Answer:
Sexual reproduction, where individuals of the same species exchange genetic material, allows for dissemination of nonlethal mutations in a gene pool.
Mutations with a positive impact on the survival of a population increase in frequency and the less successful version of the trait becomes less frequent.
A very successful mutation can be distributed through an open gene pool very quickly (by evolutionary standards), In some instances in a generation or two.
The Hardy Weinberg equation can be used to take a glimpse of this type of
change. The principle states that the frequency of an allele in a population will
remain the same. Note the statement allele, not trait.
Ex. W (the allele for white)
w (the allele for grey)
Moths that live in the forest before the industrial revolution need to hide on
white tree trunks so an WW or Ww moth is white and therefore safer than an
ww (grey) moth. All or most of the ww moths are eaten and do not get a chance to reproduce, so over time the w allele's frequency decreases. However, since it is recessive it will remain hidden in the population. The chance of two Ww individuals breeding to produce grey offspring will be decreased because there are so few of them.
Along comes the industrial revolution and many trees are covered with soot...now the WW and Ww moths show up on the sooty parts of the trees but the ww moths do not...now the w allele's frequency increases ww grey moths become prevalent in industrialized areas.
This is actually a true example of natural selection in action. I apologize for
not remembering the letter designation for the moth alleles...but the illustration is valid, none the less.