Natural selection and evolutionary mechanisms

Natural selection is the very efficient and predictable means of evolution by which a species adapts to its environment, that results in evolutionary change as individuals with particular characteristics have a greater survival or reproductive rate than others in a population, and these genetic characteristics are then passed on to their offspring (Natural pp). In other words, natural selection is a consistent difference in survival and reproduction between different genotypes in what is referred to as reproductive success (Natural pp).

Although Charles Darwin's book, On the Origin of Species by Means of Natural Selection caused much ado when it was published in 1859, science now accepts that evolution is indeed a fact, and that natural selection effectively explains how adaptive evolution takes place (Natural pp).

There are two requirements that are essential in order for natural selection to occur (Evolution pp). One is that there must be heritable variation for some trait, such as beak size, color, thickness of skin, or fleetness (Evolution pp). And two, there must be differential survival and reproduction associated with the possession of that trait (Evolution pp). Adaptation by natural selection cannot occur unless both of these requirements are met (Evolution pp). For example, if some plants grow taller than others and are able to avoid being shaded by other, then they will produce more offspring, however, if they grow taller simply due to the type of soil their seeds land in, then no evolution will occur (Evolution pp). Moreover, if some individuals are faster than others because of the differences in their genes, but the predator is so much faster that it does not matter, then no evolution will occur, for example, if cheetahs ate snails (Evolution pp). Furthermore, natural selection can only choose among existing varieties in the population, therefore it might be useful for polar bears to have white noses, thus eliminating having to cover their noses with their paws when they stalk prey (Evolution pp).

Because there cannot be evolution without genetic variation, then there must be mutation and often recombination to generate the different genotypes or the different versions of the genes, called alleles, which may or may not make a difference in the ability of an organism to survive and reproduce (Natural pp). If there is simply no difference between the different genotypes or different genes in their impact on survival or reproduction, then what occurs are random changes of one vs. The other type in a population or a species until eventually one replaces the other (Natural pp). That is an evolutionary change that happens entirely by chance, by random fluctuations, and is called the process of genetic drift (Natural pp). Genetic drift is different from natural selection, which is a more consistent, predictable, dependable change in the proportion of one gene verse another or one genotype verses another, because there is some consistent superiority of one genotype verses another in a certain feature that affects its survival or some feature affecting its reproductive capabilities (Natural pp).