neo-Darwinism

   Charles Darwin knew nothing of the mechanism of heredity when he proposed his theory of evolution, even though this was some forty years after Mendel had initiated the study of genetics through his work on pea heredity. Neo-Darwinism is the assimilation of genetics into Darwinian evolutionary theory; the term is given to the paradigm which emerged from the synthesis of the key tenets of Darwin’s theory of evolution by natural selection and of Mendel’s discovery of the units of heredity, subsequently understood as genes. Neo-Darwinian theory was initially proposed by J.B.S.Haldane and R.A. Fisher, among others, and states that evolution of diversity proceeds by the progressive selection of organisms which are different by virtue of mutations which occur randomly in their genes.

   While key elements of basic neo-Darwinian theory remain within current views of evolution, subsequent evidence has suggested that many different processes and events have played and will continue to play an important part in the evolution of the diversity of organisms in the biosphere. Many more may yet remain to be discovered. Many processes contribute to the rate of evolution of diversity in addition to simple mutations, including: (1) the symbiotic theory of evolution which proposes that the consolidation over time of collaborations (symbioses) between different types of simpler cells (bacteria) gave rise (and may yet give rise) to more complex cells (the eukaryotic cells of plants and animals); (2) the knowledge that extracellular agents like viruses can transport genetic material (genes) between cells; (3) the relatively recent discovery that genes are divided into segments of coding and non-coding DNA which might lead to rather large changes in the structure of gene products from a single mutation at a segment boundary; and (4) that simple mutations in genes which play key orchestrating roles in embryogenic development can lead to rather large changes in the overall structure of the adult organism.

   While these various mechanisms for altering gene structure provide the engine for evolution, the process of diversification requires also the range of environmental conditions which exist in different geographical locations and at different times (for example, the ice ages). These are the environments which will favour or penalize organisms with particular characteristics and perhaps initiate divergent lineages of organisms which are more successful than average in those environments.

   See also: Dawkins, Richard

   Further reading

    Ho, M. (1984) Beyond Neo Darwinism, London: Academic Press.

   PETE SHETERLINE