Evolutionary biology and genetics have their roots some 150 years ago, but they were developed largely independently until about 1940 when it came to the modern evolutionary synthesis. Still at that time, the postulated gene was an abstract concept without known material basis. This should change, when microbial genetics was introduced in the 1940's. Very rapidly, it was discovered that DNA rather than any other biological molecules is the carrier of genetic information. It was a good coincidence that a few years later the structure of DNA could be identified as long filaments of double-helical molecules. It then became clear that genetic information could be stored in the linear sequences of nucleotides of DNA. While phenotypic variations, defined as mutations in classical genetics, could be shown to be caused by DNA sequence alterations, it became also clear that, and why, by far not all DNA sequence alterations cause a phenotypic change.
According to the neo-Darwinian theory of evolution, phenotypic variants are, together with their parental forms, the substrates for steadily exerted natural selection. The availability of genetic variants drives evolution, while natural selection, together with the available forms of life, directs evolution, and geographic and reproductive isolations modulate the process of evolution.
Efficient approaches are now available to study the molecular mechanisms that generate genetic variations. In microbial genetics, individual cases of spontaneous mutagenesis can be analysed experimentally. It has thereby become obvious that a number of different specific mechanisms are at work independently. In knowledge of these identified molecular mechanisms, one can compare DNA sequences from organisms that are more or less closely related. This allows one to conclude on their evolutionary history. This approach can be applied for functional domains, single genes, groups of genes and entire genomes of any kinds of living organisms.
The identified molecular mechanisms of genetic variation can be classified into three qualitatively distinct natural strategies, namely: (1) local sequence changes affecting one or a few adjacent nucleotides, (2) recombinational rearrangements of DNA segments within the genome, and (3) acquisition of a foreign DNA segment by horizontal gene transfer. Selected examples of these spontaneously occurring alterations in nucleotide sequences and in the genome structure will be discussed as well as their possible functional consequences.
The theory of molecular evolution that we also call "Molecular Darwinism" is based on the acquired knowledge on genetic variation. In genetic variation, products of evolution genes are involved as variation generators and/or as modulators of the rates of genetic variation. These evolution gene products act together with several non-genetic elements that can be assigned to intrinsic properties of matter, to environmental mutagens and to random encounter. We conclude that natural reality takes actively care of biological evolution. The evolution genes must have been fine-tuned for their functions by second-order selection, so that spontaneous genetic variation with different evolutionary qualities occurs at quite low rates. This ensures a relatively high genetic stability to individuals, as well as an evolutionary progress at the level of populations.
The presence of evolution genes points to a duality of the genome: while many genes act to the benefit of the individuals for the fulfillment of their lives, the evolution genes act to the benefit of an evolutionary development, for a slow, but steady expansion of life and biodiversity.
References for more detailed information:
W. Arber, Elements for a theory of molecular evolution, Gene, 317, 3-11 (2003).
W. Arber, Genetic variation and molecular evolution, In: R.A. Meyers (ed.), Genomics and Genetics, Wiley-VCH, Weinheim, Vol. 1, 385-406 (2007).
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