Lamarckism

Textbook Lamarckism

The identification of Lamarckism with the inheritance of acquired characteristics is regarded by evolutionary biologists including Ghiselin and Gould as a falsified artifact of the subsequent history of evolutionary thought, repeated in textbooks without analysis, and wrongly contrasted with a falsified picture of Darwin's thinking. Ghiselin notes that "Darwin accepted the inheritance of acquired characteristics, just as Lamarck did, and Darwin even thought that there was some experimental evidence to support it." Gould wrote that in the late 19th 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." He argued that "the restriction of 'Lamarckism' to this relatively small and non-distinctive corner of Lamarck's thought must be labelled as more than a misnomer, and truly a discredit to the memory of a man and his much more comprehensive system."

Neo-Lamarckism

Context

The period of the history of evolutionary thought between Darwin's death in the 1880s, and the foundation of population genetics in the 1920s and the beginnings of the modern evolutionary synthesis in the 1930s, is called the eclipse of Darwinism by some historians of science. During that time many scientists and philosophers accepted the reality of evolution but doubted whether natural selection was the main evolutionary mechanism.

Among the most popular alternatives were theories involving the inheritance of characteristics acquired during an organism's lifetime. Scientists who felt that such Lamarckian mechanisms were the key to evolution were called neo-Lamarckians. They included the British botanist George Henslow (1835–1925), who studied the effects of environmental stress on the growth of plants, in the belief that such environmentally-induced variation might explain much of plant evolution, and the American entomologist Alpheus Spring Packard Jr., who studied blind animals living in caves and wrote a book in 1901 about Lamarck and his work. Also included were paleontologists like Edward Drinker Cope and Alpheus Hyatt, who observed that the fossil record showed orderly, almost linear, patterns of development that they felt were better explained by Lamarckian mechanisms than by natural selection. Some people, including Cope and the Darwin critic Samuel Butler, felt that inheritance of acquired characteristics would let organisms shape their own evolution, since organisms that acquired new habits would change the use patterns of their organs, which would kick-start Lamarckian evolution. They considered this philosophically superior to Darwin's mechanism of random variation acted on by selective pressures. Lamarckism also appealed to those, like the philosopher Herbert Spencer and the German anatomist Ernst Haeckel, who saw evolution as an inherently progressive process. The German zoologist Theodor Eimer combined Larmarckism with ideas about orthogenesis, the idea that evolution is directed towards a goal.

With the development of the modern synthesis of the theory of evolution, and a lack of evidence for a mechanism for acquiring and passing on new characteristics, or even their heritability, Lamarckism largely fell from favour. Unlike neo-Darwinism, neo-Lamarckism is a loose grouping of largely heterodox theories and mechanisms that emerged after Lamarck's time, rather than a coherent body of theoretical work.

19th century

Neo-Lamarckian versions of evolution were widespread in the late 19th century. The idea that living things could to some degree choose the characteristics that would be inherited allowed them to be in charge of their own destiny as opposed to the Darwinian view, which placed them at the mercy of the environment. Such ideas were more popular than natural selection in the late 19th century as it made it possible for biological evolution to fit into a framework of a divine or naturally willed plan, thus the neo-Lamarckian view of evolution was often advocated by proponents of orthogenesis. According to the historian of science Peter J. Bowler, writing in 2003:

One of the most emotionally compelling arguments used by the neo-Lamarckians of the late nineteenth century was the claim that Darwinism was a mechanistic theory which reduced living things to puppets driven by heredity. The selection theory made life into a game of Russian roulette, where life or death was predetermined by the genes one inherited. The individual could do nothing to mitigate bad heredity. Lamarckism, in contrast, allowed the individual to choose a new habit when faced with an environmental challenge and shape the whole future course of evolution.

Scientists from the 1860s onwards conducted numerous experiments that purported to show Lamarckian inheritance. Some examples are described in the table.

Early 20th century

A century after Lamarck, scientists and philosophers continued to seek mechanisms and evidence for the inheritance of acquired characteristics. Experiments were sometimes reported as successful, but from the beginning these were either criticised on scientific grounds or shown to be fakes. For instance, in 1906, the philosopher Eugenio Rignano argued for a version that he called "centro-epigenesis", but it was rejected by most scientists. Some of the experimental approaches are described in the table.

Late 20th century

The British anthropologist Frederic Wood Jones and the South African paleontologist Robert Broom supported a neo-Lamarckian view of human evolution. The German anthropologist Hermann Klaatsch relied on a neo-Lamarckian model of evolution to try and explain the origin of bipedalism. Neo-Lamarckism remained influential in biology until the 1940s when the role of natural selection was reasserted in evolution as part of the modern evolutionary synthesis. Herbert Graham Cannon, a British zoologist, defended Lamarckism in his 1959 book Lamarck and Modern Genetics. In the 1960s, "biochemical Lamarckism" was advocated by the embryologist Paul Wintrebert.

Neo-Lamarckism was dominant in French biology for more than a century. French scientists who supported neo-Lamarckism included Edmond Perrier (1844–1921), Alfred Giard (1846–1908), Gaston Bonnier (1853–1922) and Pierre-Paul Grassé (1895–1985). They followed two traditions, one mechanistic, one vitalistic after Henri Bergson's philosophy of evolution.

In 1987, Ryuichi Matsuda coined the term "pan-environmentalism" for his evolutionary theory which he saw as a fusion of Darwinism with neo-Lamarckism. He held that heterochrony is a main mechanism for evolutionary change and that novelty in evolution can be generated by genetic assimilation. His views were criticized by Arthur M. Shapiro for providing no solid evidence for his theory. Shapiro noted that "Matsuda himself accepts too much at face value and is prone to wish-fulfilling interpretation."

Ideological neo-Lamarckism

A form of Lamarckism was revived in the Soviet Union of the 1930s when Trofim Lysenko promoted the ideologically driven research programme, Lysenkoism; this suited the ideological opposition of Joseph Stalin to genetics. Lysenkoism influenced Soviet agricultural policy which in turn was later blamed for the numerous massive crop failures experienced within Soviet states.

Critique

George Gaylord Simpson in his book Tempo and Mode in Evolution (1944) claimed that experiments in heredity have failed to corroborate any Lamarckian process. Simpson noted that neo-Lamarckism "stresses a factor that Lamarck rejected: inheritance of direct effects of the environment" and neo-Lamarckism is closer to Darwin's pangenesis than Lamarck's views. Simpson wrote, "the inheritance of acquired characters, failed to meet the tests of observation and has been almost universally discarded by biologists."

Zirkle pointed out that Lamarck did not originate the hypothesis that acquired characteristics could be inherited, so it is incorrect to refer to it as Lamarckism:

What Lamarck really did was to accept the hypothesis that acquired characters were heritable, a notion which had been held almost universally for well over two thousand years and which his contemporaries accepted as a matter of course, and to assume that the results of such inheritance were cumulative from generation to generation, thus producing, in time, new species. His individual contribution to biological theory consisted in his application to the problem of the origin of species of the view that acquired characters were inherited and in showing that evolution could be inferred logically from the accepted biological hypotheses. He would doubtless have been greatly astonished to learn that a belief in the inheritance of acquired characters is now labeled "Lamarckian," although he would almost certainly have felt flattered if evolution itself had been so designated.

Peter Medawar wrote regarding Lamarckism, "very few professional biologists believe that anything of the kind occurs—or can occur—but the notion persists for a variety of nonscientific reasons." Medawar stated there is no known mechanism by which an adaptation acquired in an individual's lifetime can be imprinted on the genome and Lamarckian inheritance is not valid unless it excludes the possibility of natural selection, but this has not been demonstrated in any experiment.

Martin Gardner wrote in his book Fads and Fallacies in the Name of Science (1957):

A host of experiments have been designed to test Lamarckianism. All that have been verified have proved negative. On the other hand, tens of thousands of experiments— reported in the journals and carefully checked and rechecked by geneticists throughout the world— have established the correctness of the gene-mutation theory beyond all reasonable doubt... In spite of the rapidly increasing evidence for natural selection, Lamarck has never ceased to have loyal followers.... There is indeed a strong emotional appeal in the thought that every little effort an animal puts forth is somehow transmitted to his progeny.

According to Ernst Mayr, any Lamarckian theory involving the inheritance of acquired characters has been refuted as "DNA does not directly participate in the making of the phenotype and that the phenotype, in turn, does not control the composition of the DNA." Peter J. Bowler has written that although many early scientists took Lamarckism seriously, it was discredited by genetics in the early twentieth century.

Mechanisms resembling Lamarckism

Studies in the field of epigenetics, genetics, somatic hypermutation, and the morphic resonance theory of Rupert Sheldrake have highlighted the possible inheritance of traits acquired by the previous generation. However, the characterization of these findings as Lamarckism has been disputed.

Transgenerational epigenetic inheritance

Epigenetic inheritance has been argued by scientists including Eva Jablonka and Marion J. Lamb to be Lamarckian. Epigenetics is based on hereditary elements other than genes that pass into the germ cells. These include methylation patterns in DNA and chromatin marks on histone proteins, both involved in gene regulation. These marks are responsive to environmental stimuli, differentially affect gene expression, and are adaptive, with phenotypic effects that persist for some generations. The mechanism may also enable the inheritance of behavioral traits, for example in chickens, rats and human populations that have experienced starvation, DNA methylation resulting in altered gene function in both the starved population and their offspring. Methylation similarly mediates epigenetic inheritance in plants such as rice. Small RNA molecules, too, may mediate inherited resistance to infection. Handel and Ramagopalan commented that "epigenetics allows the peaceful co-existence of Darwinian and Lamarckian evolution."

Joseph Springer and Dennis Holley commented in 2013 that:

Lamarck and his ideas were ridiculed and discredited. In a strange twist of fate, Lamarck may have the last laugh. Epigenetics, an emerging field of genetics, has shown that Lamarck may have been at least partially correct all along. It seems that reversible and heritable changes can occur without a change in DNA sequence (genotype) and that such changes may be induced spontaneously or in response to environmental factors—Lamarck's "acquired traits." Determining which observed phenotypes are genetically inherited and which are environmentally induced remains an important and ongoing part of the study of genetics, developmental biology, and medicine.

The prokaryotic CRISPR system and Piwi-interacting RNA could be classified as Lamarckian, within a Darwinian framework. However, the significance of epigenetics in evolution is uncertain. Critics such as the evolutionary biologist Jerry Coyne point out that epigenetic inheritance lasts for only a few generations, so it is not a stable basis for evolutionary change.

The evolutionary biologist T. Ryan Gregory contends that epigenetic inheritance should not be considered Lamarckian. According to Gregory, Lamarck did not claim that the environment directly affected living things. Instead, Lamarck "argued that the environment created needs to which organisms responded by using some features more and others less, that this resulted in those features being accentuated or attenuated, and that this difference was then inherited by offspring." Gregory has stated that Lamarckian evolution in epigenetics is more like Darwin's point of view than Lamarck's.

In 2007, David Haig wrote that research into epigenetic processes does allow a Lamarckian element in evolution but the processes do not challenge the main tenets of the modern evolutionary synthesis as modern Lamarckians have claimed. Haig argued for the primacy of DNA and evolution of epigenetic switches by natural selection. Haig has written that there is a "visceral attraction" to Lamarckian evolution from the public and some scientists, as it posits the world with a meaning, in which organisms can shape their own evolutionary destiny.

Thomas Dickens and Qazi Rahman (2012) have argued that epigenetic mechanisms such as DNA methylation and histone modification are genetically inherited under the control of natural selection and do not challenge the modern synthesis. They dispute the claims of Jablonka and Lamb on Lamarckian epigenetic processes.

In 2015, Khursheed Iqbal and colleagues discovered that although "endocrine disruptors exert direct epigenetic effects in the exposed fetal germ cells, these are corrected by reprogramming events in the next generation." Also in 2015, Adam Weiss argued that bringing back Lamarck in the context of epigenetics is misleading, commenting, "We should remember [Lamarck] for the good he contributed to science, not for things that resemble his theory only superficially. Indeed, thinking of CRISPR and other phenomena as Lamarckian only obscures the simple and elegant way evolution really works."

Somatic hypermutation and reverse transcription to germline

In the 1970s, the Australian immunologist Edward J. Steele developed a neo-Lamarckian theory of somatic hypermutation within the immune system and coupled it to the reverse transcription of RNA derived from body cells to the DNA of germline cells. This reverse transcription process supposedly enabled characteristics or bodily changes acquired during a lifetime to be written back into the DNA and passed on to subsequent generations.

The mechanism was meant to 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 generated via somatic hypermutation in B-cells. The messenger RNA products of these somatically novel genes were captured by retroviruses endogenous to the B-cells and were then transported through the bloodstream where they could breach the Weismann or soma-germ barrier and reverse transcribe the newly acquired genes into the cells of the germ line, in the manner of Darwin's pangenes.

The historian of biology Peter J. Bowler noted in 1989 that other scientists had been unable to reproduce his results, and described the scientific consensus at the time:

There is no feedback of information from the proteins to the DNA, and hence no route by which characteristics acquired in the body can be passed on through the genes. The work of Ted Steele (1979) provoked a flurry of interest in the possibility that there might, after all, be ways in which this reverse flow of information could take place. ... [His] mechanism did not, in fact, violate the principles of molecular biology, but most biologists were suspicious of Steele's claims, and attempts to reproduce his results have failed.

Bowler commented that "[Steele's] work was bitterly criticized at the time by biologists who doubted his experimental results and rejected his hypothetical mechanism as implausible."

Hologenome theory of evolution

The hologenome theory of evolution, while Darwinian, has Lamarckian aspects. An individual animal or plant lives in symbiosis with many microorganisms, and together they have a "hologenome" consisting of all their genomes. The hologenome can vary like any other genome by mutation, sexual recombination, and chromosome rearrangement, but in addition it can vary when populations of microorganisms increase or decrease (resembling Lamarckian use and disuse), and when it gains new kinds of microorganism (resembling Lamarckian inheritance of acquired characteristics). These changes are then passed on to offspring. The mechanism is largely uncontroversial, and natural selection does sometimes occur at whole system (hologenome) level, but it is not clear that this is always the case.

Baldwin effect

The Baldwin effect, named after the psychologist James Mark Baldwin by George Gaylord Simpson in 1953, proposes that the ability to learn new behaviours can improve an animal's reproductive success, and hence the course of natural selection on its genetic makeup. Simpson stated that the mechanism was "not inconsistent with the modern synthesis" of evolutionary theory, though he doubted that it occurred very often or could be proven to occur. He noted that the Baldwin effect provided a reconciliation between the neo-Darwinian and neo-Lamarckian approaches, something that the modern synthesis had seemed to render unnecessary. In particular, the effect allows animals to adapt to a new stress in the environment through behavioural changes, followed by genetic change. This somewhat resembles Lamarckism but without requiring animals to inherit characteristics acquired by their parents. The Baldwin effect is broadly accepted by Darwinists.

In sociocultural evolution

Within the field of cultural evolution, Lamarckism has been applied as a mechanism for dual inheritance theory. Gould viewed culture as a Lamarckian process whereby older generations transmitted adaptive information to offspring via the concept of learning. In the history of technology, components of Lamarckism have been used to link cultural development to human evolution by considering technology as extensions of human anatomy.