Saltation (biology)

In biology, saltation (from Latin, saltus, "leap") is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism. The term is used for nongradual changes (especially single-step speciation) that are atypical of, or violate, gradualism—involved in modern evolutionary theory. An example would be the origin of the feather.

Prior to Charles Darwin most evolutionary scientists had been saltationists.Jean-Baptiste Lamarck was a gradualist but similar to other scientists of the period had written that saltational evolution was possible. Étienne Geoffroy Saint-Hilaire endorsed a theory of saltational evolution that "monstrosities could become the founding fathers (or mothers) of new species by instantaneous transition from one form to the next." Geoffroy wrote that environmental pressures could produce sudden transformations to establish new species instantaneously. In 1864 Albert von Kölliker revived Geoffroy's theory that evolution proceeds by large steps, under the name of heterogenesis.

With the publication of On the Origin of Species in 1859 Charles Darwin had denied saltational evolution by writing that evolutionary transformation always proceeds gradually and never in jumps. Darwin insisted on slow accumulation of small steps in evolution and wrote "natural selection acts solely by accumulating slight successive favourable variations, it can produce no great or sudden modification; it can act only by very short steps". Darwin continued in this belief throughout his life.

From 1860 to 1880 saltation had a minority interest but by 1890 had become a major interest to scientists. In their paper on evolutionary theories in the 20th century (Levit et al. 2008) wrote:

The advocates of saltationism deny the Darwinian idea of slowly and gradually growing divergence of character as the only source of evolutionary progress. They would not necessarily completely deny gradual variation, but claim that cardinally new ‘body plans’ come into being as a result of saltations (sudden, discontinuous and crucial changes, for example, the series of macromutations). The latter are responsible for the sudden appearance of new higher taxa including classes and orders, while small variation is supposed to be responsible for the fine adaptations below the species level.

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