NCEA Level 3 Biology – Speciation (AS91605) Practice Exam

Directional natural selection is a process that promotes the survival and reproduction of individuals with a particular extreme phenotype within a population. This type of selection occurs when environmental conditions change, leading to an advantage for individuals that exhibit traits at one end of the phenotypic spectrum. For example, if a population of animals has a range of fur colors, and a change in the environment makes darker fur more advantageous (perhaps due to better camouflage), then individuals with darker fur will be more successful in surviving and reproducing. Over time, the frequency of the dark fur phenotype will increase in the population, pushing the overall distribution of phenotypes in that direction. This results in a shift away from the average or opposite extreme traits, focusing on the single extreme that provides a selective advantage. In this context, the option stating "One extreme phenotype" correctly identifies the focus of directional natural selection, illustrating how environmental pressures can lead to changes in the genetic makeup of a population over generations.