Why do male guppies have large colourful tail fin?

The large, colorful tail fins in male guppies have evolved as a result of sexual selection. Sexual selection is a process in which certain traits become more common in a population because they increase an individual's chances of finding a mate.

In the case of guppies, female guppies are known to prefer males with large, colorful tails. This preference is thought to have evolved because the large tail helps to increase the visibility and attractiveness of the male guppy. The more colorful the tail, the more likely it will attract the attention of a female guppy and lead to mating.

In summary, the evolution of large, colorful tail fins in male guppies is a classic example of sexual selection and demonstrates the importance of attractive visual traits in guppy mating preferences.