There are three ways the population of people with a specific trait may grow:
(i) Genetic drift: This is the random change in gene frequency that results from random fluctuations In this scenario, a particular characteristic with limited adaptive value and a survival advantage may become more common.
(ii)Natural selection is the process through which nature chooses features that are advantageous to the species in its environment. As a result, the prevalence of a certain trait chosen by nature rises.
(iii)Geographic isolation: Mountains, rivers, and the sea act as physical barriers that keep interbreeding communities apart. Because there is no gene flow between divided parts of the population as a result of this geographic isolation, the population with a particular character grows.