Natural Selection

Resistance to atherosclerosis- Atherosclerosis is a disease that is produced by modern diets and lifestyles. Atherosclerosis is a type of arteriosclerosis. This is the thickening and hardening of arteries as people age. It involves deposits of fatty substances, cholesterol, cellular waste products, calcium and other substances in the inner lining of an artery. The deposits build up and cause a plaque. Plaque blockages are especially harmful when they break up and move forming a blockage elsewhere which may lead to a heart attack or even a stroke.There is, however, a town in Italy whose residents are resistant to atherosclerosis. The resistance can be traced back all the way to the original host of the mutation. Natural selection has kept this resistance present even in the most recent generations.

Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. It is one of several mechanisms that give rise to the evolution of biological species (other mechanisms include genetic drift and gene flow.) However, natural selection has a special significance because it is believed to be the one responsible for organisms being adapted to their environment. The theory of natural selection was proposed by Charles Darwin and Alfred Russel Wallace in 1858, though vaguer and more obscure formulations had been arrived at by earlier workers.

Natural selection can be subdivided into two types: (i) ecological selection, which arises from the portion of an organism's environment not related to direct sexual competition (such as the availability of food, the presence of predators, and so forth); and (ii) sexual selection, which arises from the competition for mates between individuals of the same sex. The reason for this division is that the effects of sexual selection can produce results that seem counterintuitive from the point of view of ecological selection alone (a famous example being the tails of peacocks, which, though cumbersome, serve an important purpose in courtship displays.)

Natural selection is distinguished from artificial selection, which is the alteration of domesticated species resulting from human intervention as opposed the "natural environment". However, the mechanisms of natural and artificial selection are essentially identical, and in fact the observed effects of artificial selection were used by Darwin to illustrate how natural selection works.

The modern theory of natural selection is formulated in terms of genetic differences between individuals, resulting in differences in the frequency of alleles in a population over successive generations. The genetic variation on which natural selection acts are now understood to arise from random mutations.

The process of natural selection requires 3 ingredients, 1) variation, 2) a struggle for survival, and 3) survival of the fittest. 1) Variation. For the process of natural selection to occur there must be variation among individuals in a population and this variation must have a genetic basis. The variation may be in morphological, physiological or behavioral characteristics. As humans, we are most aware of the variation among members of our own species, exhibited by the girls in this picture, but there is variation among individuals of every species.

Although some of the variation is the result of environmental influences,