Acquired characteristics
Inheritance of acquired characteristics, or inheritance of acquired characters is the once widely accepted idea that physiological modifications acquired by an organism can be inherited by the offspring. Acquired characteristics (or characters) are those changes in the structure or function of an organism that are the result of use, disuse, environmental influences, disease, mutilation, and so forth, such as a muscle that is enlarged through use or mice that have their tails cut off. The theory of the inheritance of acquired characteristics, or "soft inheritance," holds that an organism experiencing such a modification can transmit such a character to its offspring.
This theory is commonly equated with the evolutionary theory of French naturalist Jean-Baptiste Lamarck known as Lamarckism. While Lamarck is sometimes viewed as the founder of the concept, in reality this theory was proposed in ancient times by Hippocrates and Aristotle, and Comte de Buffon, before Lamarck, proposed ideas about evolution involving the concept. Even Charles Darwin, after Lamarck, discussed positively this view in his seminal work, Origin of Species.
While the theory of the inheritance of acquired characteristics was enormously popular during the early nineteenth century as an explanation for the complexity observed in living systems, 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 theory of inheritance of acquired characteristics in biology, although there are proponents for its working on the microbial level or in epigenetic inheritance.
However, in a wider context, the theory of inheritance of acquired characteristics does remain a useful concept when examining the evolution of cultures and ideas and is generally held in terms of some religious views, such as karma and inheritance of sin. In the case of religion, many traditions accept the view that there is an inheritance of acquired spiritual traits—that actions taken in one's life can be passed down in the form of spiritual merit or demerit to one's lineage (Wilson 1991).
Lamarckism and the inheritance of acquired characteristics
Lamarckism or Lamarckian evolution is a theory put forward by Lamarck based on the heritability of acquired characteristics. Lamarck proposed that individual efforts during the lifetime of the organisms were the main mechanism driving species to adaptation, as they supposedly would acquire adaptive changes and pass them on to offspring.
The identification of "Lamarckism" with the inheritance of acquired characteristics is regarded by some as an artifact of the subsequent history of evolutionary thought, repeated in textbooks without analysis. Stephen Jay Gould wrote that late nineteenth century evolutionists "re-read Lamarck, cast aside the guts of it … and elevated one aspect of the mechanics—inheritance of acquired characters—to a central focus it never had for Lamarck himself" (Gould 1980). He argued that "the restriction of "Lamarckism" to this relatively small and non-distinctive corner of Lamarck's thought must be labeled as more than a misnomer, and truly a discredit to the memory of a man and his much more comprehensive system" (Gould 2002). Gould advocated defining "Lamarckism" more broadly, in line with Lamarck's overall evolutionary theory.
Lamarck's theory
Between 1794 and 1796 Erasmus Darwin, grandfather of Charles Darwin, wrote Zoönomia suggesting "that all warm-blooded animals have arisen from one living filament," and "with the power of acquiring new parts" in response to stimuli, with each round of "improvements" being inherited by successive generations.
Subsequently Lamarck proposed in his Philosophie Zoologique of 1809 the theory that characteristics that were "needed" were acquired (or diminished) during the lifetime of an organism were 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 based his theory on two observations, in his day considered to be generally true:
- Individuals lose characteristics they do not require (or use) and develop characteristics that are useful.
- Individuals inherit the traits of their ancestors.
With this in mind, Lamarck developed two laws:
- Law of use and disuse. "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."
- Inheritance of acquired traits. "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."
Examples of Lamarckism would include:
- Giraffes stretching their necks to reach leaves high in trees 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.
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.
The argument that instinct in animals is evidence for hereditary knowledge is generally regarded within science as false. Such behaviors 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 nineteenth 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 recognized until the modern evolutionary synthesis in the early 1900s. An important point in its favor at the time was that Lamarck's theory contained a mechanism describing how variation is maintained, which Darwin’s own theory lacked.
Proponents
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 modeled 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 (Desmond and Moore 1991). Darwin called his Lamarckian hypothesis Pangenesis, and explained it in the final chapter of his book Variation in Plants and Animals under Domestication, after describing numerous examples to demonstrate what he considered to be the inheritance of acquired characteristics. Pangenesis, which he emphasised was a hypothesis, was based on the idea that somatic cells would, in response to environmental stimulation (use and disuse), throw off 'gemmules' which traveled around the body (though not in necessarily in the bloodstream). These pangenes were microscopic particles that supposedly contained information about the characteristics of their parent cell, and Darwin believed that they eventually accumulated in the germ cells where they could pass on to the next generation the newly acquired characteristics of the parents.
Darwin's half-cousin, Francis Galton carried out experiments on rabbits, with Darwin's cooperation, in which he transfused the blood of one variety of rabbit into another variety in the expectation that its offspring would show some characteristics of the first. They did not, and Galton declared that he had disproved Darwin's hypothesis of Pangenesis, but Darwin objected, in a letter to ''Nature'' that he had done nothing of the sort, since he had never mentioned blood in his writings. He pointed out that he regarded pangenesis as occurring in Protozoa and plants, which have no blood (Darwin 1871). With the development of the modern synthesis of the theory of evolution and a lack of evidence for either a mechanism or even the heritability acquired characteristics, Lamarckism largely fell from favor.
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 sympathizer 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 ideologically driven research influenced Soviet agricultural policy which in turn 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.
Steele et al. (1998) 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.
Neo-Lamarckism
Unlike neo-Darwinism, the term neo-Lamarckism refers more to a loose grouping of largely heterodoxical theories and mechanisms that emerged after Lamarck's time, than to any coherent body of theoretical work.
In the 1920s, Harvard University researcher William McDougall studied the abilities of rats to correctly solve mazes. He claimed that offspring of rats that had learned the maze were able to run it faster. The first rats would get it wrong an average of 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.
At around the same time, Russian physiologist Ivan Pavlov, who was also a Lamarckist, claimed to have observed a similar phenomena in animals being subject to conditioned reflex experiments. He claimed that with each generation, the animals became easier to condition.
Neither McDougall nor Pavlov suggested a mechanism to explain their observations.
Soma to germ line feedback
In the 1970s, the immunologist Ted Steele, formerly of the University of Wollongong, and colleagues, proposed a neo-Lamarckiam mechanism to try and explain why homologous DNA sequences from the VDJ gene regions of parent mice were found in their germ cells and seemed to persist in the offspring for a few generations. The mechanism involved the somatic selection and clonal amplification of newly acquired antibody gene sequences that were generated via somatic hyper-mutation in B-cells. The mRNA products of these somatically novel genes were captured by retroviruses endogenous to the B-cells and were then transported through the blood stream where they could breach the soma-germ barrier and retrofect (reverse transcribe) the newly acquired genes into the cells of the germ line. Although Steele was advocating this theory for the better part of two decades, little more than indirect evidence was ever acquired to support it. An interesting attribute of this idea is that it strongly resembles Darwin's own theory of pangenesis, except in the soma to germ line feedback theory, pangenes are replaced with realistic retroviruses (Steele et al. 1998).
Epigenetic inheritance
Forms of 'soft' or epigenetic inheritance within organisms have been suggested as neo-Lamarckian in nature by such scientists as Eva Jablonka and Marion J. Lamb. In addition to "hard" or genetic inheritance, involving the duplication of genetic material and its segregation during meiosis, there are other hereditary elements that pass into the germ cells also. These include things like methylation patterns in DNA and chromatin marks, both of which regulate the activity of genes. These are considered "Lamarckian" in the sense that they are responsive to environmental stimuli and can differentially effect gene expression adaptively, with phenotypic results that can persist for many generations in certain organisms. Although the reality of epigenetic inheritance is not doubted (as countless experiments have validated it) its significance to the evolutionary process is however uncertain. Most neo-Darwinians consider epigenetic inheritance mechanisms to be little more than a specialized form of phenotypic plasticity, with no potential to introduce evolutionary novelty into a species lineage (Jablonka and Lamb 1995).
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. 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) (Mulligan 2002; Foster 2000). 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 (Cairns 2004). 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 (Cohen 2004).
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.
Inheritance of acquired characteristics and societal change
Jean Molino (2000) has proposed that Lamarckian evolution or soft inheritance may be accurately applied to cultural evolution. This was also previously suggested by Peter Medawar (1959) and Conrad Waddington (1961). K. N. Laland and colleagues have recently suggested that human culture can be looked upon as an ecological niche like phenomena, where the effects of cultural niche construction are transmissible from one generation to the next. One interpretation of the Meme theory is that memes are both Darwinian and Lamarckian in nature, as in addition to being subject to selection pressures based on their ability to differentially influence human minds, memes can be modified and the effects of that modification passed on.
ReferencesISBN links support NWE through referral fees
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