Molecular mechanisms driving Darwinian evolution

Abstract

According to the Neodarwinian theory, biological evolution depends (1) on the availability of genetic variants, (2) on natural selection exerted on all available forms of life and (3) on geographical and reproductive isolation. The now available methodology of molecular genetics enables us to explore the molecular nature of genetic variation. It has become clear that many different molecular mechanisms contribute to the overall production of alterations in DNA sequences. These mechanisms can be classified into three conceptually different natural strategies of genetic variation. These strategies differ in the quality of their contributions to biological evolution. Alterations in genomic DNA sequences can imply either (1) a small local sequence change or (2) the intragenomic rearrangement of DNA segments or (3) the acquisition of a DNA segment from another kind of organism by horizontal gene transfer. Combinations of these strategies can also be seen in single processes. In principle, genetic variation occurs more or less randomly rather than as a targeted response to an identified need. It is the natural selection together with the available forms of life that determine the directions that biological evolution takes. Interestingly, genetic variation nevertheless depends on products of so-called evolution genes. These products act as generators of genetic variations and/or as modulators of the frequency of genetic variation. The products of evolution genes exert their activities in close collaboration with various nongenetic factors such as structural flexibilities of biologically relevant molecules, chemical instability of nucleotides, random encounter, chemical and physical mutagens. In conclusion, natural reality cares actively for biological evolution, which should not any longer be seen as resulting from errors and accidents. Some philosophical, worldview implications will be discussed.