Final answer:
The claim that HIV was introduced into humans only once is false; HIV likely crossed over to humans from primates several times. It is a sexually transmitted disease that cannot be spread through casual contact and was first identified in 1981.
Step-by-step explanation:
The statement that HIV was likely introduced into humans only once is false. In reality, HIV likely crossed over to humans from primates on multiple separate occasions. This crossover event likely occurred in West Africa and probably happened during the early to mid-1900s. Since its identification in 1981, HIV has had profound impacts on global health, particularly in sub-Saharan Africa where the prevalence of HIV and subsequent AIDS cases is highest. It's also important to correct myths about HIV transmission; it cannot be spread through nonsexual contacts such as kissing, sharing glasses, or casual contact, and there is no evidence that it was created deliberately or accidentally by scientists.