Orthogenesis

Definition

Orthogenesis was a term first used by the biologist Wilhelm Haacke in 1893. Theodor Eimer was the first to give the word a definition; he defined orthogenesis as "the general law according to which evolutionary development takes place in a noticeable direction, above all in specialized groups."

In 1922, the zoologist Michael F. Guyer wrote:

[Orthogenesis] has meant many different things to many different people, ranging from a, mystical inner perfecting principle, to merely a general trend in development due to the natural constitutional restrictions of the germinal materials, or to the physical limitations imposed by a narrow environment. In most modern statements of the theory, the idea of continuous and progressive change in one or more characters, due according to some to internal factors, according to others to external causes-evolution in a "straight line" seems to be the central idea.

Orthogenesis was often related to neo-Lamarckism; Eimer popularized the concept of orthogenesis in his book Organic Evolution as the Result of the Inheritance of Acquired Characteristics According to the Laws of Organic Growth (1890). In his work Eimer 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. To orthogenesis trends in evolution were often nonadaptive and in some cases species could be led to extinction.

Peter J. Bowler has defined orthogenesis as:

Literally, the term means evolution in a straight line, generally assumed to be evolution that is held to a regular course by forces internal to the organism. Orthogenesis assumes that variation is not random but is directed towards fixed goals. Selection is thus powerless, and the species is carried automatically in the direction marked out by internal factors controlling variation.

According to (Schrepfer, 1983):

Orthogenesis meant literally "straight origins", or "straight line evolution". The term varied in meaning from the overtly vitalistic and theological to the mechanical. It ranged from theories of mystical forces to mere descriptions of a general trend in development due to natural limitations of either the germinal material or the environment... By 1910, however most who subscribed to orthogenesis hypothesized some physical rather than metaphysical determinant of orderly change.

Orthogenesis has been described as an "anti-Darwinian" evolutionary theory because of its stance on the Darwinian mechanism of natural selection. After studying butterfly coloration Theodor Eimer published a widely read book on orthogenesis titled On Orthogenesis: And the Impotence of Natural Selection in Species Formation (1898). In the book Eimer claimed there were trends in evolution with no adaptive significance and thus would be difficult to explain by natural selection. Stephen Jay Gould wrote a detailed biography of Eimer. Gould wrote that Eimer was a materialist who rejected any vitalist or teleological approach to orthogenesis and explained that Eimer's criticism of natural selection was common amongst many evolutionists of his generation as they were searching for alternative evolutionary mechanisms as it was believed at the time that natural selection could not create new species.

Origins

The orthogenesis hypothesis had a significant following in the 19th century when a number of evolutionary mechanisms, such as Lamarckism, were being proposed. Jean-Baptiste Lamarck 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. 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. In fact, Darwin himself rarely used the term "evolution" now so commonly used to describe his theory, because in Darwin's time, evolution usually was associated with some sort of progressive process like orthogenesis, and this had been common usage since at least 1647.

Theories

An early theory of orthogenesis was the "inner perfecting principle" of Carl Nägeli. According to Nageli many evolutionary developments were nonadaptive and variation was internally programmed. The Russian biologist Lev Berg developed his own theory of orthogenesis known as nomogenesis. Albert von Kölliker's orthogenetic theory was known as heterogenesis. The paleontologist Henry Fairfield Osborn also supported a theory of orthogenesis known as aristogenesis. Italian zoologist Daniele Rosa proposed the theory hologenesis.

Scientists such as Metcalf (1914), Coulter (1915), Jordan (1920) and Lipman (1922) claimed evidence for orthogenesis in bacteria, fish populations and plants. The zoologist Charles Otis Whitman was an advocate of orthogenesis and rejected Lamarckism, Darwinism and mutationism. Whitman only wrote one book on orthogenesis, which was published nine years after his death in 1919. Titled Orthogenetic Evolution in Pigeons, the book was published in a three volume set titled Posthumous Works of Charles Otis Whitman. It was described as written too late to win any major influence.

In 1930, the American zoologist Austin Hobart Clark attempted to modify orthogenesis with his theory of zoogenesis.

Karl Beurlen invented the term palingenesis as a mechanism for his orthogenetic theory of evolution. In the 1950s the German paleontologist Otto Schindewolf developed a theory of orthogenesis, which claimed that variation tends to move in a predetermined direction. His theory became known as typostrophism and stated that evolution occurs due to a periodic cyclic model of evolutionary processes which are predestined to go through a life cycle dictated by factors internal to the organism.

Teleological

Most theories of orthogenesis were not teleological. According to Stephen Jay Gould "most leading orthogeneticists held strictly mechanistic views". Gould compared the minority proponents of teleological orthogenesis to theistic evolution.

The Russian biologist Karl Ernst von Baer had believed in a teleological force in nature which has been compared to a form of orthogenesis.

The philosopher Henri Bergson linked orthogenesis with vitalism by a creative force in evolution known as élan vital in his book Creative Evolution (1907).

Pierre Lecomte du Noüy developed a teleological version of orthogenesis known as telefinalism. Similar views were also held by Edmund Ware Sinnott with his concept of Telism. Such views were heavily criticized as non-scientific. George Gaylord Simpson claimed that Du Noüy and Sinnott were promoting a theological version of orthogenesis and their arguments were essentially religious.

Another form of teleological orthogenesis was developed by Pierre Teilhard de Chardin, a Jesuit paleontologist, in The Phenomenon of Man (a book influential among non-scientists that was published four years after his death in 1959) argued for evolution aiming for the "Omega Point", while putting man at the center of the universe and accounting for original sin. The term Chardin used for this was "directed additivity".

Collapse of the hypothesis

The orthogenesis hypothesis began to collapse when it became clear that it could not explain the patterns found by paleontologists in the fossil record, which was non-linear with many complications. The hypothesis was generally abandoned when no mechanism could be found that would account for the process, and the theory of evolution by natural selection became the prevailing theory of evolution.

The modern evolutionary synthesis, in which the genetic mechanisms of evolution were discovered, refuted the hypothesis for good. As more was understood about these mechanisms it became apparent that there was no possible naturalistic way in which the newly discovered mechanism of heredity could be far-sighted or have a memory of past trends. Thus it fell outside the purview of the methodological naturalism of the sciences.

The orthogenetic hypothesis, however, died hard. Even Darwin was at first not opposed to orthogenic thinking, as this quote from the 1911 Encyclopædia Britannica demonstrates:

The refutation of orthogenesis had some ramifications in the field of philosophy, as it questioned the idea of teleology or existence of immutable "forms" in nature, as first developed by Aristotle and accepted by Immanuel Kant, who had greatly influenced many scientists. Before the scientific and philosophical revolution that began with Charles Darwin's work, the prevailing philosophy was that the world was teleological and purposeful, and that science was the study of God's creation. The interpretation of evolutionary mechanisms (which of themselves assert neither necessary progression nor finality) as supporting a naturalistic worldview has led to a shift in what science and scientists are perceived to be.

Modern co-opted usage

Though linear, progressive evolution has been refuted, it is not true that evolution never proceeds in a linear way, reinforcing characteristics, in certain lineages at times, for example, during a period of slow, sustained environmental change, but such examples are entirely consistent with the modern neo-Darwinian theory of evolution.

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. The term orthoselection was first used by Ludwig Hermann Plate, and was incorporated into the modern evolutionary synthesis by Julian Huxley and Bernard Rensch.