Inheritance of acquired characters

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Jean-Baptiste Lamarck

The inheritance of acquired characters (or characteristics) 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. 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 realised 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 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.

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 (d. 1954), 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.

[edit] Genetic disproof

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

Acquired traits do not affect an organism's genome.
Only the genome is passed to the offspring.
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. This proof also suffers from logical redundancy. Although its valued by some that thoughts be explained in a uniform fashion (such as the above-used proof/disproof model), it is an insult to the intelligence of most readers to put in complex, mathematical terms what was already entirely and simplistically obvious.