In a population of peacocks, there is an overproduction and variation within the species as the size, and brightness of the male peacock's tail feathers are different but play a vital role in understanding sexual selection
In order for a male peacock to reproduce, it must attract peahens using its tail feathers. The environment and peahens favor the peacocks with the biggest and brightest tail feathers.
The male peacocks with the brightest and largest tail feathers are chosen and mate passing this gene onto their offspring.
The male peacocks without big and bright tail feathers die off and don’t reproduce.
Eventually, all male peacocks will have big and bright tails, causing the species of peacocks to change unless they all die before reproducing