Evolution
|
This article provides an overview of the Evolution of populations and the mechanisms that derive it.
What is Evolution?
The theory of evolution explains how populations of organisms have changed over time. Evolution does not refer to changes that occur in an individual within its lifetime but it refers to changes in the characteristics of populations over the generations. These changes, which include modifications in structure, physiology, ecology and behaviour, may be so small that it is difficult to detect them or such great that the population differs from its ancestral population noticeably. Eventually, two populations may diverge to such a degree that we refer to them as different species.
Evolution has two main perspectives: microevolution and macroevolution. The evolution of populations is best understood in terms of phenotype, genotype and allele frequencies.
Evolution - Deriving Mechanisms
Two major mechanisms drive evolution; the first is natural selection and the second is genetic drift. Other mechanisms evolving in the evolutionary process are:
Each population possesses a gene pool including all the alleles for all the genes present in it. Allele and/or genotype frequencies may be changed by the evolution deriving mechanisms.
Natural Selection
Charles Darwin, in his 1859 seminal book, “On the Origin of Species”, named the differential survival and reproductive success of individuals as natural selection. By natural selection, individuals of a population that enjoy more successful adaptations to the environment have more chances to survive and reproduce. Natural selection fights back seriously abnormal phenotypes as well as eliminates harmful mutations or reduces them. Over successive generations, the proportion of favourable alleles cause the population to increase. In contrast with other microevolutionary processes such as non-random mating, mutation, genetic drift and gene flow, natural selection leads adaptive evolutionary change. Natural selection explains why organisms are well adapted to the environments in which they live but also helps to account for the diversity of life. Natural selection enables populations to change, thereby adapting to different environments and different ways of life. It is the differential reproduction of individuals with different traits, or phenotypes (and therefore different genotypes) in response to the environment. Natural selection results in the preservation of individuals with favourable phenotypes and elimination of those with unfavourable phenotypes. Individuals that are able to survive and produce fertile offspring have a selective advantage. The mechanism of natural selection does not cause the development of “perfect” organisms; it wipes out those individuals whose phenotypes are not as well adapted to the environment as other, while allow better adapted individuals to survive and reproduce. Reduction of the frequency of alleles that result in the expression of less favourable traits, the probability that favourable alleles responsible for an adaptation will come together in the offspring is increased. Genetic variation that confers no detectable selective advantage is called neutral variation
Genetic Drift
Please note that others may also have edited the contents of this article.
|
