Natural selection is the differential survival and
reproduction of individuals due to differences in phenotype. It provides a
viable explanation for adaptation and speciation as it explains the change in
heritable traits characteristic of a population over time. Changes that allow an organism to better adapt
to its environment will help it survive and have more offspring. Natural
selection can change a species in small ways, causing a population to change
color or size over the course of several generations. Given enough time and
enough accumulated changes, natural selection can create entirely new species. It
can turn dinosaurs into birds, amphibious mammals into whales and the ancestors
of apes into humans.
"Overfishing and pollution have been blamed for the clam shortage, and scientists believe the harvest must be limited before the stock becomes exhausted."
