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Traditional Explanations (traditional + explanation)
Selected AbstractsFemale post-reproductive lifespan: a general mammalian traitBIOLOGICAL REVIEWS, Issue 4 2004Alan A. Cohen ABSTRACT Traditional explanations for the evolution of menopause and post-reproductive lifespan in human females have been based on the benefits of maternal or grand-maternal care outweighing the cost of lost reproduction. These explanations assume an evolutionary origin of menopause since human divergence with the most recent common ancestor. In this study, I conduct a literature survey of studies of 42 mammal species from eight orders, showing that post-reproductive lifespan appears to be widespread among mammals. I then propose an alternative to traditional hypotheses: following accepted theories of trade-offs and senescence, I suggest that the cost of extending reproductive lifespan might be relatively high in female mammals. Somatic and reproductive senescence appear to follow separate trajectories, so it is not surprising that the two processes should occur on different schedules. The timing of each process is probably determined by maximization of reproductive performance and survival early in adulthood, with consequent trajectories resulting in a post-reproductive lifespan. The early end of reproduction relative to lifespan may be due to the cost of production and/or maintenance of oocytes, which decline exponentially over time. Oocyte number below a threshold may trigger an end to normal hormonal cycling. [source] Global warming, Bergmann's rule and body mass , are they related?JOURNAL OF ZOOLOGY, Issue 4 2002The chukar partridge (Alectoris chukar) case Abstract Using museum specimens collected in Israel during the second half of the 20th century, no support was found for the hypothesis that body mass and tarsus length of chukar partridges Alectoris chukar has changed as a result of global warming. Body mass showed fluctuations during the year, reaching a maximum in late winter and spring and a minimum in summer. Bergmann's rule predicts that in warm-blooded animals, races from warm regions will be smaller than races from colder regions, and a wider explanation states that body size is positively related to latitude. Because of its topography and varied climate, Israel provides a unique opportunity to separate partly the effect of latitude from that of ambient temperature, thus testing if Bergmann's rule is related to latitude or to climatic variables. We found that body mass (and marginally also tarsus length) declined significantly with decreasing latitude in accordance with the wider explanation of Bergmann's rule, but ambient temperature explained a much smaller fraction of the variation in body mass than latitude. These results weaken the traditional explanation to Bergmann's rule that a heat conservation mechanism causes the latitudinal size variation. [source] WHY DOES A TRAIT EVOLVE MULTIPLE TIMES WITHIN A CLADE?EVOLUTION, Issue 1 2006REPEATED EVOLUTION OF SNAKELINE BODY FORM IN SQUAMATE REPTILES Abstract Why does a trait evolve repeatedly within a clade? When examining the evolution of a trait, evolutionary biologists typically focus on the selective advantages it may confer and the genetic and developmental mechanisms that allow it to vary. Although these factors may be necessary to explain why a trait evolves in a particular instance, they may not be sufficient to explain phylogenetic patterns of repeated evolution or conservatism. Instead, other factors may also be important, such as biogeography and competitive interactions. In squamate reptiles (lizards and snakes) a dramatic transition in body form has occurred repeatedly, from a fully limbed, lizardlike body form to a limbreduced, elongate, snakelike body form. We analyze this trait in a phylogenetic and biogeographic context to address why this transition occurred so frequently. We included 261 species for which morphometric data and molecular phylogenetic information were available. Among the included species, snakelike body form has evolved about 25 times. Most lineages of snakelike squamates belong to one of two ecomorphs, either short-tailed burrowers or long-tailed surface dwellers. The repeated origins of snakelike squamates appear to be associated with the in situ evolution of these two ecomorphs on different continental regions (including multiple origins of the burrowing morph within most continents), with very little dispersal of most limb-reduced lineages between continental regions. Overall, the number of repeated origins of snakelike morphology seems to depend on large-scale biogeographic patterns and community ecology, in addition to more traditional explanations (e.g., selection, development). [source] Nitric Oxide and the Paranasal SinusesTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 11 2008Jon O. Lundberg Abstract The discovery within the paranasal sinuses for the production of nitric oxide (NO) has altered the traditional explanations of sinus physiology. This review article reports the ongoing investigation of sinus physiology beginning with the discovery of NO gas production in the paranasal sinuses that occurred in 1995, and the impact that finding has had both in the basic science and clinical arenas. It was shown that healthy paranasal sinus epithelium expresses an inducible NO synthase that continuously generates large amounts of NO, a pluripotent gaseous messenger with potent vasodilating, and antimicrobial activity. This NO can be measured noninvasively in nasally exhaled breath. The role of NO in the sinuses is likely to enhance local host defense mechanisms via direct inhibition of pathogen growth and stimulation of mucociliary activity. The NO concentration in a healthy sinus exceeds those that are needed for antibacterial effects in vitro. In patients with primary ciliary dyskinesia (PCD) and in cystic fibrosis, nasal NO is extremely low. This defect NO generation likely contributes to the great susceptibility to chronic sinusitis in these patients. In addition, the low-nasal NO is of diagnostic value especially in PCD, where nasal NO is very low or absent. Intriguingly, NO gas from the nose and sinuses is inhaled with every breath and reaches the lungs in a more diluted form to enhance pulmonary oxygen uptake via local vasodilation. In this sense NO may be regarded as an "aerocrine" hormone that is produced in the nose and sinuses and transported to a distal site of action with every inhalation. Anat Rec, 291:1479,1484, 2008. © 2008 Wiley-Liss, Inc. [source] Neither Hybrid nor Unique: A Reinterpretation of the East Asian Welfare RegimeASIAN SOCIAL WORK AND POLICY REVIEW, Issue 3 2008Kyung-Zoon Hong Some researchers have been convinced that welfare developments in East Asia, especially Japan and Korea, can be fitted into the existing three worlds of welfare model, while others have insisted that existing welfare regime theories are not able to explain East Asian welfare regimes. This article assumes that we need to go beyond both of these traditional explanations. In the welfare state research fields, welfare regime approaches tend to focus on specific contextual conditions and cross-national differences. As a result, they tend to overemphasize history at the expense of theory. This article tries to combine deductive causal modeling with an institutional,historical context by identifying the contingent rent political game model and deducing important characteristics of East Asian welfare regime from this model. This model opens out the possibility of change in East Asian welfare regimes following the processes of democratization and globalization. Details of this are given in the conclusion. [source] | ||||||||||