Spandrel (biology)

The term Spandrel (English for Spandrille, Archenzwickel ) as a name for an evolutionary biological phenomenon was coined in 1979 by Stephen Jay Gould and Richard C. Lewontin .

The term comes from architecture, where it describes a decorated area between a round arch and its rectangular border. Gould uses these structural features as a metaphor for biological phenomena: he uses them to describe properties of phenotypes which , according to his theory, have arisen as by-products of true adaptation in the course of evolution.

Gould is of the opinion that spandrels arose as a non - adaptive by-product of structural optimization ( primary cause ) but then proved useful for supporting decorative elements ( secondary effect ). They were therefore retained even after the further development of other load-bearing structures made them statically superfluous.

As an example from nature it can be cited that in some land snails the umbilicus , a cylindrical cavity that is created during spiral shell growth, is used as a breeding chamber. The argument here is that the umbilicus did not originally develop for the purpose of being used as a breeding chamber, but is a geometrically necessary by-product of housing growth ( primary cause ), which (by chance) has proven useful for protecting the eggs ( secondary effect ) and has therefore been retained in this function in some species, while in other species that do not need this protection it is completely closed by calcite (one then speaks of a columella ).

The theory of spandrel as a non-adaptive by-product was criticized by Daniel Dennett (1995). The design of the gussets is not without an alternative, and their specific appearance has the special function of carrying decorative elements.

literature

Stephen Jay Gould , Richard C. Lewontin : The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Program . In: Proceedings of the Royal Entomological Society of London. Series B: Taxonomy. Vol. 205, No. 1161, 1979, ISSN 0375-0434 , pp. 581-598.
Stephen Jay Gould: The exaptive excellence of spandrels as a term and prototype . In: Proceedings of the National Academy of Sciences . Vol. 94, No. 20, 1997, ISSN 0027-8424 , pp. 10750-10755.

Individual evidence

^ Daniel C. Dennett : Darwin's Dangerous Idea. Evolution and the Meanings of Life. Simon & Schuster, New York, NY et al. 1995, ISBN 0-684-80290-2 , chapter 10.

[1] Daniel C. Dennett : Darwin's Dangerous Idea. Evolution and the Meanings of Life. Simon & Schuster, New York, NY et al. 1995, ISBN 0-684-80290-2 , chapter 10.