The realization that body parts of animals and plants can be recruited or coopted for novel functions dates back to, or even predates the observations of Darwin. S.J. Gould and E.S. Vrba recognized a mode of evolution...The realization that body parts of animals and plants can be recruited or coopted for novel functions dates back to, or even predates the observations of Darwin. S.J. Gould and E.S. Vrba recognized a mode of evolution of characters that differs from adaptation. The umbrella term aptation was supplemented with the concept of exaptation. Unlike adaptations, which are restricted to features built by selection for their current role, exaptations are features that currently enhance fitness, even though their present role was not a result of natural selection. Exaptations can also arise from nonaptations; these are characters which had previously been evolving neutrally. All nonaptations are potential exaptations. The concept of exaptation was expanded to the molecular genetic level which aided greatly in understanding the enormous potential of neutrally evolving repetitive DNA—including transposed elements, formerly considered junk DNA—for the evolution of genes and genomes. The distinction between adaptations and exaptations is outlined in this review and examples are given. Also elaborated on is the fact that such distinctions are sometimes more difficult to determine; this is a widespread phenomenon in biology, where continua abound and clear borders between states and definitions are rare.展开更多
Dear Editor,External cytokines produced by cells of the innate immune system induce the dif-ferentiation of CD4+T cells into helper T cell subsets with distinct functions and cytokine profiles.Apart from TH1 and TH2 c...Dear Editor,External cytokines produced by cells of the innate immune system induce the dif-ferentiation of CD4+T cells into helper T cell subsets with distinct functions and cytokine profiles.Apart from TH1 and TH2 cells a third subset of helper T cells has been described,which is characterized by increased expression of IL-17A,IL-17F,IL-21 and IL-22(TH17 cells).展开更多
文摘The realization that body parts of animals and plants can be recruited or coopted for novel functions dates back to, or even predates the observations of Darwin. S.J. Gould and E.S. Vrba recognized a mode of evolution of characters that differs from adaptation. The umbrella term aptation was supplemented with the concept of exaptation. Unlike adaptations, which are restricted to features built by selection for their current role, exaptations are features that currently enhance fitness, even though their present role was not a result of natural selection. Exaptations can also arise from nonaptations; these are characters which had previously been evolving neutrally. All nonaptations are potential exaptations. The concept of exaptation was expanded to the molecular genetic level which aided greatly in understanding the enormous potential of neutrally evolving repetitive DNA—including transposed elements, formerly considered junk DNA—for the evolution of genes and genomes. The distinction between adaptations and exaptations is outlined in this review and examples are given. Also elaborated on is the fact that such distinctions are sometimes more difficult to determine; this is a widespread phenomenon in biology, where continua abound and clear borders between states and definitions are rare.
文摘Dear Editor,External cytokines produced by cells of the innate immune system induce the dif-ferentiation of CD4+T cells into helper T cell subsets with distinct functions and cytokine profiles.Apart from TH1 and TH2 cells a third subset of helper T cells has been described,which is characterized by increased expression of IL-17A,IL-17F,IL-21 and IL-22(TH17 cells).
