Final answer:
Evolutionary biologists have determined the origins of HIV by studying the virus's genetic material and how it evolves, indicating it originated in monkeys and jumped to humans.
Step-by-step explanation:
Evolutionary biologists have been able to determine the origins of HIV by analyzing genetic and biochemical evidence. Since viruses do not leave behind fossil records, scientists extrapolate data from how contemporary viruses evolve.
Comparing the genetic information of HIV with that of similar viruses in different species led to the discovery that HIV likely originated in monkeys and was then transmitted to humans, a process known as zoonotic transfer. This likely occurred in West Africa during the early to mid-1900s.
In addition to historical genetic analyses, a notable finding by American geneticist Stephen J. O'Brien and colleagues identified a deletion mutation, CCR5-delta 32, which provides resistance to HIV infection in some individuals of Eurasian descent.
The presence of this mutation in the population supports the understanding that HIV has a natural origin and suggests evolutionary adaptation in human populations exposed to the virus.
This ongoing evolution is also evident in the way HIV quickly develops drug resistance. The virus can replicate a billion times in a day, leading to a population of viruses within a treated patient that is entirely resistant to the drugs within weeks.
This rapid adaptation and the presence of natural resistance in certain human populations underscore that evolution is not a historical event but an ongoing process.