According to Douglas J. Futuyma, biological evolution can be defined as "change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions." (Evolutionary Biology, Sinauer Associates 1986) The question then arises how can one explain or even predict theses changes in the gene pool. In the mid 1800s Charles Darwin attempted to answer this question with his theory of Natural Selection
Natural selection can be thought of as constant interactions between living structures and their environment.
These interactions take the form of competitions among living organisms for available nutrients. The result is what is commonly referred to as "survival of the fittest", when those who are better able to obtain and make use of the nutrients survive at the expense of others. One being may better adapted to their environment that another because they have some variation in their DNA. This change can result form either a mutation in the nucleotide sequence of from sexual reproduction. Over time those with the variation will dominate the environment, and then the gene pool has been altered, evolution has taken place.
Natural selection is so important because it provides a link between chance and emergence. Only when the result of chance, like an advantageous mutation, is stabilized, an entry into the emergent layer is possible. This...