Natural selection is the greater chance of passing on of genes by the best adapted organisms.
Variation is natural or random changes in all living organisms.
Variation leads to survival of the fittest since the variations in certain organisms allow that organism to have an advantage over the others in its species in that area
The surviving organisms reproduce, since they don’t get eaten, so variation has caused the species to evolve.
Evolution is caused by natural selection which is caused by a change in the environment