Acquired characteristics

Jean-Baptiste Lamarck

The inheritance of acquired characteristics (or characters) is the hereditary mechanism by which changes in physiology acquired over the life of an organism (such as muscle enlarged through use) are purportedly transmitted to offspring. It is also commonly referred to as the theory of adaptation equated with the evolutionary theory of French naturalist Jean-Baptiste Lamarck known as Lamarckism. Proposed in ancient times by Hippocrates and Aristotle, near to Lamarck's time the idea was commonly accepted. Comte de Buffon, before Lamarck, proposed ideas about evolution involving the concept, and even Charles Darwin, after Lamarck, developed his own theory of inheritance of acquired characters, pangenesis. The basic concept of inheritance of acquired characters was not widely rejected until the early 20th century.

Long after the triumph of the central dogma of molecular biology, which is often equated with the idea that the DNA of a cell alone determines its fate, it was the fact that the cell plasm of an egg cell, whose composition can influence the early stages of a developing embryo, is in part derived from the diploid cells of the parent, which will have a different genotype, that inspired researchers to look for examples where this is important. It is important because now the offspring will have the same traits. In a separate development, it was realized in quantitative genetics that models that included a maternal effect made more accurate predictions. Some maternal effects are acquired traits; namely, when the relevant parent's trait and offspring's trait are the same.

The original idea of inheritance of acquired characters has survived as a proverb, "use it or lose it." This phrase does not usually refer to the inheritance of traits, however; instead, it is applied to the maintenance of attributes in an individual.

Lamarckism

Lamarckism or Lamarckian evolution is a theory put forward by Lamarck based on the 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.

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. While enormously popular during the early 19th 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 Lamarckian theory of evolution in biology.

Lamarck's theory

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

Between 1794 and 1796 Erasmus 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:

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

With this in mind, Lamarck developed two laws:

1. 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.
2. 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 Mendelian inheritance were not elucidated until later in the 19th Century, after Lamarck's death.

Proponents

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.

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.

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.

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 and famine.

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. However, there has been no definitive experiment

Neo-Lamarckism is a theory of inheritance based on a modification and extension of Lamarckism, essentially maintaining the principle that genetic changes can be influenced and directed by environmental factors.

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.

In the USSR during the rule of Joseph Stalin in the 1930s the theory of inheritance of acquired characteristics was central to the dogma put forth by Trofim Lysenko, president of the Soviet Academy of Agricultural Sciences. While Lysenkoism was advanced primarily in the service of Soviet agriculture (invariably resulting in dismal failure, however), its implications for the field of human biology were not lost on the Soviet leadership. Although Lysenko and Lysenkoism came to be discredited in the USSR by the mid-1960s, the concept still finds favor in Marxist circles.

Genetic disproof

There are many formulations of the genetic disproof, but all have roughly the same structure as the following:

1. Acquired traits do not affect an organism's genome.
2. Only the genome is passed to the offspring.
3. Therefore, acquired traits cannot be passed to the offspring.

While this proof may be logically valid, it suffers from the material fallacy of begging the question, since no one who believes in inheritance of acquired characters would believe both assumptions.

References

ISBN links support NWE through referral fees

• Cairns, J. 1998. Mutation and cancer: the antecedents to our studies of adaptive mutation. Genetics 149: 1433-1440.
• Cohen, P. 2004. Lamarckism finds new lease of life in a prion. New Scientist August 21, 2004, issue 2461.
• Culotta, E. 1994. A boost for 'adaptive' mutation. Science 265: 318.
• Molino, J. 2000. Toward an evolutionary theory of music and language. In S. Brown, N. L. Wallin, and B. Merker. 2000. The Origins of Music. Cambridge, Mass: MIT. ISBN 0262232065.
• Steele, E. J., R. A. Lindley, and R. V. Blanden. 1998. Lamarck's Signature: How Retrogenes Are Changing Darwin's Natural Selection Paradigm. Perseus Books. ISBN 073820014X.
• Vetsigian K, C. Woese, and N. Goldenfeld. 2006. Collective evolution and the genetic code. PNAS 103: 10696-10701.
• Waddington, C. 1961. The human evolutionary system. In M. Banton, ed., Darwinism and the Study of Society. London: Tavistock.

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