Genetic drift along with natural selection, mutation, and migration is
one of the basic mechanisms of evolution.
In each generation, some individuals may, just by chance, leave behind a
few more descendents (and genes,
of course!) than other individuals. The genes of the next generation will
be the genes of the "lucky" individuals, not necessarily the healthier
or "better" individuals. That, in a nutshell,
is genetic drift. It happens to ALL populations there's
no avoiding the vagaries of chance.
Earlier we used this hypothetical cartoon. Genetic drift affects the genetic
makeup of the population but, unlike natural
selection, through an entirely random process. So although genetic drift
is a mechanism of evolution, it doesn't work to