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Traditional Hypotheses (traditional + hypothesis)
Selected AbstractsHeritability of human cranial dimensions: comparing the evolvability of different cranial regionsJOURNAL OF ANATOMY, Issue 1 2009Neus Martínez-Abadías Abstract Quantitative craniometrical traits have been successfully incorporated into population genetic methods to provide insight into human population structure. However, little is known about the degree of genetic and non-genetic influences on the phenotypic expression of functionally based traits. Many studies have assessed the heritability of craniofacial traits, but complex patterns of correlation among traits have been disregarded. This is a pitfall as the human skull is strongly integrated. Here we reconsider the evolutionary potential of craniometric traits by assessing their heritability values as well as their patterns of genetic and phenotypic correlation using a large pedigree-structured skull series from Hallstatt (Austria). The sample includes 355 complete adult skulls that have been analysed using 3D geometric morphometric techniques. Heritability estimates for 58 cranial linear distances were computed using maximum likelihood methods. These distances were assigned to the main functional and developmental regions of the skull. Results showed that the human skull has substantial amounts of genetic variation, and a t -test showed that there are no statistically significant differences among the heritabilities of facial, neurocranial and basal dimensions. However, skull evolvability is limited by complex patterns of genetic correlation. Phenotypic and genetic patterns of correlation are consistent but do not support traditional hypotheses of integration of the human shape, showing that the classification between brachy- and dolicephalic skulls is not grounded on the genetic level. Here we support previous findings in the mouse cranium and provide empirical evidence that covariation between the maximum widths of the main developmental regions of the skull is the dominant factor of integration in the human skull. [source] Correlates of Levels of Democracy in Latin America During the 1990sLATIN AMERICAN POLITICS AND SOCIETY, Issue 2 2006Cynthia McClintock ABSTRACT Does the conventional wisdom about the relationships between economic, cultural, and political party variables and democracy stand up in the Latin American experience of the 1990s? This study, utilizing new data sets for the region, finds that some traditional hypotheses are upheld better than others. It sustains the conventional wisdom that economic development, economic growth, democratic values, and (with a two-year lead) education correlate positively with the level of democracy. Surprisingly, however, neither social trust nor the number of political parties is significantly correlated with the level of democracy. The study suggests various possible explanations for the weak or nonexistent relationships for social trust and number of parties, in the hope that these surprising results will stimulate further research. [source] Timing of sperm transfer in Diacamma pallidumPHYSIOLOGICAL ENTOMOLOGY, Issue 4 2007DIANE ALLARD AbstractDiacamma species (Hymenoptera, Formicidae) differ from other ants by the extremely long duration of copulation. By using histological sections through mating pairs of Diacamma pallidum (F. Smith), it is demonstrated that the transfer of sperm to the female genital tract only takes 2 min and is completed quickly after the onset of copulation, although the male and female will remain connected for many hours. Next to the two traditional hypotheses of mate guarding and mate manipulation commonly invoked to explain prolonged copulations, a new hypothesis is proposed linked to the interference of the nestmate workers with the mating pair, and suggestions for further research are given. [source] Female 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] Phylogenetics of Sigmodontinae (Rodentia, Muroidea, Cricetidae), with special reference to the akodont group, and with additional comments on historical biogeographyCLADISTICS, Issue 4 2003Guillermo D'El, acute;a This is the first cladistic analysis of sigmodontine rodents (Cricetidae, Sigmodontinae) based on nuclear and mitochondrial DNA sequences. Two most parsimonious cladograms (7410 steps in length; CI=0.199; RI=0.523) were discovered. Sigmodontinae appears well supported. Sigmodon is sister to the remaining living sigmodontines. It is shown that Euneomys is not a phyllotine and that the Reithrodon group is not monophyletic. Results corroborate that the abrothricines form a natural group that is not part of the akodont radiation. The akodontine tribe is well supported, and is composed of five main clades, whose limits and relationships are thoroughly discussed. For instance, the scapteromyines do not form a natural group and they fall within the akodontine clade. Additionally, I present some taxonomic judgments and comments on the historical biogeography of sigmodontines in the light of the newly discovered relationships. For example, five akodontine divisions are suggested: the Akodon, the Bibimys, the Blarinomys, the Oxymycterus, and the Scapteromys Divisions. It is shown that traditional hypotheses of sigmodontine historical biogeography are falsified by the recovered topology. [source] Chordate phylogeny and evolution: a not so simple three-taxon problemJOURNAL OF ZOOLOGY, Issue 2 2008T. Stach Abstract Traditional concepts of chordate phylogeny have recently been in turmoil: in a large-scale molecular study, the traditional hypothesis that cephalochordates are sister taxon to craniates was replaced by the hypothesis of a sister group relationship between tunicates and craniates. It was claimed that the morphological evidence that supported traditional phylogeny was weak and that morphological characters at least equally strong could be mustered in support of the ,new phylogeny.' In the present review, it is shown that the uncritical use of published codings of morphological characters in recent phylogenetic analyses is responsible for this perception. To ameliorate this situation, the main focus of the present publication is a review of the morphological evidence that has been deemed relevant in chordate phylogeny. Characters are presented in enough detail to allow readers to make self-reliant informed decisions on character coding. I then analyze these characters cladistically, and it is demonstrated that support of the traditional hypothesis is substantial. I briefly evaluate molecular systematic studies and criticize ,evo-devo' studies for lack of cladistic rigor in the evolutionary interpretations of their data by (1) failing to formally code their characters (2) failing to subject their data to the congruence test with other characters, the crucial test in phylogenetic analyses. Finally, a short and by necessity eclectic discussion of suggested evolutionary scenarios is presented. [source] | ||||||||||