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In evolutionary biology, a spandrel is a phenotypic characteristic that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection. The term originated during the Roman era as an architectural word for the roughly triangular space between the tops of two adjacent arches and the ceiling. These spaces were not actually utilized until later on, when artists realized they could make designs and paint in these small areas, enhancing the overall design of the building. Stephen Jay Gould, a paleontologist at Harvard, and Richard Lewontin, a population geneticist, borrowed the word to apply to secondary byproducts of adaptations that were not necessarily adaptive in themselves. ==Origin of the term== The term was coined by the Harvard paleontologist Stephen Jay Gould and population geneticist Richard Lewontin in their influential paper "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme" (1979). In their paper, Gould and Lewontin employed the analogy of spandrels in Renaissance architecture: curved areas of masonry between arches supporting a dome that arise as a consequence of decisions about the shape of the arches and the base of the dome, rather than being designed for the artistic purposes for which they were often employed. The authors singled out properties like the necessary number of four and their specific three-dimensional shape. At the time, it was thought in the scientific community that everything an animal has developed that has a positive effect on that animal’s fitness was due to natural selection or some adaptation. Gould and Lewontin proposed an alternative hypothesis: that due to adaptation and natural selection, byproducts are also formed. These byproducts of adaptations that had no real relative advantage to survival, they termed spandrels. In the biological sense, a "spandrel" or "exaptation" (as Gould and Lewontin referred to them) might result from an architectural requirement inherent in the ''Bauplan'' of an organism, or from some other constraint on adaptive evolution. Evolutionary biology uses the term spandrel for features of an organism arising as byproducts, rather than adaptations, that have no clear benefit for the organism's fitness and survival. Gould and Lewontin rebuted certain counter-arguments, which stated that spandrels were just small unimportant byproducts, but stated that, "we must not recognize that small means unimportant. Spandrels can be as prominent as primary adaptions" (Gould and Lewontin). A main example used by Gould and Lewontin is the example of the human brain. It is explained that the human brain is the area in humans that is thought to have the most spandrels. So many secondary processes and actions come in addition to the human brain and its main functions. These secondary processes and thoughts are the spandrels of the human body, which eventually through thought and action can turn into an adaption or fitness advantage to humans. Just because something is a secondary trait or byproduct of an adaption does not mean it has no use because it may eventually be used as something beneficial to the animal. Gould’s and Vrba’s (1982) theory of exaptation,〔 〕 named as "exaptations" those characteristics that enhance fitness in their present role but were not built for this role by natural selection. Exaptations may be divided into two subcategories; preadaptation and spandrels. Spandrels are characteristics that did not originate by the direct action of natural selection and that were later co-opted for a current use. Gould saw the term to be optimally suited for evolutionary biology for "the concept of a nonadaptive architectural by-product of definite and necessary form – a structure of particular size and shape that then becomes available for later and secondary utility". (Gould 1997) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spandrel (biology)」の詳細全文を読む スポンサード リンク
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