Final answer:
An example of a human trait affected by genetic drift is the high incidence of certain diseases among the Afrikaner population due to the founder effect. This genetic drift resulted from a higher proportion of the founding colonists carrying specific mutations, which became common in this population compared to others.
Step-by-step explanation:
An example of a human trait that varies across populations due to genetic drift is the difference in disease incidence among the Afrikaner population of Dutch settlers in South Africa. The Afrikaners exhibit unusually high incidences of Huntington's disease (HD) and Fanconi anemia (FA), a result of the founder effect, a form of genetic drift. It occurred because a small group of Dutch colonists, who had a higher-than-normal proportion of certain mutations, founded the population. Over time, these mutations became much more common in the Afrikaner population than in the world at large due to the random chance of which individuals survived and reproduced and which did not, as opposed to natural selection.
Genetic drift is significant in small populations and can lead to significant changes in allele frequencies within a population. Catastrophic events, such as natural disasters, can cause a bottleneck effect, randomly reducing genetic variability and altering the population's genetic makeup. Similarly, when a group of individuals migrates to a new location and establishes a new population, the founder effect comes into play, potentially causing genetic traits that were rare in the original larger population to become relatively common in the new one.