How do diseases like AIDS and HIV form? Why after thousands of years did it only show up in the 20th century?

Question

How do diseases like AIDS and HIV form? Why after thousands of years did it only show up in the 20th century?

In: Biology

Answer 1

Diseases are the result of pathogens evolving to infect their host in such a way that they’re most likely to spread and propagate themselves while not being destroyed by the host’s immune system. This is an evolutionary arms war that is as old as time itself.

HIV and AIDS is an example of a disease that does those well. It shuts down the host’s immune response while keeping the host alive for decades so it can be spread to other hosts.

It only crossed over to humans from primates in recent history. In the primate population it would have persisted forever until primates evolved a resistance to it or it otherwise mutated into a different form that altered its characteristics unfavorably. This is the natural progression of almost all diseases.