Genome. Darwin and Mendel today: A comment on Singh s paper

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1 Genome Darwin and Mendel today: A comment on Singh s paper Journal: Genome Manuscript ID gen r1 Manuscript Type: Comment Date Submitted by the Author: 09-Nov-2015 Complete List of Authors: Liu, Yongsheng; Henan Institute of Science and Technology; University of Alberta, Biochemistry Li, Xiuju ; Henan Institute of Science and Technology; University of Alberta Keyword: Darwin, Mendel, Genetics, Pangenesis, Mendelian inheritance

2 Page 1 of 7 Genome Comment Darwin and Mendel today: A comment on Singh s paper Yongsheng Liu and Xiuju Li Abstract: We comment on a recent paper by Rama Singh, who concludes that Mendel deserved to be called the father of genetics, and Darwin would not have understood the significance of Mendel s paper had he read it. We argue that Darwin should have been regarded as the father of genetics not only because he was the first to formulate a unifying theory of heredity, variation and development -- Pangenesis, but also because he clearly described almost all genetical phenomena of fundamental importance, including what he called prepotency and what we now call dominance or Mendelian inheritance. The word gene evolved from Darwin s imagined gemmules, instead of Mendel s so-called factors. Key words: Darwin, Mendel, Genetics, Pangenesis, Mendelian inheritance We read with great interest the article by Rama Singh (Genome, vol. 58, iss. 9). This is a well-written article that discusses several important questions pertaining to Darwin and Mendel, and includes many interesting study results. Although we share with him many views, we are afraid that some of his views are too one-sided and do not consider all the available information. It is well known that this year marks the 150 th anniversary of Mendel s presentation of his paper Experiments in plant hybridization before the Natural History Society of Brno. Less well known is that by the time Mendel s paper 1

3 Genome Page 2 of 7 appeared, Darwin had formulated his Pangenesis, a genetical theory he constructed to explain a far wider range of phenomena than Mendel had considered. He dispatched his manuscript of Pangenesis to Thomas Henry Huxley for comments on May 27, 1865 (Darwin 1888; Olby 1963). Darwin s theory of evolution is familiar to all, and the term natural selection has passed into everyday language. However, Darwin regarded his The Origin of Species as an Abstract, an incomplete explanation of his theory of evolution. It is well known that evolution is a process of variation and heredity, and variation is the fountainhead of evolution. Darwin was strongly aware of the necessity of later publishing his theory of variation and heredity. In 1868, he published his two-volume work The Variations of Animals and Plants under Domestication. It is in this work that Darwin came nearest to genetics, and presented his Pangenesis. The most distinctive feature of Pangenesis is the existence of inherited molecules called gemmules, and their production by cells. Darwin s hypothetical gemmules were minute and numerous, and were supposed to be thrown off from all cells at every stage of development. They were capable of selfreplication, diffused from cell to cell and through the body, and transmitted from parents to offspring. By his Pangenesis, Darwin provided a mechanistic explanation for a considerable variety of biological phenomena pertaining to heredity, variation and development. It is the opinion of Darwin that his theory of evolution by natural selection and his theory of heredity and variation by Pangenesis are equally important, like his two legs. During the period from the late 1860s until the rediscovery of Mendel s work in 1900, Darwin s Pangenesis was one of the most widely discussed theories and had the most influence. It greatly influenced several subsequent theories of heredity, particularly 2

4 Page 3 of 7 Genome those of Francis Galton, August Weismann and Hugo de Vries. It should be noted that the term gene evolved from pangen (pangene), a substitute for the term gemmules in Darwin s Pangenesis. Singh (2015) concludes that Mendel deserved to be called the father of genetics. We argue that Darwin should have been regarded as the father of genetics not only because he was the first to formulate a genetical theory, but also because he clearly described almost all genetical phenomena of fundamental importance, such as prepotency (dominance), sports (mutation), atavism (reversion), regeneration, heterosis (hybrid vigor), inbreeding degeneration, sex-limited inheritance, inheritance at corresponding ages, graft hybridization, xenia (the effect of foreign pollen on fruits and seeds), telegony (the effect of a previous mating on subsequent progeny), Yarrell s law (which states that in some crosses, a parent of an older breed will have more influence on the character of the offspring than a parent of a younger breed), and the inheritance of acquired characters (Lamarckian inheritance, now known as transgenerational epigenetic inheritance). There was no place for so many facts in Mendel s single paper. It is true that Mendel was the first to apply the knowledge of mathematics and statistics to a biological problem. His outstanding contribution was his experimental methodology, and his genius was in depth rather than in breadth (Dobzhansky, 1965). It was not obvious that Mendel s paper also could furnish a basis for a considerable variety of hereditary phenomena that Darwin described. It is not our intention to minimize the importance of Mendel s work in order to exalt Darwin s contributions to genetics and to rehabilitate his Pangenesis, but we must try to see things objectively. 3

5 Genome Page 4 of 7 Singh (2015) states that Darwin would not have understood the significance of Mendel s paper had he read it. We fear that we are unable to agree with him in this point. A careful reading of Darwin s book reveals that he had knowledge of the essential facts on which Mendel established his laws. In the section on Prepotency in the transmission of character of The Variation of Animals and Plants under Domestication, Darwin presented in careful detail experiments that are similar to Mendel s. He found that when the common snapdragon was crossed with the peloric variety, the former prevailed in the first generation to the exclusion of the latter. The hybrid plants which perfectly resembled the common snapdragon were self-fertilized, and yielded in the second generation 88 common and 37 peloric plants, a ratio of 2.37 : 1 approaching 3 : 1 (3). By his Pangenesis, Darwin attempted to explain major classes of facts and observations, including what he called prepotency and what we now call dominance or Mendelian inheritance. As Darwin (1868) wrote: when two forms are crossed, one is not rarely found to be prepotent in the transmission of character over the other; and this we can explain only by again assuming that the one form has some advantage in the number, vigour or affinity of its gemmules. He proposed that the sexual elements of a hybrid consisted of two kinds of gemmules or character-carriers: pure gemmules and combined or hybridized gemmules. When two hybrids pair, the combination of pure gemmules derived from the one hybrid with the pure gemmules of the same parts derived from the other would necessarily lead to complete reversion of character (Darwin 1868). He explained further that pure gemmules in combination with hybridized gemmules would lead to partial reversion and hybridized gemmules derived from both parent hybrids would simply reproduce the original hybrid form. Obviously, Darwin s theoretical statement is 4

6 Page 5 of 7 Genome virtually a statement of the conditions of things in homozygosis and heterozygosis, in principle as we have it today (Roberts 1919). For 150 years, Darwin s Pangenesis has been neither understood nor accepted, and only now are we beginning to rethink about it. Today, it is widely recognized that cells can actively release into the extracellular environment diverse types of molecules, such as circulating DNA, mobile RNAs and prions, which agree beautifully with Darwin s imagined gemmules (Liu 2008). There is also striking evidence for telegony (Liu 2011; Crean et al. 2014), graft hybridization (Liu 2006; Fuentes et al. 2014) and the inheritance of acquired characters (Liu 2007; Rechavi et al. 2014), which Darwin s Pangenesis supposedly explains. We believe that Darwin s Pangenesis, if and when sustained or rediscovered, would have a tremendous impact on the development of genetics and evolution (Liu and Li 2014). Received 6 November Accepted 10 November 2015 Y-S. Liu. and X-J. Li. Henan Collaborative Innovation Center of Modern Biological Breeding, Henan Institute of Science and Technology, Xinxiang, , China; Department of Biochemistry, University of Alberta, Edmonton, AB, T6G 2H7, Canada for correspondence: ysliu63@yahoo.ca (Y-S Liu); xjli@ualberta.ca (X-J-Li) References Crean, A. J., Kopps, A. M. and Bonduriansky, R Revisiting telegony: offspring inherit an acquired characteristics of their mother s previous mate. Ecol Lett. 17 (12): Darwin, C The Variation of Animals and Plants under Domestication. John 5

7 Genome Page 6 of 7 Murray, London Darwin, F The Life and Letters of Charles Darwin. John Murray, London Dobzhansky, T Mendelism, Darwinism, and Evolutionism. Proc Amer Phil Soc 109 (4): Fuentes, I., Stegemann, S., Golczyk, H., Karcher, D. and Bock, R Horizontal genome transfer as an asexual path to the formation of new species. Nature 511 (7508): Liu, Y-S Historical and modern genetics of plant graft hybridization. Adv Genet 56: Liu, Y-S Like father like son: a fresh review of the inheritance of acquired characteristics. EMBO Reports 8 (9): Liu, Y-S A new perspective on Darwin s Pangenesis. Biol Rev Camb Philos Soc 83 (2): Liu, Y-S Telegony, the sire effect and non-mendelian inheritance mediated by spermatozoa: a historical overview and modern mechanistic speculations. Reprod Domest Anim 46 (2): Liu, Y-S., Li, X-J Has Darwin s Pangenesis been rediscovered? Bioscience 64 (11): Olby, R. G Charles Darwin s manuscript of Pangenesis. B J History Sci 1 (3): Rechavi, O., Houri-Ze evi, L., Anava, S., Goh, W.S.S., Kerk, S.Y., Hannon, G.J. and Hobert, O Starvation-induced transgenerational inheritance of small RNAs in C. elegans. Cell 158 (2):

8 Page 7 of 7 Genome Roberts, H. F A Darwinian statement of the Mendelian theory. Nature 103 (2598): Singh, R.S Limits of imagination: the 150 th anniversary of Mendel s laws, and why Mendel failed to see the importance of his discovery for Darwin s theory of evolution. Genome, 58 (9):