Recent (and not yet fully accepted) evidence suggests that chimpanzees and dolphins might suffer Alzheimer’s disease, or at least a condition that is similar enough to be comparable. Other than possibly those two species, humans are the only mammals to experience Alzheimer’s, the aggregation of amyloid-β and tau proteins into solid deposits that alter brain biochemistry for the worse. Why is this the case? What is it about our particular evolutionary path that resulted in this outcome? Might that teach us anything that could be used to suppress the development of the condition?
In this article, Alzheimer’s is painted as a consequence of antagonistic pleiotropy during the divergence of our species from other primates. Antagonistic pleiotropy is the name given to the theorized tendency for evolution to produce systems that are advantageous to young individuals but harmful to old individuals. Examples include systems that do not maintain themselves well, such as cells that lack enzymes to digest certain harmful forms of molecular waste, systems that have finite resources that run out, such as the adaptive immune system’s capacity to remember past pathogens, and systems that interact poorly with the damaged environment of old tissues, causing further damage – which is