What does selection pressure refer to?

Selection pressure refers to the environmental factors that favor certain phenotypes, which means it influences which individuals in a population are more likely to survive and reproduce based on their traits. These factors can include elements like predation, competition for resources, disease, and environmental changes. When certain traits confer a survival advantage in a specific context, individuals with those traits are more likely to pass them on to the next generation. This leads to a change in allele frequencies within the population over time, a key aspect of the process of natural selection.

In contrast, random mating within a population does not inherently favor specific traits; it simply determines how genes are shuffled during reproduction. While genetic variation is crucial for evolution and selection to act upon, it does not itself constitute selection pressure. Lastly, the size and health of a population can influence its genetic stability and resilience but are not directly related to the concept of selection pressure, which specifically targets the influence of environmental factors on the survival and reproduction of individuals based on their phenotypic traits.