Crossing over in meiosis. Random fertilization in two gametes ( male sperm, female egg ) and the random way chromosomes line up in meiosis. To a lesser extent, mutation.
Genetic drift in small population results in fixation of a gene or loss of gene affecting only that particular population . It has no direct effect on diversity of organisms .
The more genetic diversity in a population, the more differences there will be in the traits of different individuals in the population. The way natural selection works is that some traits will cause...