Orthogenesis

The possibility of progress is embedded in the mediaeval great chain of being, with a linear sequence of forms from lowest to highest. The concept, indeed, had its roots in Aristotle's biology, from insects that produced only a grub, to fish that laid eggs, and on up to animals with blood and live birth. The mediaeval chain, as in Ramon Lull's Ladder of Ascent and Descent of the Mind, 1305, added steps or levels above humans, with orders of angels reaching up to God at the top.[17]

The orthogenesis hypothesis had a significant following in the 19th century when evolutionary mechanisms such as Lamarckism were being proposed. The French zoologist Jean-Baptiste Lamarck (1744–1829) himself accepted the idea, and it had a central role in his theory of inheritance of acquired characteristics, the hypothesized mechanism of which resembled the "mysterious inner force" of orthogenesis.[1] Orthogenesis was particularly accepted by paleontologists who saw in their fossils a directional change, and in invertebrate paleontology thought there was a gradual and constant directional change. Those who accepted orthogenesis in this way, however, did not necessarily accept that the mechanism that drove orthogenesis was teleological (had a definite goal). Charles Darwin himself rarely used the term "evolution" now so commonly used to describe his theory, because the term was strongly associated with orthogenesis, as had been common usage since at least 1647.[18]

Reviewing Darwin's Origin of Species, Karl Ernst von Baer argued for a directed force guiding evolution.[19]

Ruse observed that "Progress (sic, his capitalisation) became essentially a nineteenth-century belief. It gave meaning to life—it offered inspiration—after the collapse [with Malthus's pessimism and the shock of the French revolution] of the foundations of the past."[20] The Russian biologist Karl Ernst von Baer (1792–1876) argued for an orthogenetic force in nature, reasoning in a review of Darwin's 1859 On the Origin of Species that "Forces which are not directed—so-called blind forces—can never produce order."[19][21][22] In 1864, the Swiss anatomist Albert von Kölliker (1817–1905) presented his orthogenetic theory, heterogenesis, arguing for wholly separate lines of descent with no common ancestor.[23] In 1884, the Swiss botanist Carl Nägeli (1817–1891) proposed a version of orthogenesis involving an "inner perfecting principle". Gregor Mendel died that same year; Nägeli, who proposed that an "idioplasm" transmitted inherited characteristics, dissuaded Mendel from continuing to work on plant genetics.[24] According to Nägeli many evolutionary developments were nonadaptive and variation was internally programmed. [2] Charles Darwin saw this as a serious challenge, replying that "There must be some efficient cause for each slight individual difference", but was unable to provide a specific answer without knowledge of genetics. Further, Darwin was himself somewhat progressionist, believing for example that "Man" was "higher" than the barnacles he studied.[25][26] Darwin indeed wrote in his 1859 Origin of Species:[27]

The inhabitants of each successive period in the world's history have beaten their predecessors in the race for life, and are, insofar, higher in the scale of nature; and this may account for that vague yet ill-defined sentiment, felt by many palaeontologists, that organisation on the whole has progressed. [Chapter 10][27]

As all the living forms of life are the lineal descendants of those which lived long before the Silurian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world. Hence we may look with some confidence to a secure future of equally inappreciable length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection. [Chapter 14][27]

Henry Fairfield Osborn's 1934 version of orthogenesis, aristogenesis, argued that aristogenes, not mutation or natural selection, created all novelty.[28] Osborn supposed that the horns of Titanotheres evolved into a baroque form, way beyond the adaptive optimum.[29]

In 1898, after studying butterfly coloration, Theodor Eimer (1843–1898) introduced the term orthogenesis with a widely read book, On Orthogenesis: And the Impotence of Natural Selection in Species Formation. Eimer claimed there were trends in evolution with no adaptive significance that would be difficult to explain by natural selection.[30] To supporters of orthogenesis, in some cases species could be led by such trends to extinction.[31] Eimer linked orthogenesis to neo-Lamarckism in his 1890 book Organic Evolution as the Result of the Inheritance of Acquired Characteristics According to the Laws of Organic Growth. He used examples such as the evolution of the horse to argue that evolution had proceeded in a regular single direction that was difficult to explain by random variation. Gould described Eimer as a materialist who rejected any vitalist or teleological approach to orthogenesis, arguing that Eimer's criticism of natural selection was common amongst many evolutionists of his generation; they were searching for alternative mechanisms, as they had come to believe that natural selection could not create new species.[32]

Numerous versions of orthogenesis (see table) have been proposed. Debate centred on whether such theories were scientific, or whether orthogenesis was inherently vitalistic or essentially theological.[33] For example, biologists such as Maynard M. Metcalf (1914), John Merle Coulter (1915), David Starr Jordan (1920) and Charles B. Lipman (1922) claimed evidence for orthogenesis in bacteria, fish populations and plants.[34][35][36][37] In 1950, the German paleontologist Otto Schindewolf argued that variation tends to move in a predetermined direction. He believed this was purely mechanistic, denying any kind of vitalism, but that evolution occurs due to a periodic cycle of evolutionary processes dictated by factors internal to the organism.[38][39] In 1964 George Gaylord Simpson argued that orthogenetic theories such as those promulgated by Du Noüy and Sinnott were essentially theology rather than biology.[33]

Though evolution is not progressive, it does sometimes proceed in a linear way, reinforcing characteristics in certain lineages, but such examples are entirely consistent with the modern neo-Darwinian theory of evolution.[40] These examples have sometimes been referred to as orthoselection but are not strictly orthogenetic, and simply appear as linear and constant changes because of environmental and molecular constraints on the direction of change.[41][42] The term orthoselection was first used by Ludwig Hermann Plate, and was incorporated into the modern synthesis by Julian Huxley and Bernard Rensch.[9]

Recent work has supported the mechanism and existence of mutation-biased adaptation, meaning that limited local orthogenesis is now seen as possible.[43][44][45]

A satirical opinion of Ernst Haeckel's 1874 The modern theory of the descent of man, showing a linear sequence of forms leading up to 'Man'. Illustration by G. Avery for Scientific American, 11 March 1876

The stronger versions of the orthogenetic hypothesis began to lose popularity when it became clear that they were inconsistent with the patterns found by paleontologists in the fossil record, which were non-rectilinear (richly branching) with many complications. The hypothesis was abandoned by the mainstream of evolutionists when no mechanism could be found that would account for the process, and the theory of evolution by natural selection came to prevail.[70] The historian of biology Edward J. Larson commented that

At theoretical and philosophical levels, Lamarckism and orthogenesis seemed to solve too many problems to be dismissed out of hand—yet biologists could never reliably document them happening in nature or in the laboratory. Support for both concepts evaporated rapidly once a plausible alternative appeared on the scene.[71]

The modern synthesis of the 1930s and 1940s, in which the genetic mechanisms of evolution were incorporated, appeared to refute the hypothesis for good. As more was understood about these mechanisms it came to be held that there was no naturalistic way in which the newly discovered mechanism of heredity could be far-sighted or have a memory of past trends. Orthogenesis was seen to lie outside the methodological naturalism of the sciences.[72][73][74]

Ernst Mayr considered orthogenesis effectively taboo in 1948.[6]

By 1948, the evolutionary biologist Ernst Mayr, as editor of the journal Evolution, made the use of the term orthogenesis taboo: "It might be well to abstain from use of the word 'orthogenesis' .. since so many of the geneticists seem to be of the opinion that the use of the term implies some supernatural force."[6][7] With the rise of evolutionary developmental biology in the late 20th-early 21st centuries, however, which is open to an expanded concept of heredity that incorporates the physics of self-organization, ideas of constraint and preferred directions of morphological change have made a reappearance in evolutionary theory.[75]

For these and other reasons, belief in evolutionary progress has remained "a persistent heresy",[47] among evolutionary biologists including E. O. Wilson[76] and Simon Conway Morris, although often denied or veiled. The philosopher of biology Michael Ruse wrote that "some of the most significant of today's evolutionists are progressionists, and that because of this we find (absolute) progressionism alive and well in their work."[77] He argued that progressionism has harmed the status of evolutionary biology as a mature, professional science.[78] Presentations of evolution remain characteristically progressionist, with humans at the top of the "Tower of Time" in the Smithsonian Institution in Washington D.C., while Scientific American magazine could illustrate the history of life leading progressively from mammals to dinosaurs to primates and finally man. Ruse noted that at the popular level, progress and evolution are simply synonyms, as they were in the nineteenth century, though confidence in the value of cultural and technological progress has declined.[4]

The frontispiece to Thomas Henry Huxley's 1863 Evidence as to Man's Place in Nature was intended to compare the skeletons of apes and humans, but unintentionally created a durable meme of supposed "monkey-to-man" progress.[79]

In popular culture, progressionist images of evolution are widespread. The historian Jennifer Tucker, writing in The Boston Globe, notes that Thomas Henry Huxley's 1863 illustration comparing the skeletons of apes and humans "has become an iconic and instantly recognizable visual shorthand for evolution."[79] She calls its history extraordinary, saying that it is "one of the most intriguing, and most misleading, drawings in the modern history of science." Nobody, Tucker observes, supposes that the "monkey-to-man" sequence accurately depicts Darwinian evolution. The Origin of Species had only one illustration, a diagram showing that random events create a process of branching evolution, a view that Tucker notes is broadly acceptable to modern biologists. But Huxley's image recalled the great chain of being, implying with the force of a visual image a "logical, evenly paced progression" leading up to Homo sapiens, a view denounced by Stephen Jay Gould in Wonderful Life.[79]

Man is But a Worm by Edward Linley Sambourne, Punch's Almanack for 1882

Popular perception, however, had seized upon the idea of linear progress. Edward Linley Sambourne's Man is But a Worm, drawn for Punch's Almanack, mocked the idea of any evolutionary link between humans and animals, with a sequence from chaos to earthworm to apes, primitive men, a Victorian beau, and Darwin in a pose that according to Tucker recalls Michelangelo's figure of Adam in his fresco adorning the ceiling of the Sistine Chapel. This was followed by a flood of variations on the evolution-as-progress theme, including The New Yorker's 1925 "The Rise and Fall of Man", the sequence running from a chimpanzee to Neanderthal man, Socrates, and finally the lawyer William Jennings Bryan who argued for the anti-evolutionist prosecution in the Scopes Trial on the State of Tennessee law limiting the teaching of evolution. Tucker noted that Rudolph Franz Zallinger's 1965 "The Road to Homo Sapiens" fold-out illustration in F. Clark Howell's Early Man, showing a sequence of 14 walking figures ending with modern man, fitted the palaeoanthropological discoveries "not into a branching Darwinian scheme, but into the framework of the original Huxley diagram." Howell ruefully commented that the "powerful and emotional" graphic had overwhelmed his Darwinian text.[79]

One of many versions of the progressionist meme: Astronomy Evolution 2 artwork by Giuseppe Donatiello, 2016

Scientists, Ruse argues, continue to slide easily from one notion of progress to another: even committed Darwinians like Richard Dawkins embed the idea of cultural progress in a theory of cultural units, memes, that act much like genes.[4] Dawkins can speak of "progressive rather than random ... trends in evolution".[80][81] Dawkins and John Krebs deny the "earlier [Darwinian] prejudice"[82] that there is anything "inherently progressive about evolution",[83][82] but, Ruse argues, the feeling of progress comes from evolutionary arms races which remain in Dawkins's words "by far the most satisfactory explanation for the existence of the advanced and complex machinery that animals and plants possess".[84][82]

Ruse concludes his detailed analysis of the idea of Progress, meaning a progressionist philosophy, in evolutionary biology by stating that evolutionary thought came out of that philosophy. Before Darwin, Ruse argues, evolution was just a pseudoscience; Darwin made it respectable, but "only as popular science". "There it remained frozen, for nearly another hundred years",[4] until mathematicians such as Fisher[85] provided "both models and status", enabling evolutionary biologists to construct the modern synthesis of the 1930s and 1940s. That made biology a professional science, at the price of ejecting the notion of progress. That, Ruse argues, was a significant cost to "people [biologists] still firmly committed to Progress" as a philosophy.[4]