Natural Selection In the previous sections, you have already learned how changes to genes can take place in organisms. This gives rise to a wide variety species. The genes that these species have control their characteristics. In the long run, only those species that have qualities better adjusted to the natural environment can live longer. These organisms will usually have better ability to find or store food, or are more able to escape their predators. Thus, these organisms have more chance to mate and give birth to more and healthier off-spring. Over the years, the total number of this species will increase in number, while the less fit species will decrease in number. Eventually, the lesser fit species will become extinct, and only the fittest will survive. One of the clearest examples of natural selection at work in the modern world is afforded by gene-frequency changes in carefully studied populations of the peppered moth, a species of the genus Biston found in England. These moths, originally light grayish but with a small proportion of dark-colored individuals, are eaten by birds that locate them visually. When the British countryside near cities became blackened by smoke from industrial processes, the lighter moths, previously well disguised against light-colored tree trunks, were easily found by birds and thus became less fit. The dark moths became common because they were more difficult to discern against the darker background. A single gene, coding for the dark color rather than the light color, was spread by means of natural selection and raised to a high frequency in industrial regions.

	At first, white moth are selected for as their appearance can blend into the surrouding.
	Later, they are selected against as the blackened trees made them obvious to their predators.
	Relating Topics - Theory of Evolution - Artificial Selection