Darwin on Speciation
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Darwin on Speciation Laura van Holstein Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, Cambridge, UK
and Darwin’s later works is described here in full, and then it is placed in modern context to examine the cases for and against its accuracy and relevance to current evolutionary biology.
Darwin’s Explanation of Speciation Synonyms Darwin’s principle of divergence; Natural selection; Origin of Species
Definition Charles Darwin’s proposed mechanism(s) for the evolution of new species
Introduction It is evident from the title of Darwin’s seminal work that he sought to advance a theory of speciation – that is, to explain the causes and mechanisms of the origin of species. However, many historians of science hold that the question implicit in his title was never fully answered, primarily because he never concretely defined the concept of “species” in the first place and because he conjectured new species likely appeared in sympatry through the process of gradual divergence of characters. The theory of speciation as it is explained in The Origin
Darwin described speciation as the “mystery of mysteries” (1959, p. 1): how do new species appear? The essence of his answer is that “varieties” turn into new “species.” The specific meanings of these terms have been the subject of much modern debate (for a review see Mallet 2013) because they are used almost interchangeably, or so it seems. Darwin does define them as two nonequivalent but related units, and confusion arises because they are gradations of each other. Varieties are less discrete phenotypic clusters than species are. In other words, “. . .species are only strongly-marked or well-defined varieties” (1959, p. 55), but there is a degree of ambiguity regarding when a variety becomes distinct enough to be called a species: “. . .the amount of difference considered necessary to give two forms the rank of species is quite indefinite” (ibid., p. 59). The two keystones of Darwin’s explanation of speciation were the principles of natural selection and divergence. Natural selection is the differential survival of organisms resulting from differences in phenotype: characters better suited to the environment will tend to confer selective advantages to organisms that have them. These
© Springer Nature Switzerland AG 2020 T. K. Shackelford, V. A. Weekes-Shackelford (eds.), Encyclopedia of Evolutionary Psychological Science, https://doi.org/10.1007/978-3-319-16999-6_1387-1
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Darwin on Speciation
characters are therefore more likely to be passed on to the next generation, resulting in evolutionary change in populations over time. Darwin’s principle of divergence holds that sympatric organisms will suffer less from competition with each other if they diverge in character. The interaction of these two principles, and how this results in varieties evolving into distinct species over time, is described in chapter IV of The Origin: Only those variations which are in some way profitable will be preserved or naturally selected. And here the importance . .
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