Misplaced Pages

Revision as of 13:56, 15 June 2005

The history of evolutionary thought has a long history since the idea of biological evolution has existed since ancient times, but the modern theory wasn't established until the 18th and 19th centuries, with scientists such as Jean-Baptiste Lamarck and Charles Darwin. Darwin greatly emphasized the difference between his two main points: establishing the fact of evolution, and proposing the theory of natural selection to explain the mechanism of evolution.

From ancient times to 1850s

See also History of creationism and Evolutionism.

The idea of biological evolution was supported in ancient times, notably among Hellenists such as Democritus and his student Epicurus. As early as 400 BC the Greek atomists taught that the sun, earth, life, humans, civilization, and society emerged over aeons without divine intervention. Around 60 BC the Roman atomist Lucretius wrote the poem On the Nature of Things describing the development of the living earth in stages from atoms colliding in the void as swirls of dust, then early plants and animals springing from the early earth's substance, to a succession of animals including a series of progressively less brutish humans.

In 17th century English the word evolution (from the Latin word "evolutio", meaning "unroll like a scroll") began to be used in to refer to an orderly sequence of events, particularly one in which the outcome was somehow contained within it from the start. In 1677 Sir Matthew Hale used the term evolution in attacking the atheistic atomism of Democritus and Epicurus. Hale set out the atomist idea that vibrations and collisions of atoms in the void without divine intervention had formed "Primordial Seeds" (semina) which were the "immediate, primitive, productive Principles of Men, Animals, Birds and Fishes." and called this mechanism an "absurdity" because "it must have potentially at least the whole Systeme of Humane Nature, or at least that Ideal Principle or Configuration thereof, in the evolution whereof the complement and formation of the Humane Nature must consist. . . and all this drawn from a fortuitous coalition of senseless and dead Atoms." Thus in evolutionism theories from 1700 to 1850 the earth, life, and universe developed without divine intervention.

Typically of these theories, Gottfried Leibniz in 1714 postulated "monads" inside objects causing motion by internal forces, and maintained that "the 'germs' of all things have always existed . . . contain within themselves an internal principle of development which drives them on through a vast series of metamorphoses" to become the geological formations, lifeforms, psychologies, and civilizations of the present.

In his "Venus Physique" of 1745, Pierre Louis Maupertuis wrote of "Chance" producing "an innumerable multitude of individuals" a small number of which had "fitness" to satisfy their needs, while "another infinitely greater number... perished... The species we see today are but the smallest part of what blind destiny has produced...", anticipating in general terms the idea of natural selection.

Charles Bonnet applied "Evolutionism" to biology in 1762, asserting that each feature of the embryo was preformed in the parts; some of which came from the egg and some from the sperm. The preformed parts expanded and rearranged themselves to grow into the adult, and so Bonnet was called a "preformationist." James Hutton's theory of 1785 said that the Earth must be much older than previously supposed, to allow time for mountains to be eroded and for sediment to form new rocks at the bottom of the sea, which in turn rose to become dry land.

Acquired characteristics, Lamarckism, and natural selection

Between 1794 and 1796 Erasmus Darwin wrote Zoönomia suggesting "that all warm-blooded animals have arisen from one living filament... with the power of acquiring new parts" in response to stimuli, with each round of "improvements" being inherited by successive generations. In his "Temple of Nature." of 1802 he described recurring new earths appearing in a cycle of catastrophes, then life springing forth spontaneously to populate the new earth, with animals competing with each other, driven by sex, hunger, "the strongest and most active.. propagate the species, which should thence become improved.":

Jean-Baptiste Lamarck proposed in his Philosophie Zoologique of 1809 a theory, later known as Lamarckism, by which traits that were "needed" were acquired (or diminished) during the lifetime of an organism then passed on to the offspring. Lamarck avoided the word "evolution" as he was describing acquired traits, while popular notions of "evolution" at the time asserted Bonnet's "preformationist" idea that the parent passed on the "germs" given by the grandparents unaltered by the parent's "learning".

William Smith began the process of ordering rock strata by examining fossils in the layers. Independently, Georges Cuvier and Alexandre Brongniart published their explanation of the antiquity of the Earth in 1811 on the principle of stratigraphic succession of the layers of the earth, but rejected evolution in favour of catastrophism.

In 1813, William Charles Wells produced essays assuming that there had been evolution of humans, and recognised the principle of natural selection. Charles Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them. Augustin de Candolle's natural system of classification laid emphasis on the "war" between competing species.

A radical British school of comparative anatomy which included the surgeon Robert Knox and the anatomist Robert Edmund Grant was closely in touch with Lamarck's school of French Transformationism, which included Étienne Geoffroy Saint-Hilaire. Grant developed Lamack's and Erasmus Darwin's ideas of transmutation and evolutionism, investigating homology to prove common descent. As a young student Charles Darwin joined Grant in investigations of the life cycle of marine animals. He also studied geology under professor Robert Jameson who wrote an anonymous paper in 1826 praising "Mr. Lamarck" for explaining how the higher animals had "evolved" from the "simplest worms" – this was the first use of the word "evolved" in a modern sense. Jameson's course closed with lectures on the "Origin of the Species of Animals"

Patrick Matthew wrote in Naval Timber & Arboriculture published in 1831 of "continual balancing of life to circumstance . . . progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction." Charles Darwin found out about it after publication of the Origin, and wrote that it "briefly but completely anticipates the theory of Nat. Selection.... a complete but not developed anticipation!"

By 1833 the geologist Charles Lyell in the second volume of his Principles of Geology had set out a gradualist variation of creation beliefs in which each species had its "centre of creation" and was designed for the habitat, but would go extinct when the habitat changed. John Herschel supported this gradualist view and wrote to Lyell urging a search for natural laws underlying the "mystery of mysteries" of how species formed.

The computing pioneer Charles Babbage published his unofficial Ninth Bridgewater Treatise in 1837, putting forward the thesis that God had the omnipotence and foresight to create as a divine legislator, making laws (or programs) which then produced species at the appropriate times, rather than continually interfering with ad hoc miracles each time a new species was required.

By 1836 the anatomist Richard Owen had theories influenced by Johannes Peter Müller that living matter had an "organising energy", a life-force that directed the growth of tissues and also determined the lifespan of the individual and of the species. In the 1850s Owen developed ideas of "archetypes" in the Divine mind producing a sequence of species in "ordained continuous becoming" in which new species appeared at birth, not through natural selection

In 1837 Charles Darwin started the first of a series of secret notebooks on transmutation. In 1838 he read the new 6th edition of Malthus's Essay on the Principle of Population and compared this with breeders selecting traits. This led to the inception of Darwin's theory, and the publication of Darwin's theory jointly with Wallace in 1858.

Later discrediting of Lamarckism and Orthogenesis

Lamarckism became discredited as experiments simply did not support the concept that purely "acquired traits" were inherited. The mechanisms of inheritance and the notion of the Weismann barrier were not elucidated until later in the 19th century, after Lamarck's death. Lamarckism in toto has largely been discredited as a mechanism in evolution, although some scientists such as Eva Jablonka and colleagues have claimed that certain forms of epigenetic inheritance such as chromatin marking and DNA methylation may involve a form of "soft" Larmarckian evolution, although these claims are controversial. Some have also proposed that Lamarckian evolution may be accurately applied to cultural evolution.

Orthogenesis or orthogenetic evolution was the hypothesis that life has an innate tendency to move, in a unilinear fashion, to ever greater perfection. This hypothesis had a significant following in the 19th century and Lamarck himself accepted the idea, where it had a central role in his theory of inheritance of acquired characteristics. Other proponents included Leo Berg, Henri Bergson and, for a time, the paleontologist Henry Fairfield Osborn. Orthogenesis was particularly accepted by paleontologists who believed that fossils indicated a gradual and constant unidirectional change. Those who accepted orthogenesis in this way, however, did not necessarily accept that the mechanism that drove orthogenesis was teleological (goal-directed).

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. A few hung on to the orthogenesis hypothesis as late as the 1950s by claiming that the processes of macroevolution, the long term trends in evolution, were distinct from the processes of microevolution.

1850s - early 20th century: Darwin's theory

Main articles: Inception of Darwin's theory, Development of Darwin's theory, Publication of Darwin's theory, Reaction to Darwin's theory

While transmutation of species was accepted by a sizeable number of scientists before 1859, it was the publication of Charles Darwin's The Origin of Species which provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection. Darwin was motivated to publish his work on evolution after receiving a letter from Alfred Russel Wallace, in which Wallace revealed his own discovery of natural selection. As such, Wallace is sometimes given shared credit for the theory of evolution. However, Wallace himself backed away from claiming too much credit, admitting that Darwin's formulation of the theory and his work on evolution went far beyond Wallace's conjectures in scope and explanatory power (he would later, to Darwin's great disappointment, back away completely from the idea that humans were evolved by natural means as he began to turn towards spiritualism).

Wilkins identifies Darwin's into seven categories:

1. Transmutationism
2. Common descent
3. Struggle for existence
4. Natural selection
5. Sexual selection
6. Biogeographic distribution
7. Heredity

Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life (and indeed resulted in a small social revolution), could not explain several critical components of the evolutionary process. Namely, he was unable to explain the source of variation in traits within a species, and he could not provide a mechanism whereby traits were passed faithfully from one generation to the next. Darwin's theory of pangenesis, while relying in part on the inheritance of acquired characteristics, proved to be useful for statistical models of evolution developed by his cousin Francis Galton and the "biometric" school of evolutionary thought. It was, however, found to be of little use to biologists.

While the scientific community generally accepted that evolution had occurred, many disagreed that it had happened under the conditions or mechanisms provided by Darwin. In the years immediately following Darwin's death, evolutionary thought fractured into a number of interpretations, include neo-Darwinism, neo-Larmarckism, orthogenesis, Mendelism, the biometric approach, and mutation theory. Eventually this boiled down to a debate between the Mendelians (discrete variation) and the biometricians (continuous variation), which were assembled into the modern evolutionary synthesis by the 1930s.

1920s-1940s: the modern evolutionary synthesis

Main article: Modern evolutionary synthesis

These questions of interpretation were not settled until the early 20th century, beginning with the work of an Austrian monk named Gregor Mendel in the late 19th century, who outlined, through a series of ingeniously devised experiments, a model for inheritance of traits based on the fundamental unit of the gene. Mendel's work was unappreciated at the time and largely ignored by the biological community. When it was "rediscovered" in 1900, it led to a storm of conflict between Mendelians (Charles Benedict Davenport) and biometricians (Walter Frank Raphael Weldon and Karl Pearson), who insisted that the great majority of traits important to evolution must show continuous variation that was not explainable by Mendelian analysis.

Eventually, the two models were reconciled and merged, primarily through the work of the biologist and statistician R.A. Fisher. This combined approach, applying a rigorous statistical model to Mendel's theories of inheritance via genes, became known in the 1930s and 1940s as the modern synthesis of Darwin's theory.

1940s-1960s: developments following molecular biology

In the 1940s, following up on Griffith's experiment, Avery, McCleod and McCarty definitively identified deoxyribonucleic acid (DNA) as the "transforming principle" responsible for transmitting genetic information. In 1953, Francis Crick and James Watson published their famous paper on the structure of DNA, based on the research of Rosalind Franklin and Maurice Wilkins. These developments ignited the era of molecular biology and transformed the understanding of evolution into a molecular process: the mutation of segments of DNA.

During this era of molecular biology, it also became clear that a major mechanism for variation within a population is the mutagenesis of DNA. In the mid-1970s, Motoo Kimura formulated the neutral theory of molecular evolution, firmly establishing the importance of genetic drift as a major mechanism of evolution.

1960s-1980s: Williams revolution, punctuated equilibrium

Coined after the evolutionary biologist, George C. Williams, the Williams revolution is a paradigm shift which occurred in evolutionary biology in the mid-1960s in which verbal arguments, couched in terms of "survival of the species" (essentially group selection arguments) were largely replaced by a gene-centered view of evolution, epitomised by kin selection. Models of the period showed that group selection was severely limited in its strength, although these models have since been shown to be too limited and newer models do admit the possibility of significant multi-level selection.

Other debates have continued within the field. One of the most prominent outstanding debates is over the theory of punctuated equilibrium, a theory propounded by Niles Eldredge and Stephen Jay Gould to explain the paucity of transitional forms between phyla.

1970s-2000s: evolutionary biology as a discipline

Evolutionary biology as an academic discipline in its own right emerged as a result of the modern evolutionary synthesis in the 1930s and 1940s. It was not until the 1970s and 1980s, however, that a significant number of universities had departments that specifically included the term evolutionary biology in their titles. In the United States, as a result of the rapid growth of molecular and cell biology, many universities have split (or aggregated) their biology departments into molecular and cell biology-style departments and ecology and evolutionary biology-style departments (which often have subsumed older departments in paleontology, zoology and the like).

Microbiology has recently developed into an evolutionary discipline. It was originally ignored due to the paucity of morphological traits and the lack of a species concept in microbiology. Now, evolutionary researchers are taking advantage our extensive understanding of microbial physiology, the ease of microbial genomics, and the quick generation time of some microbes to answer evolutionary questions. Similar features have led to progress in viral evolution, particularly for bacteriophage.

Recent developments in evolutionary theory

Daniel Dennett (1995) argues in Darwin's Dangerous Idea that natural selection is an algorithmic process applicable to many circumstances besides biological evolution. This conception of evolutionary has been dubbed "universal Darwinism".

Symbiogenesis

Main article: Symbiogenesis

Another extension to the standard modern synthesis, advocated by Lynn Margulis, is symbiogenesis. Symbiogenesis argues that acquisition and accumulation of random mutations or genetic drift are not sufficient to explain how new inherited variations occur in evolution. This theory states that species arise from the merger of independent organisms through symbiosis. Symbiogenesis emphasizes the impact of co-operation rather than Darwinian competition. This commonly occurs in multigenomic organisms throughout nature.

Neo-structuralist themes in evolutionary theory

In the 1980s and 1990s there was a renewal of structuralist themes in evolutionary biology by biologists such as Brian Goodwin, that incorporates ideas from cybernetics and systems theory, and that emphasizes the role of self-organized processes as being at least as important as the role of natural selection. Some extreme variants consider natural selection as the result of biological evolution and not its cause, though most neo-structuralist biologists would not go this far.

The evolution of altruism

Main article: Altruism

Altruism has been one of the last (and most deeply embedded) thorns in the side of evolutionary theory, but recent developments in game theory have suggested explanations with an evolutionary context. If humans evolved, then so did human minds, and if minds evolved, then so does behaviour - including, according to these models, altruistic tendencies.

Theories of eusociality and the undoubted advantages of kin selection have made good progress in this direction, but they are far from unproblematic. Some writers have pointed out that the conscience is just another aspect of our mental behaviour, and propose an evolutionary explanation for the existence of conscience and therefore altruism. One recent suggestion, expressed most eloquently by the philosopher Daniel Dennett, was initially developed when considering the problem of so-called 'free riders' in the tragedy of the commons, a larger-scale version of the Prisoner's Dilemma.

An interesting example of altruism is found in the cellular slime moulds, such as Dictyostelium mucoroides. These protists live as individual amoebae until starved, at which point they aggregate and form a multicellular fruiting body in which some cells sacrifice themselves to promote the survival of other cells in the fruiting body.

Unconventional extensions to evolutionary ideas

De Chardin's and Huxley's theories

Pierre Teilhard de Chardin and Julian Huxley formulated theories describing the gradual development of the Universe from subatomic particles to human society, considered by Teilhard as the last stage. (see Gaia theory). These are not generally recognized as scientifically rigorous.

Nine levels of development are described in their scheme. Stages one through five are grouped into the Lithosphere, also called Geosphere or Physiosphere, where the evolution of the structure of organisms is ruled by mechanical laws and coincidence. Levels six, seven, and eight are the classical biological stages. Stages six through eight are collectively called the Biosphere, where the progress of the structure of the organisms is ruled by genetic mechanisms. The actual stage, stage 9, is called the Noosphere, where the structure of human society is ruled by psychological, informational and communicative processes.

References

• Peter J. Bowler, Evolution: The history of an idea, Revised Edition (Berkeley, CA: University of California Press, 1989).

See also

• The Voyage of the Beagle
• Galápagos Islands

External links

• Darwin's precursors and infulences by John Wilkins. Part of the Talk.Origins Archive.

• History of evolutionary biology