A paradigm is a conceptual framework of ideas, methods and explanatory principles that allows scientists to tackle the questions in their field. One such paradigm is the Modern Evolutionary Synthesis.
The Modern Evolutionary Synthesis, formulated in the 1930s and 1940s, contributed to evolutionary thought by bridging the intellectual and cultural gaps between geneticists, naturalists, and paleontologists. Its tenets were several:
- All evolutionary phenomena can be explained in a way that is consistent with known genetic mechanisms and the observational evidence of naturalists.
- Evolution is gradual and is caused by small genetic changes, recombination and natural selection. Discontinuities among species are explained as originating gradually, through geographical separation and extinction rather than saltation. However, this does not mean that the rate of evolutionary change is constant. Several mass extinctions in the evolutionary history of life give us evidence that massive extinctions leave niches vacant, allowing other species to achieve rapid diversification and speciation.
- Selection is the main driver of change, even if variations in fitness are slight. The object of selection is the phenotype, the externally observable traits of an organism. This is produced by the interaction of the genotype, the heritable information in the form of DNA with its surrounding environment. As the genotype codes for the phenotype, and the genotype is passed through reproduction, the gene is the unit for selection. But as the phenotype are only the external traits, it is the genotype that create them which are selected for, specifically in the form of genes, packets of genetic information within the chromosome. The role of genetic drift is equivocal.
- The genetic diversity of natural populations is a key factor in evolution. But as evolution proceeds through natural selection, several genetic variations are selected against. Thus, natural selection destroys variation which it feeds upon. Also are barriers to gene flow, which are key infuences in genetic drift and speciation.
- The fossil record can be explained by extrapolating micro evolutionary observations to macro evolutionary events.
Traditionally, developmental biology, the study if the changes in structure of organisms throughout their life, was viewed as having played little role in the formulation of the modern evolutionary synthesis. However, in the late twentieth century, several biologists have considered and proposed that the statistical framework yielded by the Modern Synthesis was unable to account for several phenomena in biology such as niche construction, epigenetic inheritance and deep homology by which several metazoan phyla have in common. They proposed an "Extended Synthesis," in which several disparate areas of biology such as ecology and, in particular, embrology, would be united with the recent unification of Mendelian Genetics and Darwinian Natural selection which lead to the modern synthesis, or Neodarwinism. . The modern evolutionary synthesis has been continually developed, refined and challenged, and has led to the extension of the Darwinian paradigm of natural selection to include discoveries and concepts unknown to Darwin, such as DNA and genetics.
While the Traditional Evolutionary Synthesis is linked primarily to genetics, related work has been done in a number of fields including engineering, physics, biochemistry, proteiomics, game theory, statistics, ecology, economics, paleontology, embryology, chaos theory, systems theory, neuroscience and computing, that suggest that a future synthesis might be more inclusive.
- Huxley J.S. 1942. Evolution: the modern synthesis. Allen & Unwin, London. 2nd ed 1963; 3rd ed 1974.
- Mayr & Provine 1998
- Mayr E. 1982. The growth of biological thought: diversity, evolution & inheritance. Harvard, Cambs. p567 et seq.
- Pigliucci, Massimo 2007. Do we need an extended evolutionary synthesis? Evolution 61 12, 2743–2749.