Inheritance of acquired characteristics
The inheritance of acquired characteristics is a hypothesis that physiological changes acquired over the life of an organism (such as the enlargement of a muscle through repeated use) may be transmitted to offspring. The hypothesis is often called Lamarckism, as it has misleadingly been equated with the evolutionary theory of the French naturalist Jean-Baptiste Lamarck (1744-1829). The idea was however already known to Hippocrates and Aristotle in ancient times, and was widely accepted by the eighteenth century. Lamarck has been used in biology schoolbooks as a mistaken forerunner of Charles Darwin, ignoring the fact that Darwin's theory of pangenesis was Lamarckian, implying the inheritance of acquired characteristics.
The inheritance of acquired characteristics was proposed in ancient times by Hippocrates and Aristotle, and was commonly accepted near to Lamarck's time; Erasmus Darwin had described it in his Zoonomia, 1794. The historian of science Conway Zirkle wrote that:
Lamarck was neither the first nor the most distinguished biologist to believe in the inheritance of acquired characters. He merely endorsed a belief which had been generally accepted for at least 2,200 years before his time and used it to explain how evolution could have taken place. The inheritance of acquired characters had been accepted previously by Hippocrates, Aristotle, Galen, Roger Bacon, Jerome Cardan, Levinus Lemnius, John Ray, Michael Adanson, Jo. Fried. Blumenbach and Erasmus Darwin among others.
Lamarck published his theory in 1809. He noticed that fossils in a sequence had grown closer to living species with time. While most of his book covered other theories including orthogenesis, in a section on heredity (not evolution) he mentioned the theory of use and disuse, namely that body parts used more often become stronger and larger, while parts not used slowly waste away, and the inheritance of acquired characteristics. This, and the example of the giraffe straining its neck to reach high leaves and thus becoming longer, has been used as a counterfoil to Darwinian evolution by natural selection in biology textbooks such as Campbell and Reece. The evolutionary biologist Michael Ghiselin has called this a falsified artifact of the subsequent history of evolutionary thought, repeated in textbooks without analysis.
Charles Darwin, after Lamarck, developed his own blending theory of inheritance of acquired characters, pangenesis. He suggested that small particles, gemmules, migrated from every part of the body to the reproductive organs, where they contributed to the gametes. Characteristics from an organ enlarged or reduced by use or disuse could thus be inherited.
The basic concept of inheritance of acquired characteristics was widely rejected in the early 20th century. However, in the 1920s, the Harvard University researcher William McDougall studied the abilities of rats to choose the correct exit from a water-filled tank. His reports claimed that offspring of rats that had been trained to choose a particular exit made fewer errors while learning the task. In his data, the first rats would get it wrong 165 times before being able to choose the correct exit each time, but after a few generations, it was down to 20. McDougall attributed this to some sort of Lamarckian evolutionary process. However his experiments were criticised for having several methodological problems and poor record-keeping. McDougall's findings were replicated by Agar et al. (1954), but they found that there was a partial reversal of the effect in subsequent generations and, more importantly, that similar improvement was seen in a control group of rats whose ancestors had not been trained. They concluded that the effect was not evidence of the inheritance of acquired characteristics.
During the rule of Joseph Stalin in the USSR in the 1930s, the theory of inheritance of acquired characteristics was one of the proposals put forth by Trofim Lysenko, president of the Soviet Academy of Agricultural Sciences. Lysenkoism was advanced primarily in service to Soviet agriculture. Lysenko's research contributed to widespread famines and was in the end mistaken about mendelian genetics.
The idea that germline cells contain information that passes to each generation unaffected by experience and independent of the somatic (body) cells, came to be referred to as the Weismann barrier. It became conventional wisdom that the only real form of inheritance was hard inheritance, and that any idea of soft inheritance was mistaken.
August Weismann conducted the experiment of removing the tails of 68 white mice, repeatedly over 5 generations, and reporting that no mice were born in consequence without a tail or even with a shorter tail. He stated that "901 young were produced by five generations of artificially mutilated parents, and yet there was not a single example of a rudimentary tail or of any other abnormality in this organ."
Transgenerational epigenetic inheritance
Recently, researchers have reexamined soft inheritance in light of discoveries in transgenerational epigenetics. In 2008, Heijmans and colleagues studied people born during the Dutch famine of 1944. Adults conceived during the famine had distinct epigenetic marks that their siblings born before or after the famine lacked. These marks reduced the production of insulin-like growth factor 2 (IGF2), affecting the children's growth. While transgenerational epigenetic inheritance could have occurred, the findings could also be explained by in utero modifications due to famine, rather than germline inheritance. Further, environmental stress in experimental mice that caused aggressive behavior in males caused the same behavior in their offspring, who had DNA methylation patterns changes for particular genes.
The mechanism of transgenerational epigenetic inheritance appears to involve long noncoding RNAs (lncRNAs), which are transcripts generally expressed from regions that are thought not to code for proteins. Some lncRNAs bind to transcripts from protein coding genes. Associated chromatin-remodeling proteins then modify local chromatin and DNA through mechanisms such as DNA methylation, suppressing gene expression. Kevin Morris's 2012 article in The Scientist discusses heritability of epigenetic changes in depth.
- Martin, Elizabeth; Hine, Robert. (2015). A Dictionary of Biology. Oxford University Press. p. 6. ISBN 978-0-19-871437-8
- Zirkle, Conway (1935). "The Inheritance of Acquired Characters and the Provisional Hypothesis of Pangenesis". The American Naturalist. 69: 417–445. doi:10.1086/280617.
- Gould, Stephen Jay (2001). The lying stones of Marrakech : penultimate reflections in natural history. Vintage. pp. 119–121. ISBN 978-0-09-928583-0.
- Campbell, Neil; Reece, Jane (March 2011) . "22". Biology (Sixth ed.). Benjamin Cummings. p. 431.
- Ghiselin, Michael T. (1994). "The Imaginary Lamarck: A Look at Bogus "History" in Schoolbooks". The Textbook Letter. The Textbook League (September-October 1994).
- Darwin, Charles (April 27, 1871). "Pangenesis". Nature. London: Nature Publishing Group. 3 (78): 502–503. Bibcode:1871Natur...3..502D. doi:10.1038/003502a0. Retrieved 2015-10-20.
- Agar, W.E.; Drummond, F.H.; Tiegs, O.W.; Gunson, M.M. (1954). "Fourth (final) report on a test of McDougall's Lamarckian experiment on the training of rats" (PDF). Journal of Experimental Biology. 31 (3): 307–21.
- Crew, F. A. E. (1936). "A Repetition of McDougall's Lamarckian Experiment". Journal of Genetics. 33 (1): 61–102. doi:10.1007/BF03027604.
- Crew, F.A.E. A repetition of McDougall's lamarckian experiment Journal of Genetics, 1936
- Tollefsbol, Trygve (2017). Handbook of Epigenetics: The New Molecular and Medical Genetics. Elsevier Science. p. 234. ISBN 978-0-12-805477-2. Originally published in Weismann's 1889 Essays Upon Heredity.
- Heijmans, B. T.; Tobi, E. W.; Stein, A. D.; Putter, H.; Blauw, G. J.; Susser, E. S.; Slagboom, P. E.; Lumey, L. H. (2008). "Persistent epigenetic differences associated with prenatal exposure to famine in humans". Proceedings of the National Academy of Sciences. 105 (44): 17046–9. Bibcode:2008PNAS..10517046H. doi:10.1073/pnas.0806560105. JSTOR 25465222. PMC . PMID 18955703.
- Franklin, Tamara B.; Mansuy, Isabelle M. (2010). "Epigenetic inheritance in mammals: Evidence for the impact of adverse environmental effects". Neurobiology of Disease. 39 (1): 61–5. doi:10.1016/j.nbd.2009.11.012. PMID 19931614.
- Morris, Kevin V. (October 1, 2012). "Lamarck and the Missing Lnc". The Scientist.