Blackwell Publishing

The rise of evolutionary biology - What was the impact of Mendel's theory of inheritance?


From population genetics, the modern synthesis spread into other areas of evolutionary biology.

• Speciation. The question of how one species splits into two - the event is called speciation - was an early example. Before the modern synthesis had penetrated the subject, speciation had often been explained by macromutations or the inheritance of acquired characters. The question of how species originate is closely related to the questions of population genetics, and Fisher, Haldane, and Wright had all discussed it. The classic work, however, was by Ernst Mayr: Systematics and the Origin of Species (1942).

• Systematics. A related development is often called 'the new systematic', after the title of a book edited by Julian Huxley (1940). It refers to the overthrow of one concept of species and its replacement by a species concept better suited to modern population genetics.

Species were defined as a set of more-or-less similar looking organisms, where similarity was measured relative to a standard (or 'type') form for the species. Population geneticists came to define the members of a species by the ability to interbreed rather than by their morphological similarity to a type form. The modern synthesis had spread to systematics.

• Paleontology. Many paleontologists in the 1930s still persisted in explaining evolution in fossils by some inherent (and unexplained) tendency of a species to evolve in a certain direction. This is an idea related to the pre-Mendelian concept of directed mutation. All the evidence from the fossil record is perfectly compatible with the population genetic mechanisms discussed by Fisher, Haldane, and Wright.

The image opposite is of J.B.S. Haldane (1892-1964) photographed in Oxford in 1914.

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