Difference between revisions of "Darwinism" - New World Encyclopedia
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==Theory of natural selection== | ==Theory of natural selection== | ||
| − | The theory of natural selection is one of two major theories advanced by Darwin, the other being the [[Evolution#Theory of descent with modification|theory of descent with modification]]. The theory of descent with modification deals with the pattern of evolution: | + | The [[Evolution#Theory of natural selection|theory of natural selection]] is one of two major [[evolution|evolutionary]] theories advanced by [[Darwin]], the other being the [[Evolution#Theory of descent with modification|theory of descent with modification]]. The theory of descent with modification deals with the pattern of evolution: groups of organisms are related with one another, sharing common ancestors from which they have descended. The theory of natural selection (or "theory of modification through natural selection") deals with the process or mechanism of evolution: how the evolutionary change 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. | + | [[Natural selection]] is the mechanism whereby populations of individuals with favorable traits reproduce more than individuals that lack such beneficial traits, and populations of individuals with deleterious traits reproduce less than individuals without such harmful traits. Over time, this results in a trend toward individuals with traits more 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: | 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 by the ability to produce offspring by finding partners. |
| − | 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 | + | 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. | + | 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, | + | Some scientists, including Darwin, maintain that natural selection only works on the level of the organism. Others, such as [[Stephen Jay Gould|Gould]], believe in hierarchical levels of selection—that natural selection can work both on individuals or groups of individuals, such that some populations or species may have favorable traits that promote their survial and reproduction over other species or populations. Richard Dawkins believed natural selection worked on the level of the [[gene]]. |
| − | + | On the [[microevolution|microevolutionary]] level (change within species), there are evidences that natural selection can produce evolutionary change. For example, changes in gene frequencies can be observed in populations of fruit flies exposed to selective pressures in the laboratory environment. Likewise, systematic changes in various phenotypes within a species, such as color changes in moths, can be observed in field studies. However, evidence that natural selection is the directive force of change in terms of the origination of new designs, such as the development of feathers, or major transitions between higher taxa (such as the evolution of land-dwelling vertebrates from fish) is not observable. Evidence for such [[macroevolution|macroevolutionary]] change is 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 == | == History of the term Darwinism == | ||
| − | In Darwin's day ,there was no rigid definition of the term "Darwinism" | + | In [[Darwin]]'s day ,there was no rigid definition of the term "Darwinism," and it was used by proponents and opponents 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 " | + | 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 [[Lamarck|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- | + | What we now call "[[Social Darwinism]]" was, in its day, synonymous with one use of the word "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. | 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 | + | 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 (Larmarckism) was rejected (Mayr 2001; Gould 2002). At that time, near the end of the 19th century, there was a strong debate between the neo-Larmarckians 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 | + | 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. The modern meaning of neo-Darwinism is not "genealogically linked" to the earlier definition (Gould 2002). |
== Darwinism and other -isms == | == Darwinism and other -isms == | ||
| − | It is felt by some that the term "Darwinism" is sometimes used by [[creationism|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, | + | It is felt by some that the term "Darwinism" is sometimes used by [[creationism|creationists]] as a somewhat derogatory term for "evolutionary biology," in that casting of 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, have used the term repeatedly, without any derogatory connotations. |
==Challenges to Darwinism== | ==Challenges to Darwinism== | ||
Revision as of 21:57, 16 April 2006
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" also has 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 with more modern versions, such as the modern evolutionary synthesis.
According to Ernst Mayr (1991), how the term "Darwinism" has been and is 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." That is, the term should be limited to the philosophical concept of Darwin's theory regarding the mechanism for evolutionary change.
Theory of natural selection
The theory of natural selection is one of two major evolutionary 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: groups of organisms are related with one another, sharing common ancestors from which they have descended. The theory of natural selection (or "theory of modification through natural selection") deals with the process or mechanism of evolution: how the evolutionary change 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 beneficial traits, and populations of individuals with deleterious traits reproduce less than individuals without such harmful traits. Over time, this results in a trend toward individuals with traits more 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 by the ability to produce offspring by finding partners.
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, including Darwin, maintain that natural selection only works on the level of the organism. Others, such as Gould, believe in hierarchical levels of selection—that natural selection can work both on individuals or groups of individuals, such that some populations or species may have favorable traits that promote their survial and reproduction over other species or populations. Richard Dawkins believed natural selection worked on the level of the gene.
On the microevolutionary level (change within species), there are evidences that natural selection can produce evolutionary change. For example, changes in gene frequencies can be observed in populations of fruit flies exposed to selective pressures in the laboratory environment. Likewise, systematic changes in various phenotypes within a species, such as color changes in moths, can be observed in field studies. However, evidence that natural selection is the directive force of change in terms of the origination of new designs, such as the development of feathers, or major transitions between higher taxa (such as the evolution of land-dwelling vertebrates from fish) is not observable. Evidence for such macroevolutionary change is 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 proponents and opponents 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 one use of the word "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 (Larmarckism) was rejected (Mayr 2001; Gould 2002). At that time, near the end of the 19th century, there was a strong debate between the neo-Larmarckians 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. The modern meaning of neo-Darwinism 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 of 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, have used the term repeatedly, without any derogatory connotations.
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.
Evolutionary arguments are often set up against the straw man of Bibilical fundamentalism, in which God created each species separately and the earth is only 6,000 years old. But theistic, teleolgocial explanations of the origin of species may be much more sophistica and aligned with scientific findings.
One challenge is the origin of variability. It is theoretically possible that a divine beings is the origin of the variability, not chance processes. Natural seleciton then acts on the variability. There are also scientists who feel that the importance accorded to genes may be overstated. According to Wells, genetic expression is impacted by morphology as well, such a smembranes and cytoskeletal structure. Thus, for major chances in speciation, itmay be that morphological change is required. Indeed, much genetic change takes place through the mechanism of sexual reproduction and genetic recombination,and many religious adherents consider the sexual act to the the place of God's participation in life.
history one of dogamatism, just like religious fundamentalists.
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