Final answer:
Lactose intolerance, sickle cell anemia, and HIV resistance exemplify ongoing evolution in humans by demonstrating adaptations and natural selection at work, with traits that confer survival advantages persisting and spreading in populations.
Step-by-step explanation:
Lactose Intolerance, Sickle Cell Anemia, and HIV Resistance
Lactose intolerance, sickle cell anemia, and HIV resistance are all examples of how evolution is currently occurring in humans. For instance, lactose intolerance is an adaptation to a past diet where adults rarely consumed milk; those with lactase persistence (the ability to digest lactose as an adult) represent a relatively recent adaptation in human history. Sickle cell anemia offers a more complex example. Despite the health problems it causes, the sickle cell trait provides a survival advantage against malaria, which is prevalent in certain regions like Africa. As such, the trait persists in populations where malaria is a threat, which demonstrates evolution through natural selection.
HIV resistance further illustrates ongoing human evolution. HIV reproduces very quickly, with a single virus capable of replicating itself a billion times in a 24-hour period. In a treatment scenario where the HIV population within a patient consists entirely of drug-resistant viruses after just a few weeks, it shows how those viruses with resistant genes survived the drug treatment and reproduced, whereas non-resistant viruses died off. This rapid change in the HIV population is the result of natural selection actively favoring the survival of resistant strains. Similarly, the rise of antibiotic-resistant bacteria in medical settings like hospital intensive care units, where drugs like Vancomycin are commonly used, shows how traits that confer drug resistance can rapidly become dominant in a population. Hence, these examples collectively provide evidence that evolution is an ongoing process in humans.