Neo-Darwinism is the interpretation of Darwinian evolution through natural selection as it has variously been modified since it was first proposed. It was early on used to name Charles Darwin's ideas of natural selection separated from his hypothesis of pangenesis as a Lamarckian source of variation involving blending inheritance.[1]

In the early 20th century, the concept became associated with the modern synthesis of natural selection and Mendelian genetics that took place at that time.

In the late 20th century and into the 21st century, neo-Darwinism denoted any strong advocacy of Darwin's thinking, such as the gene-centered view of evolution.

As part of the disagreement about whether natural selection alone was sufficient to explain speciation, in 1880, Samuel Butler called Alfred Russel Wallace's view neo-Darwinism.[2][3]

The term was again used by George Romanes in 1895 to refer to the version of evolution advocated by Wallace and August Weismann with its heavy dependence on natural selection.[4]

Weismann and Wallace rejected the Lamarckian idea of inheritance of acquired characteristics that even Darwin took for granted.[5][6] The term was first used to explain that evolution occurs solely through natural selection, and not by the inheritance of acquired characteristics resulting from use or disuse.[7] The basis for the complete rejection of Lamarckism was Weismann's germ plasm theory. Weismann realised that the cells that produce the germ plasm, or gametes (such as sperm and egg in animals), separate from the somatic cells that go on to make other body tissues at an early stage in development. Since he could see no obvious means of communication between the two, he asserted that the inheritance of acquired characteristics was therefore impossible; a conclusion now known as the Weismann barrier.[8]

From the 1880s to the 1930s, the term continued to be applied to the panselectionist school of thought, which argued that natural selection was the main and perhaps sole cause of all evolution.[9] From then until around 1947, the term was used for the panselectionist followers of Ronald Fisher.

Following the development, from about 1918 to 1947, of the modern synthesis of evolutionary biology, the term neo-Darwinian was often used to refer to that contemporary evolutionary theory.[10][11]

Biologists however have not limited their application of the term neo-Darwinism to the historical modern synthesis. For example, Ernst Mayr wrote in 1984 that "the term neo-Darwinism for the synthetic theory [the modern synthesis of the early 20th century] is wrong, because the term neo-Darwinism was coined by Romanes in 1895 as a designation of Weismann's theory."[12][1][7][13] Publications such as Encyclopdia Britannica similarly use neo-Darwinism to refer to current evolutionary theory, not the version current during the early 20th century synthesis.[14] Richard Dawkins and Stephen Jay Gould have used the term in their writings and lectures to denote the forms of evolutionary biology that were contemporary when they were writing.[15][16]

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