The members of the population have heritable variations.
The populations produce more offspring than the resources of the environment can support.
The individuals that have favorable traits survive and reproduce to a greater extent than those that lack these traits.
Over time,the proportion of the favorable trait increases in the population, and the population becomes adapted to the environment.
This means that the more favorable of the species will adapt to their environment and live long enough to reproduce and pass along these traits. With the ever changing environment