拉馬克主義

is a theory put forward by the French biologist Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, based on heritability of acquired characteristics, the once widely accepted idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring.

It proposed that individual efforts during the lifetime of the organisms were the main mechanism driving species to adaptation, as they supposedly would acquire adaptative changes and pass them on to offspring. After publication of Charles Darwin's theory of natural selection, the importance of individual efforts in the generation of adaptation was considerably diminished. Later, Mendelian genetics supplanted the notion of inheritance of acquired traits, eventually leading to the development of the modern evolutionary synthesis, and the general abandonment of the Lamarckian theory of evolution in biology. In a wider context, Lamarckism is of use when examining the evolution of cultures and ideas, and is related to the theory of Memetics.

While enormously popular during the early 19th century as an explanation for the complexity observed in living systems, Lamarckism's acceptance within the scientific community dwindled following the dawn of the Darwinian synthesis, currently universally accepted as an explanation for the adaptive complexity of all life forms.

[编辑] History

Jean-Baptiste Lamarck

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. Subsequently Jean-Baptiste Lamarck proposed in his Philosophie Zoologique of 1809 the theory that characteristics which were "needed" were acquired (or diminished) during the lifetime of an organism then passed on to the offspring. He saw this resulting in the development of species in a progressive chain of development towards higher forms.

Lamarck founded a school of French Transformationism which included Étienne Geoffroy Saint-Hilaire, and which corresponded with a radical British school of comparative anatomy based at the University of Edinburgh which included the surgeon Robert Knox and the anatomist Robert Edmund Grant. Professor Robert Jameson 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. As a young student Charles Darwin was tutored by Grant, and worked with him on marine creatures.

The Vestiges of the Natural History of Creation, authored by Robert Chambers and published anonymously in England in 1844, proposed a theory modelled after Lamarckism, causing political controversy for its radicalism and unorthodoxy, but exciting popular interest and paving the way for Darwin.

Darwin's Origin of Species proposed natural selection as the main mechanism for development of species, but did not rule out a variant of Lamarckism as a supplementary mechanism. With the development of the modern synthesis of the theory of evolution and a lack of evidence for heritable acquired characteristics, Lamarckism fell from favour.

In the 1920s, experiments by Paul Kammerer on amphibians, particularly the midwife toad, appeared to find evidence supporting Lamarckism, but were discredited as having been falsified. In The Case of the Midwife Toad Arthur Koestler surmised that the specimens had been faked by a Nazi sympathiser to discredit Kammerer for his political views.

A form of Lamarckism was revived in the Soviet Union of the 1930s when Trofim Lysenko promoted Lysenkoism which suited the ideological opposition of Joseph Stalin to Genetics. This unscientific agricultural policy was later blamed for crop failures.

Since 1988 certain scientists have produced work proposing that Lamarckism could apply to single celled organisms. The discredited belief that Lamarckism holds for higher order animals is still clung to in certain branches of new-age pseudoscience under the term racial memory.

[编辑] Lamarck's theory

The evolution of giraffe necks is often used as the example in explanations of Lamarckism.

Lamarck based his theory on two observations, in his day considered to be generally true:

1. Use and disuse – Individuals lose characteristics they do not require (or use) and develop characteristics that are useful.
2. Inheritance of acquired traits – Individuals inherit the traits of their ancestors.

Examples of Lamarckism would include:

• Giraffes stretching their necks to reach leaves high in trees (especially Acacias), strengthen and gradually lengthen their necks. These giraffes have offspring with slightly longer necks (also known as "soft inheritance").
• A blacksmith, through his work, strengthens the muscles in his arms. His sons will have similar muscular development when they mature.

With this in mind, Lamarck developed two laws:

1. In every animal which has not passed the limit of its development, a more frequent and continuous use of any organ gradually strengthens, develops and enlarges that organ, and gives it a power proportional to the length of time it has been so used; while the permanent disuse of any organ imperceptibly weakens and deteriorates it, and progressively diminishes its functional capacity, until it finally disappears.
2. All the acquisitions or losses wrought by nature on individuals, through the influence of the environment in which their race has long been placed, and hence through the influence of the predominant use or permanent disuse of any organ; all these are preserved by reproduction to the new individuals which arise, provided that the acquired modifications are common to both sexes, or at least to the individuals which produce the young.

In essence, a change in the environment brings about change in "needs" (besoins), resulting in change in behavior, bringing change in organ usage and development, bringing change in form over time — and thus the gradual transmutation of the species. While such a theory might explain the observed diversity of species and the first law is generally true, the main argument against Lamarckism is that experiments simply do not support the second law — purely "acquired traits" do not appear in any meaningful sense to be inherited. For example, a human child must learn how to catch a ball even though his or her parents learned the same feat when they were children.

(Though it is important to note that just because the skill of catching a ball can not be passed on from parent to child does not mean that we can rule out all other traits from being passed on in a Lamarckian fashion).

The argument that instinct in animals is evidence for hereditary knowledge is generally regarded within science as false. Such behaviours are more probably passed on through a mechanism called the Baldwin effect. Lamarck’s theories gained initial acceptance because the mechanisms of inheritance were not elucidated until later in the 19th Century, after Lamarck's death.

Several historians have argued that Lamarck's name is linked somewhat unfairly to the theory that has come to bear his name, and that Lamarck deserves credit for being an influential early proponent of the concept of biological evolution, far more than for the mechanism of evolution, in which he simply followed the accepted wisdom of his time. Lamarck died 30 years before the first publication of Charles Darwin's Origin of Species. As science historian Stephen Jay Gould has noted, if Lamarck had been aware of Darwin's proposed mechanism of natural selection, there is no reason to assume he would not have accepted it as a more likely alternative to his "own" mechanism. Note also that Darwin, like Lamarck, lacked a plausible alternative mechanism of inheritance - the particulate nature of inheritance was only to be observed by Gregor Mendel somewhat later, published in 1866. Its importance, although Darwin cited Mendel's paper, was not recognised until the Modern evolutionary synthesis in the early 1900s. An important point in its favour at the time was that Lamarck's theory contained a mechanism describing how variation is maintained, which Darwin’s own theory lacked.

[编辑] Proponents

In the 1920s, Harvard University researcher William McDougall studied the abilities of rats to correctly solve mazes. He found that children of rats that had learned the maze were able to run it faster. The first rats would get it wrong 165 times before being able to run it perfectly each time, but after a few generations it was down to 20. McDougall attributed this to some sort of Lamarckian evolutionary process.^{[來源請求]}

Ted Steele et al, formerly of the University of Wollongong, produced some indirect evidence for somatic transfer of antibody genes into sex cells via reverse transcription. Homologous DNA sequences from VDJ regions of parent mice were found in germ cells and then their offspring. However, there has been no definitive experiment. ^[1]

[编辑] Lamarckism and single-celled organisms

While Lamarckism has been discredited as an evolutionary influence for larger lifeforms, some scientists controversially argue that it can be observed among microorganisms.^[2] Whether such mutations are directed or not also remains a point of contention.

In 1988, John Cairns at the Radcliffe Infirmary in Oxford, England, and a group of other scientists renewed the Lamarckian controversy (which by then had been a dead debate for many years).^[3] The group took a mutated strain of E. coli that was unable to consume the sugar lactose and placed it in an environment where lactose was the only food source. They observed over time that mutations occurred within the colony at a rate that suggested the bacteria were overcoming their handicap by altering their own genes. Cairns, among others, dubbed the process adaptive mutagenesis.

If bacteria that had overcome their own inability to consume lactose passed on this "learned" trait to future generations, it could be argued as a form of Lamarckism; though Cairns later chose to distance himself from such a position. ^[4]. More typically, it might be viewed as a form of ontogenic evolution.

There has been some research into Lamarckism and prions. A group of researchers, for example, discovered that in yeast cells containing a specific prion protein Sup35, the yeast were able to gain new genetic material, some of which gave them new abilities such as resistance to a particular herbicide. When the researchers mated the yeast cells with cells not containing the prion, the trait reappeared in some of the resulting offspring, indicating that some information indeed was passed down, though whether or not the information is genetic is debatable: trace prion amounts in the cells may be passed to their offspring, giving the appearance of a new genetic trait where there is none.^[5]

Finally, there is growing evidence that cells can activate low-fidelity DNA polymerases in times of stress to induce mutations. While this does not directly confer advantage to the organism on the organismal level, it makes sense at the gene-evolution level. While the acquisition of new genetic traits is random, and selection remains Darwinian, the active process of identifying the necessity to mutate is considered to be Lamarckian.

[编辑] Lamarckism and societal change

Jean Molino (2000) has proposed that Lamarckian evolution may be accurately applied to cultural evolution. This was also previously suggested by Peter Medawar (1959) and Conrad Waddington (1961).