The Elements of Evolution (39) Saltation


Natural selection acts only by taking advantage of slight successive variations; she can never take a great and sudden leap, but must advance by short and sure, though slow steps. If it could be demonstrated not by numerous, successive, slight modifications, my theory would absolutely break down. ~ Charles Darwin

A sudden leap in specific evolution is termed saltation. Before Darwin, most evolutionary theorists were saltationists. Lamarck was generally a gradualist but thought that saltation was possible.

Darwin’s speculations on evolution were not immediately favored because of his insistence on gradualism alone.

Mr. Darwin’s position might have been even stronger than it is if he had not embarrassed himself with the aphorism, “Natura non facit saltum,” which turns up so often in his pages. Nature does make jumps now and then, and a recognition of the fact is of no small importance in disposing of many minor objections to the doctrine of transmutation [i.e., Darwin’s theory]. ~ English biologist Thomas Henry Huxley in 1864, in review of Darwin’s On the Origin of Species (1859)

William Bateson, who coined the term genetics, rhetorically riposted in 1894: “Species are discontinuous. May not the variation by which species are produced be discontinuous too?” Like Huxley and others, Bateson bemoaned the “gratuitous difficulties which have been introduced by this assumption” by Darwin of gradualism.

Others thought that Darwin’s emphasis on gradualism had not gone far enough. Scottish engineer Fleeming Jenkin wrote an article in 1867 that convinced Darwin that he had not been insistent enough about incrementalism. In response, Darwin added a section in the 1869 5th edition of Origin that slammed the door on saltation.

In the early 20th century, incipient geneticists rallied around the notion that saltation might be caused by large mutations. English geneticist Reginald Punnett supported a saltational theory in his 1915 book Mimicry in Butterflies.

German-born American geneticist Richard Goldschmidt is considered the first to integrate genetics, development, and evolution. In 1933, he proposed macroevolution via macromutation, an idea that was universally rejected and became ridiculed as the “hopeful monster” hypothesis.

The change from species to species is not a change involving more and more additional atomistic changes, but a complete change of the primary pattern or reaction system into a new one, which afterwards may again produce intraspecific variation by micromutation. ~ Richard Goldschmidt in The Material Basis for Evolution (1940)

Saltation staggered in the wake of the neo-Darwinist school that reconciled Mendelian genetics with natural selection. This became the reigning religion of evolutionary biologists and remains so to this day.

As an a priori bias, phyletic gradualism has precluded any fair assessment of evolutionary tempos and modes. The general preference that so many hold for gradualism is a metaphysical stance embedded in the modern history of Western culture: it is not a high-order empirical observation, induced from the objective study of Nature. ~ American evolutionary biologist Stephen Jay Gould in 1977

Saltation’s slump did not last, as continuing research found hopeful monsters.

The past 20 years have vindicated Goldschmidt to some degree. With the discovery of the importance of regulatory genes, we realize that he was ahead of his time in focusing on the importance of a few genes controlling big changes in organisms, not small-scales changes in the entire genome as neo-Darwinians thought. The hopeful monster problem is not so insurmountable after all. ~ American paleontologist Donald Prothero in 2007

Saltational evolution is targeted and relatively rapid change in specific characters and their coding genes. ~ American entomologist Daniel Rubinoff & South African evolutionary biologist Johannes Le Roux

Saltation works via genic edits, often epigenetic in origin, which modify development and produce a significant change.

Plant hybridization, and its resistance, sometimes suggests saltation. Hybrids via allopolyploidy are saltational. Mixed populations of related plants that naturally resist hybridization indicates saltation.