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Evolutionary Paradox (evolutionary + paradox)
Selected AbstractsPERSPECTIVE: GENETIC ASSIMILATION AND A POSSIBLE EVOLUTIONARY PARADOX: CAN MACROEVOLUTION SOMETIMES BE SO FAST AS TO PASS US BY?EVOLUTION, Issue 7 2003Massimo Pigliucci Abstract., The idea of genetic assimilation, that environmentally induced phenotypes may become genetically fixed and no longer require the original environmental stimulus, has had varied success through time in evolutionary biology research. Proposed by Waddington in the 1940s, it became an area of active empirical research mostly thanks to the efforts of its inventor and his collaborators. It was then attacked as of minor importance during the "hardening" of the neo-Darwinian synthesis and was relegated to a secondary role for decades. Recently, several papers have appeared, mostly independently of each other, to explore the likelihood of genetic assimilation as a biological phenomenon and its potential importance to our understanding of evolution. In this article we briefly trace the history of the concept and then discuss theoretical models that have newly employed genetic assimilation in a variety of contexts. We propose a typical scenario of evolution of genetic assimilation via an intermediate stage of phenotypic plasticity and present potential examples of the same. We also discuss a conceptual map of current and future lines of research aimed at exploring the actual relevance of genetic assimilation for evolutionary biology. [source] Comparing fecundity in parthenogenetic versus sexual populations of the freshwater snail Campeloma limum: is there a two-fold cost of sex?INVERTEBRATE BIOLOGY, Issue 1 2009Lisa T. Crummett Abstract. The predominance of sexuality in eukaryotes remains an evolutionary paradox, given the "two-fold cost of sex" also known as the "cost of males." [Correction added after online publication 29 January 2009: in the preceding sentence, extraneous words were deleted.] As it requires two sexual parents to reproduce and only one parthenogenetic parent, parthenogens should have twice the reproductive rate compared with their sexual counterparts and their genes should spread twice as fast, if all else is equal. Yet, parthenogenesis is relatively rare and considered an evolutionary dead-end, while sexuality is the dominant form of reproduction in multicellular eukaryotes. Many studies have explored short-term benefits of sex that could outweigh its two-fold cost, but few have compared fecundity between closely related sexuals and parthenogens to first verify that "all else is equal" reproductively. We compared six fecundity measures between sexual and parthenogenetic populations of the freshwater snail, Campeloma limum, during a brooding cycle (1 year) across two drainages. Drainages were analyzed separately because of a significant drainage effect. In the Savannah drainage, fecundity was not significantly different between sexuals and parthenogens, even though parthenogens had significantly more empty egg capsules per brood. In the Ogeechee drainage, parthenogens had significantly more egg capsules with multiple embryos and more hatched embryos than sexuals. Taken over 1 year, embryo size was not significantly different between parthenogens and sexuals in either drainage. Given these results and the close proximity of sexual and parthenogenetic populations, it is perplexing why parthenogenetic populations have not completely replaced sexual populations in C. limum. [source] Type 2 diabetes, cardiovascular disease, and the evolutionary paradox of the polycystic ovary syndrome: A fertility first hypothesisAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2009Stephen J. Corbett Worldwide, the high prevalence of the Polycystic Ovary Syndrome (PCOS), a heritable cause of ovarian infertility, is an evolutionary paradox, which provides insight into the susceptibility of well-fed human populations to cardiovascular disease and diabetes. We propose that PCOS, Type 2 diabetes (T2D) and the Metabolic Syndrome are modern phenotypic expressions of a metabolic genotype attuned to the dietary and energetic conditions of the Pleistocene. This metabolic "Fertility First" rather than "Thrifty" genotype persisted at high prevalence throughout the entire agrarian period,from around 12,000 years ago until 1800 AD,primarily, we contend, because it conferred a fertility advantage in an environment defined by chronic and often severe seasonal food shortage. Conversely, we argue that genetic adaptations to a high carbohydrate, low protein agrarian diet, with increased sensitivity to insulin action, were constrained because these adaptations compromised fertility by raising the lower bound of body weight and energy intake optimal for ovulation and reproduction. After 1800, the progressive attainment of dietary energy sufficiency released human populations from this constraint. This release, through the powerful mechanism of fertility selection, increased, in decades rather than centuries, the prevalence of a genotype better suited to carbohydrate metabolism. This putative mechanism for rapid and recent human evolution can explain the lower susceptibility to T2D of today's Europid populations. This hypothesis predicts that the increasing rates of diabetes and cardiovascular disease, which typically accompany economic development, will be tempered by natural, but particularly fertility, selection against the conserved ancestral genotypes that currently underpin them. Am. J. Hum. Biol. 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||