Darwinism
Darwinism is a term that is generally considered synonymous with the theory of natural selection. This theory, which was developed by Charles Darwin, holds that natural selection is the directive or creative force of evolution.
The term "Darwinism" has also been applied to the evolutionary theories of Charles Darwin in general, rather than just the theory of natural selection. It may also refer specifically to the role of Charles Darwin as opposed to others in the history of evolutionary thought — particularly contrasting Darwin's results with those of earlier theories such as Lamarckism or later ones such as the modern synthesis.
According to Mayr (1991), how the term has been used depends on who is using it and the time period. On the other hand, Harvard evolutionist Stephen Jay Gould, himself a popular writer on evolution, maintains that although the popular literature often equates Darwinism with evolution itself, the scientific community generally agrees that the term "should be restricted to the worldview encompassed by the theory of natural selection itself." That is, the term should be limited to the philosophical concept of Darwin's theory of mechanism for evolutionary change.
Theory of natural selection
The theory of natural selection is one of two major theories advanced by Darwin, the other being the theory of descent with modification. The theory of descent with modification deals with the pattern of evolution: that groups of organisms descended from common ancestors, with descendant species being modified from each other in some manner over time. The theory of natural selection (or "theory of modification through natural selection") deals with the process or mechanism of evolution: how the evolution occured in order to arrive at the pattern.
Natural selection is the mechanism whereby populations of individuals with favorable traits reproduce more than individuals that lack such traits, and populations of individuals with deleterious traits reproduce less than individuals without such traits. Over time, this results in a trend toward individuals with traits conducive to their survival and reproduction. According to this theory, natural selection is the directive or creative force of evolution, creating new species and new designs, rather than just a force for weeding out unfit organisms.
In a modern definition of the term, a Darwinian process requires the following schema:
- Self-replication/Inheritance: Some number of entities must be capable of producing copies of themselves, and those copies must also be capable of reproduction. The new copies must inherit the traits of old ones. Sometimes the different variations are recombined in sexual reproduction.
- Variation: There must be a range of different traits in the population of entities, and there must be a mechanism for introducing new variations into the population.
- Selection: Inherited traits must somehow affect the ability of the entities to reproduce themselves, either by survival, or natural selection, or by ability to produce offspring by finding partners, or sexual selection.
If the entity or organism survives to reproduce, the process restarts. Sometimes, in stricter formulations, it is required that variation and selection act on different entities, variation on the replicator (genotype) and selection on the interactor (phenotype).
Darwinism asserts that any system given these conditions, by whatever means, evolution is likely to occur. That is, over time, the entities will accumulate complex traits that favor their reproduction. This is called Universal Darwinism, a term coined by Richard Dawkins in his 1972 book Selfish Gene.
Some scientists, such as Darwin, maintain that natural selection only works on the level of the organisms. Others, such as Gould, believe in hierarchical levels of selection—that natural selection can work on individuals, populations, species, etc. Richard Dawkins believed it worked on the level of the gene.
Evidence for the theory of modification by natural selection on the level at or below the level of species (microevolution) is readily apparent. It can be seen in populations changes in fruit flies in the laboratory or change in color of moths in the field. However, evidence that natural selection is the directive force of change in terms of the origination of new designs or major transitions between higher taxa (macroevolution) is not observable and is necessarily limited to extrapolation from changes on the microevolutionary level. A number of top evolutionists, including Gould, challenge the validity of making such extrapolations.
History of the term Darwinism
In Darwin's day ,there was no rigid definition of the term "Darwinism", and it was used by opponents and proponents of Darwin's biological theory alike to mean whatever they wanted it to in a larger context. In the 19th-century context in which Darwin's Origin of Species was first received, "Darwinism" came to stand for an entire range of evolutionary (and often revolutionary) philosophies about both biology and society.
One of the more prominent approaches was that summed in the phrase "survival of the fittest" by the philosopher Herbert Spencer. This was later taken to be emblematic of Darwinism, even though Spencer's own understanding of evolution was more Lamarckian than Darwinian, and predated the publication of Darwin's theory.
What we now call "Social Darwinism" was, in its day, synonymous with "Darwinism"—the application of Darwinian principles of "struggle" to society, usually in support of anti-philanthropic political agendas. Another interpretation, one notably favored by Darwin's cousin Francis Galton, was that Darwinism implied that because natural selection was apparently no longer working on "civilized" people it was possible for "inferior" strains of people (who would normally be filtered out of the gene pool) to overwhelm the "superior" strains, and corrective measures would have to be undertaken — the foundation of eugenics.
Many of the ideas called "Darwinism" had only a rough resemblance to the theory of Charles Darwin. For example, Ernst Haeckel developed what was known as Darwinismus in Germany; though it should be noted that his ideas was not centered around natural selection at all.
To distinguish themselves from the very loose meaning of "Darwinism" prevalent in the 19th century, those who advocated evolution by natural selection after the death of Darwin became known as neo-Darwinists. The term "neodarwinism" itself was coined by George John Romanes in 1896 to designate the Darwinism proposed by August Weismann and Alfred Russel Wallace, in which the exclusivity of natural selection was promoted and the inheritance of acquired characteristics is rejected (Mayr 2001; Gould 2002). At that time, near the end of the 19th century, there was a strong debate between the neo-Larmarkians and the neo-Darwinians.
The term neo-Darwinism was not terribly popular in the scientific community until after the development of the modern evolutionary synthesis in the 1930s, when the term became synonomyous with the synthesis of the 1930's and since. The modern meaning is not "genealogically linked" to the earlier definition (Gould 2002).
Darwinism and other -isms
It is felt by some that the term "Darwinism" is sometimes used by creationists as a somewhat derogatory term for "evolutionary biology," in that casting evolution as an "ism"—a doctrine or belief —strengthens calls for "equal time" for other beliefs such as creationism. However, top evolutionary scientists, such as Gould and Mayr, has used the term repeatedly, with no such derogatory connoations.
Challenges to Darwinism
IN addition to the lack of evidence for natural seleciton as the causal agent on macroevolutionary levels, as noted above, there are challenges to the theory of natural selection itslef. These come from both the scientific and religious communities. This is not a new development. Unlike the theory of descent with modification, which was accepted by the scientific community during Darwin's time and for which substantial evidences have been marshalled, the theory of natural seleciton was not widely accepted until the mid-1900s, and remains controversial even today.
Many of these relate to religious viewpoitns. In particular, those advocating design by a creator God do not accept that new designs could come about by chance. And chance (stochastic processes) are involved in the theory of natural selection. As noted by eminient evolutionist Ernst Mayr (2001), chance plays an important part in two steps. First, the production of genetic variation "is almost exlusively a chance phenomena." Secondly, chance plays an important roele even in "the process of the elimination of less fit individuals," and partiuclar during periods of mass extinction.
Other challenges include:
- 1. origin of variability.
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
