Lamarckism - Neo-Lamarckism

Neo-Lamarckism

Unlike neo-Darwinism, the term neo-Lamarckism refers more to a loose grouping of largely heterodox 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 found that offspring 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. Oscar Werner Tiegs and Wilfred Eade Agar later showed McDougall's results to be incorrect, caused by poor experimental controls.

At around the same time, Ivan Pavlov, who was also a Lamarckist, claimed to have observed a similar phenomenon in animals being subject to conditioned reflex experiments. He claimed that with each generation, the animals became easier to condition. However, Pavlov never suggested a mechanism to explain these observations.

Peter Bowler wrote that Edward Drinker Cope was a neo-Lamarckian as he believed it allowed living things to be in charge of their own destiny as opposed to the Darwinian view of living things being a puppet at the mercy of the environment. Cope's neo-Lamarckism had claimed that the organism could respond to any challenge by choosing to adapt to a new way of life. The neo-Lamarckian version of evolution was more popular than Darwin's in the late 19th century as it made it possible for biological evolution to fit into a framework of a divine or natural directed plan, thus the neo-Lamarckian view of evolution was often advocated by proponents of orthogenesis.

In the early 20th century Frederic Wood Jones and Robert Broom had supported a neo-Lamarckian view of human evolution as opposed to the Darwinian view. Neo-Lamarckism often argued for parallel evolution and independent evolution of species. Hermann Klaatsch had relied on a neo-Lamarckian model of evolution to try and explain the origin of bipedalism. Klaatsch's model had claimed that human races had evolved independent of each other and because of this his model had influenced the belief of polygenism. 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.

Later supporters of Neo-Lamarckism were George Bernard Shaw and Arthur Koestler who both claimed Lamarckism is more humane, and optimistic than Darwinism.

Soma to germ-line feedback

In the 1970s the immunologist Ted Steele, formerly of the University of Wollongong, and colleagues, proposed a neo-Lamarckian mechanism to try 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 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.

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 affect 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 many experiments have validated it), its significance to the evolutionary process is 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.