Review how more offspring than an environment can support increases mortality, then how competition for limited resources promotes selection.
Outline how overpopulation of a species in a given environment may lead to evolution.
more are born than can survive;
there is variety/variability in the offspring;
competition for resources / struggle for survival / selection pressure;
only the most able/adapted survive / survival of the fittest;
the survivors reproduce and pass on genes;
genes of less able/adapted are eliminated / change in the gene pool;
natural selection occurs;