Mutation theory

Genetic Basis of Evolution and Speciation
Theories of organic evolution 
Mutation theory
Synthetic theory
Evolution at molecular level
Evolution of proteins
Evolution of nucleotide sequences
Molecular evolution in test tube
Modes of speciation
Mutation theory
Hugo de Vries (1840-1935), a Dutch botanist proposed the Mutation Theory in his book 'The Mutation Theory' Vol. I, in which he described a large number of monstrosities and new types in many species including his own work on genus Oenothera. O. lamarckiana, the only species out of 100 he collected, was observed to throw off types. These new types appearing due to sudden heritable changes were called new species by him, and the event was termed 'mutation'. A new type, much larger in size than the normal was described as a new species, O. gigas. As mutations are known to be random, the evolution was also considered to be random. No importance was attached to natural selection by the geneticists supporting the mutation theory. They also thought that there are no adaptations, but only chance preadaptations. However, it was later discovered that most of the mutations described by de Vries were due to structural and numerical variations in chromosomes, resulting from abnormal meiosis in O. lamarckiana (Structural Changes in Chromosomes), and were not due to point mutations. This theory also overcomes some of the objections raised against Darwinism, since it recognizes the role of discontinuous variations or sudden changes, called 'sports' by Darwin and 'mutations' by de Vries. Cases of ove -specialization of Dinosaurs, for example, can be easily explained on this basis. Origin of hereditary variations can also be explained and they can be distinguished from other environmental variations.

It is now known that the mutation theory in its original form, as proposed by de Vries, where natural selection was discarded, does not hold good. The mutations, as we know them to-day, however, do play a very important role in evolution but are not the only force working for organic evolution. There are other forces also working for it. Keeping in mind the above facts, the modern Synthetic Theory was proposed.