What example of natural selection in humans is often cited?

The option highlighting the development of lactose tolerance in adult populations serves as a prominent example of natural selection in humans. This adaptation illustrates the relationship between genetic variation, environmental factors, and dietary practices.

Historically, most adult mammals, including ancestral humans, typically lose the ability to digest lactose, the sugar found in milk, after weaning. However, with the advent of pastoralism and dairy farming in certain cultures, some human populations started to consume milk into adulthood. Those individuals who possessed a genetic mutation allowing lactose digestion had a nutritional advantage in environments where dairy was a significant calorie source. Over time, natural selection favored these individuals, resulting in higher frequencies of lactase persistence (the ability to digest lactose) in populations that traditionally consumed dairy products.

This demonstrates a clear case of natural selection, as genetic adaptation occurred in response to dietary changes and environmental conditions, directly influencing survival and reproductive success in those populations.

The other options pertain to important adaptations or phenomena but do not exemplify the same clear causal relationship between genetic change and specific environmental factors as lactose tolerance does.