On the Origins of New Forms of Life

6.4: Saltation versus Gradualism



(Continued from the previous page)

During the eighty years following the publication of the Origin, many naturalists had saltationist views. Mayr comments that

Among those who accepted evolution after 1859 were not a few who were far more impressed by the occurrence of sudden mutations than was Darwin. Botanists and horticulturalists, in particular, cited numerous cases … where a strongly deviant type suddenly originated. … By the end of the 1880s this apparently had become the prevailing opinion."1

Prior to Darwin virtually all evolutionists had been saltationists.2 Étienne Geoffroy Saint-Hilaire (1772-1844), for example, thought birds must have arisen from dinosaurs by saltation.3 If anything, Cuvier was a more extreme saltationist than Geoffroy. Geoffroy said that new organs always arise by modification of ones preexisting in ancestral forms. "Cuvier, on the other hand," says Russell, "was always ready to admit Nature's power to form entirely new organs in response to new functional requirements."4 Karl Ernst von Baer (1792-1876), the founder of embryology, was a saltationist.5 In a series of essays6 he criticized Darwin's theory and instead explained evolution in terms of saltations guided by a vaguely defined "tendency to perfection." Richard Owen (1804-1892), the English comparative anatomist and paleontologist, "conceived change to have taken place by abrupt variation, independent of environment and habit."7 In his Anatomy of Vertebrates (1866-1868), he says this change takes place through "departures from parental type, probably sudden and seemingly monstrous, but adapting the progeny inheriting such modifications to higher purposes."8 William Bateson (1861-1926), coiner of the word genetics, wrote, "Species are discontinuous: May not the variation by which species are produced be discontinuous too?"9

Some had more balanced views. For example, Albert von Kölliker (1817-1905), the Swiss zoologist and histologist, entertained notions of evolution through saltation, but thought evolutionary change could also occur gradually. In his critique of Darwin's theory (Über die Darwin'sche Schöpfungstheorie, 1864), he maintained that "no transitional forms between existing species are known"10 and proposed his own theory of "heterogeneous generation." "The fundamental idea of this hypothesis," he said, "is that under the influence of a general law of evolution creatures produce from their germs others which differ from them." 11 But Kölliker did not stress saltation. In fact, he wrote that a

difference between the Darwinian hypothesis and mine is that I postulate many saltatory changes, but I will not and indeed cannot lay the chief stress upon this point, for I have not intended to maintain that the general law of evolution which I hold to be the cause of the creation of organisms, and which alone manifests itself in the activity of generation, cannot also so act that from one form others quite gradually arise."12,13

Darwin's friend Thomas Henry Huxley, too, felt that evolution could be either gradual or saltatory. In his review of the Origin, he wrote that

Mr. Darwin's position might, we think, 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. We believe, as we have said above, that 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].14

Bateson (1894: 15) also bemoaned the "gratuitous difficulties which have been introduced by this assumption." Indeed, Darwin here adopted the exact expression ("natura non facit saltum") the Scholastics had employed during the medieval era to express the idea that the "natural order" exhibited a continuous range of variation, their so-called "Law of Continuity."15

Others, however, thought Darwin's emphasis on minor change had not gone far enough in eschewing saltation. In 1867, a Scottish engineer, Fleeming Jenkin, attacked Darwin's theory in the June issue of the North British Review. Though Darwin had given saltational changes (which he called "single variations") short shrift in the first four editions of Origin, Jenkin's article convinced him that he had not been stringent enough. In a letter to Alfred Wallace, Darwin wrote,

F. Jenkin argued in the 'North British Review' against single variations ever being perpetuated, and has convinced me … I always thought individual differences more important; but I was blind and thought that single variations might be preserved much oftener than I now see is possible or probable.16

In the fifth edition of the Origin (1869) Darwin added a section further emphasizing his belief that selection of small individual differences was the paramount evolutionary force. After discussing a hypothetical case involving selection between slim and stocky wolves, he wrote the following:

It should be observed that, in the above illustration, I speak of the slimmest individual wolves, and not of any single strongly-marked variation having been preserved. In former editions of this work I sometimes spoke as if this latter alternative had frequently occurred. I saw the great importance of individual differences, and this led me fully to discuss the results of unconscious selection by man, which depends on the preservation of the better adapted or more valuable individuals, and on the destruction of the worst. I saw, also, that the preservation in a state of nature of any occasional deviation of structure, such as a monstrosity, would be a rare event; and that, if preserved, it would generally be lost by subsequent intercrossing with ordinary individuals. Nevertheless, until reading an able and valuable article in the 'North British Review' (1867), I did not appreciate how rarely single variations, whether slight or strongly-marked, could be perpetuated.17



(Works Cited)

1. Mayr (1982: 544).

2. Osborn (1894).

3. Russell (1982: 68), citing Geoffroy Saint-Hilaire (1833: 80).

4. Russell (1982: 305).

5. Russell (1982: 242).

6. In von Baer (1864–1876, vol. II). See: Über den Zweck in den Vorgängen der Natur, Über Zielstrebigkeit in den organischen Körpern inbesondere, and Über Darwins Lehre.

7. Russell (1982: 244).

8. Owen (1866–1868: vol. III, 797).

9. Bateson (1894: 18). Bateson and de Vries were bellwethers of genetic thought during the early years of the twentieth century. Bateson coined many of the terms used in the field of genetics today, such as allele, homozygote, and heterozygote (Cremer 1985: 191).

10. Translated by Huxley in his essay Criticisms on "The Origin of Species" (1864); reprinted in Huxley (1893–1894: vol. II, 88).

11. Translated in Russell (1982: 243).

12. Translated in Russell (1982: 243).

13. Saltationists often referred to vaguely defined laws governing evolution and they were frequently associated with the orthothogenetic, or vitalistic movement. Proponents of orthogenetic evolution claim that evolution is purposeful and directed. Vitalism is a doctrine claiming that the processes of life are not explicable by the laws of physics and chemistry alone. These thinkers made the error of attempting to explain a real, observed phenomenon (saltation) in terms of unobserved, undocumented phenomena (e.g., "vital impulse").

14. Huxley (1860).

15. Lovejoy (1936).

16. Darwin (1887: 107).

17. Darwin (1869: 103–104).

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