There is a mature literature on evolution and aging intended to explain how, despite selection for the morphological, metabolic, physiological, and behavioral prerequisites for survival and procreation, with the passage of time bodies deteriorate ultimately resulting in death. The focus of such explanations is typically on concepts such as age-related variation in the potency of selection and the related notion of antagonistic pleiotropy (Fabian and Flatt, 2011), by which suggests that genes able to promote survival and reproductive success in youth may increase loss of function with age. These concepts address selection on intact organisms. In contrast, a recent article in Science (Goodell and Rando, 2015) contains an article addressing the role of selection directly on somatic cells and in particular tissue-specific stem cells. (more…)
Epistasis in Adaptive versus Stochastic Evolution of the Influenza A Virus Nucleoprotein Gene
Epistasis refers to the influence of one genomic mutation or variant on the phenotypic effects of another mutation or variant. Based on available evidence and theory, this phenomenon has a major influence on evolutionary trajectories for organisms of all sorts. The role of epistasis has been studied primarily in the context of adaptive evolutionary change. In a recent paper (2014), Gong and Bloom attempt to determine the relative frequencies of epistatic interactions in adaptive versus stochastic evolution, i.e. evolution driven by selection as opposed to evolution resulting from random processes without a significant selective ‘pressure.’ Gong and Bloom perform this comparison by analyzing homologous nucleoprotein (NP) genes in human and swine influenza A viruses. The authors argue that the human viruses are subject to substantially more intense selection than the swine viruses since domestic swine are much shorter lived and their viruses are not as likely to be subjected to immune memory responses. (more…)
Species-Specific Variation in Molecular Mechanisms of Host Defense Against and Virulence of Toxoplasma gondii
Toxoplasma gondii is an intracellular protozoan parasite that infects many different vertebrate species asexually and undergoes a sexual cycle after infecting cats (http://www.cdc.gov/parasites/toxoplasmosis/, 2013). Parasite oocysts are potentially introduced into the human environment in cat feces. T. gondii is of interest in clinical medicine because humans can serve as accidental intermediate hosts when they ingest oocysts in, for example, undercooked, contaminated meat or ingest parasites in contaminated drinking water. Mother-to-child transmission can also occur. In most healthy individuals the infection does not cause illness, but in individuals with immune deficiencies and in fetuses it can cause substantial morbidity. In the case of congenital infection of a fetus, morbidity, including vision loss, cognitive deficits, and seizures tends to be more severe with earlier infection and mortality can result in either miscarriage or stillborn birth. L. David Sibley (Washington University) and colleagues (Etheridge et al., 2014) have now further clarified the molecular basis for the variation in virulence among different T. gondii lineages for mice, an important prey species for cats and therefore an important intermediate host species. (more…)
The Future of the “Selfish Gene” Metaphor
This past December, science writer David Dobbs published an essay (2013) in the online magazine Aeon (aeon.co/magazine/) that purports to explain why the ‘selfish gene’ concept is outmoded and should be retired. It elicited a good deal of commentary, and in early March, Aeon published responses (Sapolsky et al., 2014) to the original article from four individuals (two scientists, a genetic counselor, and a philosopher) as well as additional comments by Dobbs. For those who are interested in this controversy, responses to the original Dobbs article were also posted elsewhere by Richard Dawkins (2013) and Jerry Coyne (2013a, b). Below, I provide a sense of the arguments of Dobbs, the tenor of the criticisms of Dobbs’s piece, and selected other critiques of the gene-centric approach to evolution. (more…)
An Evolutionary Link between Cancer and Scleroderma: Somatic Cell Variation and Selection
Geneticists have recognized for some time that many genes exhibit pleiotropy, meaning that one mutation can manifest in two or more distinguishable phenotypic effects. In a fascinating study recently published in Science [2014 Jan 10;343(6167):152-7. doi:10.1126/science.1246886], Joseph et al. offer evidence for an example of pleiotropy in which the distinct phenotypic effects associated with mutation of the POLR3A gene, which encodes a subunit (RPC1) of RNA polymerase III, are associated with two different diseases: one or another form of cancer and an autoimmune disease (scleroderma). (more…)