Spandrels are architectural elements that develop not through the intention of the architect, but as a consequence of objective, e.g. geometric. Pendentives are given as a special case of spandrels in evolutionary literature; these are spherical triangular areas permitting the placing of a circular dome over a square room. The best known case (at least for evolutionary biologists) consists in the pendentives in the Basilica of St. Mark in Venice. At the present time, these pendentives bear pictures of the four evangelists and thus seem to be an essential and intentionally created element of the artistic decoration of the cathedral. In actual fact, they were not created to bear these paintings, but because this was the most rational structural solution for joining a four-walled base with its cupola ceiling. It is typical that the pendentives in the Basilica of St. Mark acquired an adaptive significance, i.e. that mosaics of four evangelists were placed on them later, several centuries after the creation of the basilica. Many biological structures, even highly organized structures with a highly favourable effect for the survival of the organism, are in fact spandrels, not adaptations.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more