The mechanism of natural selection may have led to the evolution of the male quetzal's extraordinarily long tail feathers through sexual selection. Female quetzals may have preferred males with longer, more elaborate tail feathers, and thus mated with them more often. This would result in the offspring of these males inheriting the genes for longer tail feathers, which would gradually become more common in the population over time. As this process continued, the male quetzal's tail feathers may have become longer and more elaborate through successive generations.
Variation in a trait could be introduced into a population through mutation, which is a random change in an organism's DNA that can lead to a new trait. Alternatively, variation could be introduced through gene flow, which is the movement of genes from one population to another as a result of migration or other factors. For example, if a new population of organisms with a different form of a trait arrived in a previously homogenous population, this could introduce new variation into the population.
Evolution is the process by which populations of organisms change over time, as a result of changes in the inherited traits that define them. This can occur through natural selection, genetic drift, mutation, gene flow, and other mechanisms, and can lead to the development of new species and the extinction of others. Evolution is driven by the interactions between organisms and their environment, and the resulting changes in their traits and behaviors over time.