We need a Selection criteria.
A simple selection method is each individual has the probability
From a population of individuals, we wish
to give the fitter individuals a better chance to survive to the
next generation. We do not want to use the simple criterion
"keep the best n individuals." It turns out nature does not
kill all the unfit genes. They usually become recessive for a
long period of time. But then they may mutate to something
useful. Therefore,
there is a tradeoff for better individuals and diversity.