cells, deceiving immune cells on patrol into believing the bacteria are harmless.
The human immune system became highly adept at being duped into believing that gonorrhea was simply another human cell. However, the human immune system managed to strike back.
The researchers demonstrated that the newly developed immune receptor, as opposed to the earlier variant, could recognize the disguise and destroy the invasive germs.
Because gonorrhea may interfere with human reproduction, eliminating this illness is important for the survival of the species.
huCD33 is the name of the updated immunological receptor. It has long been the focus of research by evolutionary biologists because of the way this version has been altered into two barely distinct structures within our body.
The researchers hypothesize that once developed, this immunological receptor was likely co-opted by brain immune cells known as microglia for a distinct purpose: defense against aging.
Normally, the immune system of a person doesn't deliberately target itself, but when a cell begins to degrade, it must.
The huCD33 receptor has the extra benefit of being able to identify deteriorating brain tissue and so safeguard cognitive function in old age. It appears to have developed as a reaction to sly bacteria.
The huCD33 receptor is used by microglia to eliminate damaged brain cells and amyloid plaques linked to Alzheimer's disease. It is debatable if this may have paved the way for evolution to extend our lives by a few precious years in order to facilitate the upbringing of children.
Grandparents serve the human race by helping to care for children and transferring valuable cultural information. And the cause of that may be gonorrhea.
This paper was published in Molecular Biology and Evolution.
