Evolution

Darwin defined evolution in the Origin of Species as “descent with modification” (1). Although there have been various interpretations, modifications, and additions, the concepts of this definition continue to be repeated as biology develops. It seems likely that Darwin's definition will never fade away. Therefore, it is reasonable to state that evolution is the process in which the structures and functions of organisms are inherited from generation to generation, along with changes at both the morphological and molecular levels.

 In his theory, Darwin treated species as populations, and he recognized several features of populations that explain the process of evolution (1). In particular, he noticed that among individuals having variation in characteristics, those having advantageous characteristics, or “fitness,” can survive by producing more offspring of their own. This is the process of natural selection. Darwin already had advanced the concept that organisms have intrinsically inherited material labeled “genetic elements” (and later found to be DNA) and the idea that the variation found among individuals in a species was random, but these were not widely accepted. De Vries proposed the mutation theory, which states that mutations appear suddenly in a population and that species will experience periods of rapid mutation (2). His mutation theory and Mendel's law on inheritance, as well as Darwin's natural selection,were synthesized to create th e synthetic or neo-Darwin theory of evolution (3). The synthetic theory of evolution views evolution in the following way. First, mutation occurs to the genetic material, namely, DNA, in a random fashion. It is a source of genetic variation. and it is heritable to the next generation by Mendelian law. Natural selection then takes place so that individuals having advantageous characteristics can survive in a population, and the offspring have the same type of mutation, which becomes spread in a population. In this way, the genetic composition changes with the time.

The study of molecular evolution is essentially based on the synthetic theory of evolution. However, the development of molecular biology has introduced more detailed and new information on molecular mechanisms for producing genetic variation, which have accelerated the advancement of evolutionary studies. The genome projects currently in progress will give insights to the evolutionary changes of genomes, structures, and functions.

References

1. C. Darwin (1859) On the Origin of Species, Murray, London. 

2. H. De Vries (1901–1903) Die Mutationstheorie, Von Veit, Leipzig (1909–1910) "English translation", The Mutation Theory, trans. J. B. Farmer and A. D. Darbishire, Open Court, Chicago. 

3. E. Mayer and W. B. Provine (1980) The Evolutionary Synthesis, Harvard Univ. Press, Harbridge, MA.