Neo-Darwinism is a term used to describe certain ideas about the mechanisms of evolution that were developed from Charles Darwin’s original theory of evolution by natural selection. The term was first used by George Romanes in 1895 to refer to the idea that evolution occurs solely through natural selection.
From the 1880s to the 1930s the term continued to be applied to the pan-selectionist school of thought, which argued that natural selection was the main and perhaps sole cause of all evolution.
Following the development, from about 1937 to 1950, of the modern evolutionary synthesis, now generally referred to as the synthetic view of evolution or the modern synthesis, the term neo-Darwinian has been used by some to refer to modern evolutionary theory. However, such usage has been described as incorrect. Despite this, publications such as the Encyclopaedia Britannica use this term to refer to current evolutionary theory. This term is also used in the scientific literature.
13.1 Evolution of Darwinism
13.1.1 Natural selection
The bio-geographical patterns Charles Darwin observed in places such as the Galapagos islands during the voyage of the Beagle caused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks on transmutation. Darwin’s observations led him to view transmutation as a process of divergence and branching. In 1838 he read the new 6th edition of “An Essay on the Principle of Population”, written in the late 1700s by Thomas Malthus. Malthus’ idea of population growth leading to a struggle for survival combined with Darwin’s theory of natural selection. Darwin did not publish his ideas on evolution for 20 years but he shared them with certain other naturalists and friends. During this period he used the time he could spare from his other scientific work to slowly refine his ideas and, aware of the intense controversy around transmutation, amass evidence to support them.
Unlike Darwin, Alfred Russel Wallace already suspected that transmutation of species occurred when he began his career as a naturalist. By 1855 his bio-geographical observations during his field work in South America and the Malay Archipelago made him confident enough in a branching pattern of evolution to publish a paper stating that every species originated in close proximity to an already existing closely allied species. Like Darwin, it was Wallace’s consideration of how the ideas of Malthus might apply to animal populations that led him to conclusions very similar to those reached by Darwin about the role of natural selection. In February 1858 Wallace, unaware of Darwin’s unpublished ideas, composed his thoughts into an essay and mailed them to Darwin, asking for his opinion. The result was the joint publication in July of an extract from Darwin’s 1844 essay along with Wallace’s letter. Darwin also began work in earnest on “The Origin of Species”, which he would publish in 1859.
13.1.2 1859–1930s: Darwin and his legacy
By the 1850s whether or not species evolved was a subject of intense debate. However, it was the publication of Charles Darwin’s “On the Origin of Species” that fundamentally transformed the discussion over biological origins. Darwin argued that his branching version of evolution explained a wealth of facts in biogeography, anatomy, embryology, and other fields of biology. He also provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection.
One of the first and most important naturalists to be convinced of the reality of evolution was the British anatomist Thomas Henry Huxley. Huxley recognized that Darwin’s theory provided a mechanism for evolution without supernatural involvement. By the early 1870s in English-speaking countries, thanks partly to these efforts, evolution had become the mainstream scientific explanation for the origin of species. Huxley made extensive use of new evidence for evolution from palaeontology. This included evidence that birds had evolved from reptiles, including the discovery of Archaeopteryx in Europe, and a number of fossils of primitive birds with teeth found in North America. However, acceptance of evolution among scientists in non-English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany, where both August Weismann and Ernst Haeckel championed this idea.
Darwin’s theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution. However, this theory could not explain several critical components of the evolutionary process. Specifically, Darwin was unable to explain the source of variation in traits within a species, and could not identify a mechanism that could pass traits faithfully from one generation to the next.