WHAT IS ORTHOGENESIS?

The term orthogenesis (from the Greek ortho meaning straight or linear), autogenesis or progressive evolution, is an idea that gives an intrinsic directionality to the evolutionary process. This concept was coined in 1893 by the German zoologist Wilhelm Haaks, and had its heyday in the first half of the 20th century.

Orthogenesis postulates the existence of an "energy" or internal force of organisms that directs evolution, thus causing a linear pattern. For this reason, the most dogmatic defenders of the theory do not consider the mechanism of natural selection as valid to explain evolutionary change.

Source: Tkgd2007

After the establishment of Darwinian ideas and the development of the synthetic theory of evolution, the theory of orthogenesis was displaced. The role of Sir Ronald Fisher - one of the most notable biologists who was actively involved in the synthesis - was crucial in order to completely abolish this idea.

Although in some lineages the change is apparently linear, the way in which they change is fully compatible with current neo-Darwinian theories.

About two centuries ago, naturalists wondered whether evolution was the product of environmental consequences or whether there were internal forces in organisms that “directed” the evolutionary process.

For many years, theoretical biologists postulated a wide range of innate tendencies or evolutionary laws that affected evolution, making it directional.

The first theories of directed evolution were known under the name "orthogenesis." The term was used to refer to evolutionary changes in specific directions due to limitations in the production of variation. Today, these ideas are being taken up by the novel discipline of evo-devo.

It is necessary to clarify that this theory does not imply that the direction has a defined goal or objective, therefore a religious nuance should not be applied to it. We will discuss this idea in depth later.

Historical perspective

The theory of orthogenesis dates back almost a century and a half. During this time, different researchers raised more than two dozen concepts of "directed evolution", independently.

The term became very popular and gained a large following in the mid-19th century. Renowned biologists such as Theodor Eimer, Bateson and Lamarck himself contributed to its dissemination.

Eimer was the first to define orthogenesis as "the general law by which evolutionary change occurs in a clear direction."

Jean-Baptiste Lamarck, with the inheritance of acquired characters and his first theories of evolution, was related in certain aspects to the theory of orthogenesis, since within the mechanism proposed by Lamarck there was an intrinsic linear component.

The famous German biologist Ernst Haeckel also had evolutionary ideas related to orthogenesis. Unlike Lamarck, Haeckel did not see that the evolutionary process ended in a specific end or goal.

Thanks to the apparent linear pattern that certain groups in the fossil record follow, several renowned paleontologists of the time became enthusiastic about orthogenesis.

Collapse of orthogenesis

The theory of orthogenesis began its decline with the advent of Darwinian principles and with the establishment of evolutionary synthesis.

With increasing evidence within the fossil record, it became clear that very few lineages follow a linear evolutionary pattern.

Although many theorists were defenders of the theory, no one could establish a plausible mechanism that could explain evolutionary change. When evolutionary synthesis posited robust genetic mechanisms, the hypothesis was discarded.

Some biologists who chose to take anti-Darwinian positions continued with orthogenesis as an alternative theory - along with saltationism and Lamarckism or Neo Lamarckism. However, the evidence failed to support them.

Cooptation of the term

While it is clear that the theory of directed evolution was in vogue for an extended period, the use of the term orthogenesis became problematic and confusing in the literature.

For example, Julian Huxley divided orthogenesis into two categories: dominant and secondary. Stephen Jay Gould, for his part, proposes a distinction between Swabian and Hard orthogenesis, both with different meanings that were initially proposed.

For Gould, hard orthogenesis encompasses the idea of the predetermined extinction and aging of a taxon. For this reason, it must be made clear that each author gives a new nuance - and sometimes a totally new meaning - to orthogenesis.

Modern vision

Evolution is not linear

Currently, when we think about evolution, almost instantaneously a linear image of progressive scale comes to mind, which can be represented by an ascending row of ancestral hominids, such as Australopithecines and Neanderthals, ending at the "pinnacle" of nature: the current human.

The image can also showcase modern species in a row, from fish to amphibians and reptiles to humans or other mammals.

Both representations, widely disseminated by the media, misrepresent what evolutionary mechanisms represent as they are understood today. In fact, this concept delays a few centuries, the advance that evolutionary biologists have made thus far.

The first mistake of these hierarchical chains is to expect to find forms of connection or missing links between the current species. The current human did not "evolve" from the current chimpanzee; both species share a recent common ancestor.

The second mistake is to represent evolution as a process with a definite goal. Evolution is a process that advances blindly, where there is no talk of progress or an end goal. As we mentioned, orthogenesis does not directly propose the existence of a goal, but it is necessary to clarify this point.

Evolution advances blindly

Returning to this phrase, evolution has no way of predicting the future to create improvements. Imagine a population of rabbits experiencing a frost.

By decreasing temperatures, rabbits with thicker fur - the product of a random mutation - will contribute more individuals to the next generation, thus varying the allele frequencies of the population.

However, rabbits do not have the ability to predict frost to generate mutations that give them a more abundant coat.

References

Darwin, C. (1859). On the origins of species by means of natural selection. Murray.
Freeman, S., & Herron, JC (2002). Evolutionary analysis. Prentice Hall.
Futuyma, DJ (2005). Evolution. Sinauer.
Grehan, JR, & Ainsworth, R. (1985). Orthogenesis and evolution. Systematic Zoology, 34 (2), 174-192.
Popov, I. (2018). Orthogenesis versus Darwinism. Springer.
Rice, S. (2007). Encyclopedia of Evolution. Facts on File.
Russell, P., Hertz, P., & McMillan, B. (2013). Biology: The Dynamic Science. Nelson Education.
Soler, M. (2002). Evolution: the basis of Biology. South Project.
Wissemann, V. (2006). Annals of the History and Philosophy of Biology 11/2006. Universitätsverlag Göttingen.

WHAT IS ORTHOGENESIS? - BIOLOGY - 2026