Alternatives to Darwinian evolution

Where the fact of evolutionary change was accepted but the mechanism proposed by Charles Darwin, natural selection, was denied, explanations of evolution such as Lamarckism, catastrophism, orthogenesis, vitalism, structuralism and mutationism (called saltationism before 1900) were entertained.

Natural selection, with its emphasis on death and competition, did not appeal to some naturalists because they felt it immoral, leaving little room for teleology or the concept of progress (orthogenesis) in the development of life.

[1] The image of a ladder inherently suggests the possibility of climbing, but both the ancient Greeks and mediaeval scholastics such as Ramon Lull[1] maintained that each species remained fixed from the moment of its creation.

And if an animal had teeth adapted for cutting meat, the zoologist could be sure without even looking that its sense organs would be those of a predator and its intestines those of a carnivore.

[12] The Lamarckian social philosopher and evolutionist Herbert Spencer, ironically the author of the phrase "survival of the fittest" adopted by Darwin,[13] used an argument like Cuvier's to oppose natural selection.

[14] Where the fact of evolutionary change was accepted by biologists but natural selection was denied, including but not limited to the late 19th century eclipse of Darwinism, alternative scientific explanations such as Lamarckism, orthogenesis, structuralism, catastrophism, vitalism and theistic evolution[a] were entertained, not necessarily separately.

Natural selection, with its emphasis on death and competition, did not appeal to some naturalists because they felt it immoral, leaving little room for teleology or the concept of progress in the development of life.

[15][16] Some of these scientists and philosophers, like St. George Jackson Mivart and Charles Lyell, who came to accept evolution but disliked natural selection, raised religious objections.

[18] Some felt that natural selection would be too slow, given the estimates of the age of the earth and sun (10–100 million years) being made at the time by physicists such as Lord Kelvin, and some felt that natural selection could not work because at the time the models for inheritance involved blending of inherited characteristics, an objection raised by the engineer Fleeming Jenkin in a review of Origin written shortly after its publication.

[18][19] Another factor at the end of the 19th century was the rise of a new faction of biologists, typified by geneticists like Hugo de Vries and Thomas Hunt Morgan, who wanted to recast biology as an experimental laboratory science.

They distrusted the work of naturalists like Darwin and Alfred Russel Wallace, dependent on field observations of variation, adaptation, and biogeography, as being overly anecdotal.

Instead they focused on topics like physiology and genetics that could be investigated with controlled experiments in the laboratory, and discounted less accessible phenomena like natural selection and adaptation to the environment.

"[37] The American botanist Asa Gray used the name "theistic evolution"[b] for his point of view, presented in his 1876 book Essays and Reviews Pertaining to Darwinism.

[23][39] According to the historian Edward Larson, the theory failed as an explanation in the minds of late 19th century biologists as it broke the rules of methodological naturalism which they had grown to expect.

[40] Orthogenesis or Progressionism is the hypothesis that life has an innate tendency to change, developing in a unilinear fashion in a particular direction, or simply making some kind of definite progress.

[41][42] Support for orthogenesis fell during the modern synthesis in the 1940s when it became apparent that it could not explain the complex branching patterns of evolution revealed by statistical analysis of the fossil record.

[43][44][45] Moreover, the self-organizing processes involved in certain aspects of embryonic development often exhibit stereotypical morphological outcomes, suggesting that evolution will proceed in preferred directions once key molecular components are in place.

Lamarck also shared the belief, common at the time, that characteristics acquired during an organism's life could be inherited by the next generation, producing adaptation to the environment.

[48] Packard argued that the loss of vision in the blind cave insects he studied was best explained through a Lamarckian process of atrophy through disuse combined with inheritance of acquired characteristics.

[53] Catastrophism is the hypothesis, argued by the French anatomist and paleontologist Georges Cuvier in his 1812 Recherches sur les ossements fossiles de quadrupèdes, that the various extinctions and the patterns of faunal succession seen in the fossil record were caused by large-scale natural catastrophes such as volcanic eruptions and, for the most recent extinctions in Eurasia, the inundation of low-lying areas by the sea.

[55][56] Cuvier believed that the stratigraphic record indicated that there had been several such catastrophes, recurring natural events, separated by long periods of stability during the history of life on earth.

[57] Catastrophism has found a place in modern biology with the Cretaceous–Paleogene extinction event at the end of the Cretaceous period, as proposed in a paper by Walter and Luis Alvarez in 1980.

[63][64] Stuart Kauffman favoured self-organisation, the idea that complex structure emerges holistically and spontaneously from the dynamic interaction of all parts of an organism.

[63] Gerd Müller and Stuart Newman argued that the appearance in the fossil record of most of the current phyla in the Cambrian explosion was "pre-Mendelian" evolution caused by plastic responses of morphogenetic systems that were partly organized by physical mechanisms.

[69] Darwinian biologists have criticised structuralism, emphasising that there is plentiful evidence from deep homology that genes have been involved in shaping organisms throughout evolutionary history.

The primroses seemed to be constantly producing new varieties with striking variations in form and color, some of which appeared to be new species because plants of the new generation could only be crossed with one another, not with their parents.

[74] However, Hermann Joseph Muller showed in 1918 that the new varieties de Vries had observed were the result of polyploid hybrids rather than rapid genetic mutation.

[79] Carl Woese and colleagues suggested that the absence of RNA signature continuum between domains of bacteria, archaea, and eukarya shows that these major lineages materialized via large saltations in cellular organization.

The neutral theory allows for the possibility that most mutations are deleterious, but holds that because these are rapidly purged by natural selection, they do not make significant contributions to variation within and between species at the molecular level.

[89] By the start of the 20th century, during the eclipse of Darwinism, biologists were doubtful of natural selection, but equally were quick to discount theories such as orthogenesis, vitalism and Lamarckism which offered no mechanism for evolution.