Final answer:
Natural selection influences human variation, seen in the persistence of lactase production in some populations and the variation in human skin pigmentation. These traits evolved as adaptations to dietary availability and different levels of UV radiation exposure.
Step-by-step explanation:
Natural Selection and Human Variation
Natural selection is a mechanism of evolution where individuals with favorable inherited traits are more likely to survive and reproduce. Over time, these traits become more common in a population.
Two examples illustrating how natural selection has influenced human variation include the adaptation to post-agricultural diets and the changes in human skin pigmentation.
One well-known example is the persistence of lactase production into adulthood in certain human populations, such as those in Europe, where dairy farming became prevalent. This adaptation allows adults to digest lactose in milk, providing a nutritional advantage in environments where dairy products are available.
Consequently, the allele for lactase persistence increased in frequency within these populations due to the survival and reproductive advantage it conferred.
Another example is the variation in human skin pigmentation across different geographical regions. This variation is thought to be an evolutionary response to different levels of ultraviolet (UV) radiation exposure.
Darker skin pigmentation provides protection against UV-induced damage and helps prevent folate depletion in regions of high UV exposure, while lighter skin enhances UV-induced vitamin D production in regions with less sunlight.
These examples showcase the ongoing process of natural selection acting on human populations, leading to adaptations in response to environmental pressures.