BIO254:NaturalSelection

Definition

Natural Selection is the process through which individuals with beneficial traits are more likely to survive and reproduce, and have better chances to pass on the traits to progeny, if the traits have heritable components. In the next generation, those traits tend to be more common. Through generations of accumulation, the traits will spread in the population, and can result in speciation and adaptation. On the other hand, individuals with injurious variations will have less chances to survive or reproduce, and their traits are less likely to be inherited and may be eliminated from the population.

The concept of “Natural Selection” was first introduced by Charles Darwin in his 1859 book “The Origin of Species by Means of Natural Selection”, by saying “…individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind. On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection. " Natural Selection provides one of the most important mechanisms on evolution.

Genetic Basis of Natural Selection

After genetics and population biology were incorporated into the studies of evolution, people get a better understanding of natural selection. The existence of genes was first suggested by Gregor Mendel, in the 1860s. In 1910s, T. H. Morgan introduced the chromosome theory of inheritance, R. A. Fisher showed how continuous variation could be the result of the action of many discrete loci. Morgan's student Theodosius Dobzhansky was the first to apply Morgan's chromosome theory and the mathematics of population genetics to natural populations of organism. Their works, as well as contributions from many other scientists shed light on the genetic basis of natural selection.

Traits of an organism are coded by their genes. But for each gene, there might be some variations, or so-called different alleles. The genetic variation arises from random mutation and recombination, and provides the sources for natural selection. Populations evolve by changes in the relative allele frequency brought about by random genetic drift, gene flow, and especially natural selection. Different alleles may give rise to different traits, or phenotypes. Individuals with the phenotypes favorable for surviving or reproduce have more chances to pass the alleles to the offspring, so that the allele frequency will increase in the population. The favorable genetic variants may have individually slight phenotypic effects and phenotypic changes are gradual. Given enough time, the gradual evolution could give rise to changes of great magnitude, such as reproductive isolation, and result in speciation or designation of higher taxonomic levels.

Natural Selection vs Artificial Selection

The Process of Natural Selection

Research History of Natural Selection

Pre-Darwinian Theories

Lamarckian idea of inheritance of acquired characteristics

Darwin

Neo-Darwinism

References

Darwin C. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life John Murray, London; modern reprint Charles Darwin, Julian Huxley (2003). Chapter 4 - Natural Selection.

Futuyma, D.J. in Evolutionary Biology, Sinauer Associates, 1986; p.12

Wikipedia, http://en.wikipedia.org/wiki/Natural_selection

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25 April 2024