Neo-Darwinism is generally used to describe any integration of Darwin's theory of evolution by natural selection with Gregor Mendel's theory of genetics. It mostly refers to evolutionary theory from either 1895 (for the combinations of Darwin's and Weismann's theories of evolution) or 1942 (the "modern synthesis"), though it can mean any new Darwinian- and Mendelian-based theory such as the current evolutionary theory. The term Neo-Darwinism marks the combination of natural selection and genetics as it has been variously modified since it was first proposed.
Darwin's theory of evolution by natural selection, as published in 1859, provided a selection mechanism for evolution, but not a trait transfer mechanism. Lamarckism was still a very popular candidate for this. August Weismann and Wallace rejected the Lamarckian idea of inheritance of acquired characteristics that even Darwin took for granted. 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 eggs 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.
It is, however, usually George Romanes who is credited with the first use of the word in a scientific context. Romanes used the term to describe the combination of natural selection and Weismann's germ plasm theory that evolution occurs solely through natural selection, and not by the inheritance of acquired characteristics resulting from use or disuse, thus using the word to mean "Darwinism without Lamarckism."
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."
Publications such as Encyclopædia Britannica similarly use neo-Darwinism to refer to current evolutionary theory, not the version current during the early 20th century synthesis. 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.
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- Gould 2002, p. 216
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- Kutschera, Ulrich; Niklas, Karl J. (June 2004). "The modern theory of biological evolution: an expanded synthesis". Naturwissenschaften. 91 (6): 255–276. Bibcode:2004NW.....91..255K. doi:10.1007/s00114-004-0515-y. PMID 15241603.
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- "neo-Darwinism". Encyclopædia Britannica. Chicago, IL: Encyclopædia Britannica, Inc. 2015. Retrieved 2015-11-19.
- on YouTube. The video of the lecture was originally posted on May 5, 2010, at old.richarddawkins.net: "Lecture on Neo-Darwinism". Archived from the original on December 1, 2014. Retrieved 2013-07-07.CS1 maint: BOT: original-url status unknown (link).
- Gould 2011, pp. 53–73
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- Gould, Stephen Jay (2002). The Structure of Evolutionary Theory. Cambridge, Massachusetts: Belknap Press of Harvard University Press. ISBN 978-0-674-00613-3. LCCN 2001043556. OCLC 47869352.
- Gould, Stephen Jay (2011). "Challenges to Neo-Darwinism and Their Meaning for a Revised View of Human Consciousness". In McMurrin, Sterling M. (ed.). The Tanner Lectures on Human Values. 6. Salt Lake City, UT; Cambridge, UK: University of Utah Press; Cambridge University Press. ISBN 978-0-521-17647-7. OCLC 846869183. "Lecture delivered at Clare Hall, Cambridge University April 30 and May 1, 1984"