What is a factor that causes selection for particular alleles?

Selection pressure is a key factor that influences which alleles are favored in a population. It refers to environmental factors that affect the survival and reproduction of individuals within that population. When certain traits confer advantages in terms of survival or reproductive success, individuals with those traits are more likely to pass on their alleles to the next generation. This leads to an increase in the frequency of those advantageous alleles in the population over time.

For example, in a scenario where a population faces a change in its environment, such as a new predator or a change in available food sources, individuals who possess traits that help them evade predators or utilize food more effectively will have a higher chance of survival. As a result, the alleles that code for those advantageous traits will be selected for, leading to their prevalence in future generations.

In contrast, factors like mutation rate primarily impact the introduction of new alleles rather than their selection. Population density can influence competition and social behaviors but does not directly cause selection for specific alleles. Carrying capacity relates to how many individuals an environment can support, but it is more about resource limitations than the selective advantages of specific traits. Thus, selection pressure plays a critical role in shaping the genetic makeup of populations through natural selection.