Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: Small changes, big results: evolution of morphological discontinuity in mammals. | Journal of Biology BioMed Central Minireview Small changes big results evolution of morphological discontinuity in mammals Rodney L Honeycutt Address Natural Science Division Pepperdine University Malibu California 90263-4321 USA. Email Published 18 March 2008 Journal of Biology 2008 7 9 doi jbiol71 The electronic version of this article is the complete one and can be found online at http content 7 3 9 2008 BioMed Central Ltd Abstract Comparative morphological and developmental studies including a recent comparative study of tooth development among the Afrotherian mammals are indicating the types of genetic mechanisms responsible for the evolution of morphological differences among major mammalian groups. The orders of eutherian mammals are especially characterized by morphological differences in the skull and dentition related to different requirements for processing food and in the postcranial skeleton which is adapted for varied modes of locomotion. The evolutionary biologist George Gaylord Simpson 1 defined major morphological discontinuities among higher taxa specifically the orders of mammals as the result of macroevolution or quantum evolution . In many cases these discontinuities lack fossil evidence of transitions appearing as what Simpson termed breaks in the fossil record and thus probably result from major adaptive shifts. Along with the accepted processes of microevolu-tionary change at the population level Simpson also suggested that mutations with large phenotypic effects unquestionably provide a theoretically excellent mechanism for large changes in morphology. These discontinuities as well as the short time periods associated with the diversification of many mammalian orders are still presenting a challenge to paleontologists geneticists and developmental biologists attempting to reconstruct the Mammal Tree of Life a first step in understanding the geological and biological processes that are .
