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Selection is an evolutionary “force” that leads to adaptation and change over time in a population of individuals. If selection were an engine, its fuel would be variation in heritable traits. If a particular variation (e.g., a longer tail) gives an individual a higher likelihood of producing offspring, that variation gives it a selective advantage. Over time, if selection continues to favor longer tails, the entire population will eventually exhibit the trait. Thus, the population will have evolved longer tails as an adaptation.

Here, we describe three primary types of selection—natural, sexual, and artificial—in an avian context. Click on the links above to explore the topic and learn about some amazing avian examples!