Hard inheritance

Abstract: The very process of synthesis combines disparate elements into a coherent whole, making complex phenomena more comprehensible as we understand which factors are decisive and, as importantly, which ones less so. Synthesis is a powerful intellectual tool, a beacon that illuminates a wide swath of previously unrelated facts, theories, and even disciplines. In biology in the second quarter of the twentieth century, just such a synthesis between genetics and evolutionary theory flourished through the work of K A. Fisher, Sewall Wright, J. B. S. Haldane, Theodosius Dobzhansky, Ernst Mayr, George Gaylord Simpson, and many, many others. In addition to his crucial scientific work, Mayr made an invaluable organizational contribution through the Society for the Study of Evolution and its journal Evolution (Cain, 1993, 1994, 2000b; Smocovitis, 1992, 1994a, 1994b, 1996). As a historian, he continues to shape how we think about these developments (Mayr & Provine, 1980). As Mayr explains it, The term "evolutionary synthesis" was introduced by Julian Huxley in Evolution: The Modern Synthesis (1942) to designate die general acceptance of two conclusions: gradual evolution can be explained in terms of small genetic changes ("mutations") and recombination, and the ordering of this generic variation by natural selection; and the observed evolutionary phenomena, particularly macroevolutionary processes and speciation, can be explained in a manner that is consistent with the known genetic mechanisms. (Mayr & Provine, 1980, p. 1) Further, of all evolutionary theories, only neo- Darwinism or synthetic theory - as opposed to saltationism (evolution by sudden leaps), Geoffroyism (evolution under direct influence of the environment), orthogenesis (evolution by an organism's built-in tendency toward perfection or progress), or even Darwinism - combines both population thinking (an appreciation for variation as opposed to "essentialism") and a commitment to hard inheritance (Mayr 8c Provine, 1980, p. 4). Forging this synthesis required "bridge builders," geneticists who had experience with natural populations and naturalists who had absorbed the work of the geneticists. Botany posed its own problems. Mayr identified at least two: a sharper differentiation than among zoologists between museum-herbarium workers and their counterparts doing field work and "genetic systems in plants tend to be a good deal more complicated than those of . . . animal groups," which in turn "prevented unanimity in the adoption of a uniform species concept" (Mayr 8c Provine, 1980, p. 137). The result was that "in the 1930s and 1940s no botanist published a book comparable in impact to the books of Dobzhansky, Huxley, Mayr, Rensch, Simpson, or other architects of the synthesis." It would fall to G. Ledyard Stebbins's Variation and Evolution in Plants (1950) to fill that niche. And even then, in 1963, Mayr wrote, "Each of the kingdoms has its own evolutionary peculiarities and these must be worked out separately before a balanced synthesis can be attempted" (Mayr, 1963, p. v). This comment was a partial explanation of why his book of that year was titled Animal Species and Evolution; he, at that point, had 35 years of field and laboratory experience with animal species, but "Lacking a similar familiarity with plants, I might have come up with absurd generalizations if I tried to apply my findings to plants" (Mayr, 1963, p. v). As illuminating as Mayr's perspective on the synthesis is, it cast shadows, leaving some things less clear. The bright beacon washes out some of the nuances and subtleties of lived experience. Edgar Anderson, as an interested participant, used a review of Dobzhansky's Evolution, Genetics, and Man to keep some of those nuances, what he called "odd noises," on the table: In personal conversation Professor Dobzhansky has sometimes chided scholars who, like this reviewer, cherish a Batesonian interest in those few significant facts which do not fit easily with today's facile exposition of basic principles. …

Abstract: 1786–1848 British physician and anthropologist who developed a model of human racial formation based on sexual selection and ideas of beauty. Keywords: hard inheritance; geographical distribution; sexual selection; Blumenbach

Abstract: In the last decade researchers have produced immense amounts of genetic data resulting in many sequenced genomes. Although we may now know the DNA sequence in a genome, just as seeing all the letters of a book, deciphering which sequences encode genes, let alone understanding which combination of genes are required to organize life, is like decoding the meaning of a book written in a language never before seen. Moreover, how does a cell know which genes to turn on and which to turn off? How does a cell control differentiation into various tissues? For this a cell has to know where it comes from (memory) and what to do (encoded by the DNA). So, how does cellular memory exist and how is it transmitted to the next cell after each cell division? What happens if there is a failure in the transmission of that memory? Can such a memory even be transmitted to the next generation of an organism? This last question is very important since it raises the question as to whether our lifestyle affects our children and grand-children. All these questions are currently being addressed in the research field called “epigenetics.” In recent years, epigenetics has rapidly expanded into all biological disciplines but with numerous, different definitions of what epigenetics is. Therefore, it is not easy for students and advanced researchers to find a good entry point in this complex, albeit fascinating subject. This is where the book by Olga and Igor Kovalchuk comes into play. It is one of the first books to broadly discuss all the different aspects and mechanisms of epigenetics. The book begins with a historical perspective starting in the beginning of the nineteenth century that proceeds to today providing an overview of how the ideas about epigenetics have evolved, as well as addressing issues that remain controversial. The historical perspective focuses on theories first proposed by Jean-Baptiste Lamarck, whose ideas Charles Darwin did not completely reject, providing a good assessment of how scientists were thinking and debating at that time (Read a free excerpt from the book: http://www.ftpress.com/articles/article.aspx?p=1896675). Next, the authors discuss the molecular pathways involved in epigenetics. In these chapters the authors provide mechanistic details along with excellent graphics to discuss the most recent aspects of chromatin remodeling, DNA methylation, histone modifications and non-coding RNAs. However, the book does not discuss less obvious examples considered as “epigenetic” phenomena by some researchers, such as modifications caused by prions. After describing epigenetics at the molecular level, the authors explain transgenerational effects mediated by epigenetic mechanisms and different health related subjects, such as the failure of proper transmission of epigenetic memory being associated with cancer and the interesting roles of epigenetics within the context of neuroscience. This chapter connects epigenetics and health with a focus on diet and toxicology, or stated more directly: our lifestyle. Here they summarize how our environment and diet directly impinge on our epigenome, implying that we may not only transmit altered epigenomes affecting the next generation, but that altered epigenomes may more immediately impact our own health. To discuss these aspects the book covers several examples of inheritance of stress memory across generations. The last chapter of the book covers technical applications of RNA silencing [or RNA interference (RNAi)], a very efficient method to silence gene expression by providing small interfering RNAs homologous to the gene to be silenced, which is useful if one cannot just remove a gene. Interestingly, although the book's title indicates a primary focus on the role of epigenetics in health and disease, which is indeed covered, an underlying strength is the broad discussion covering the different roles of epigenetics in numerous organisms, including plants. This approach benefits the reader by providing the background relevant to the actual discovery and the major developments in the field. This approach reflects the expertise and competencies of the authors, both of whom are medical doctors and currently perform basic plant and cancer research. While the title of the book could have been more general to attract a broader audience, it is a great read for anyone interested in epigenetics. A very useful resource for readers involved in teaching are the “Exercises and Discussion Topics” section at the end of each chapter. This allows the reader to reflect on the content and is a good starting point for exercises with students. Also, information boxes give further details and definitions about selected topics. This book is a must for any library located in institutions involved in molecular biology. So, is Lamarck now returning to favor? Perhaps his theories regarding the “inheritance of acquired characteristics” might now indeed be explained by epigenetic mechanisms. However, Lamarck saw this as a sole method of transmitting information from one generation to another, which remains in contrast to the inheritance of genetic (hard inheritance) and epigenetic (soft inheritance) information between generations. Thus, Lamarck's main contribution, aside of his concepts of biological evolution, remain limited to being the first to formulate the idea that “transmission of influential circumstances of life” to the progeny can occur. A very interesting question to address in the future will be to determine if the transition from soft to hard inheritance actually takes place. The book can be found here: http://www.ftpress.com/store/epigenetics-in-health-and-disease-9780132789998

Abstract: Question: How can we measure the effects of exogenous environment in the parental generation on heritable changes in subsequent generations? Mathematical method: Parent–offspring regression models can be used to estimate additive genetic effects that are caused by environmentally alterable signals. Key assumption: To be relevant, environmentally alterable additive effects (e.g. environmentally induced epigenetic changes in cytosine methylation or chromatin formation) must be non-negligible compared with direct additive genetic effects. Predictions: Large environmentally alterable additive genetic variance confounds prediction of evolutionary trajectories, but (1) provides a mechanism by which environmental variance directly increases additive genetic variance, (2) implies that environmental variance can cause evolutionary novelty, (3) provides one of possibly many mechanisms underlying phenotypic plasticity, and (4) may provide an explanation for why plants are more phenotypically plastic than animals. Conclusion: Environmentally alterable additive genetic effects place molecular epigenetic effects and soft inheritance within a modern neo-Darwinian quantitative genetic framework.