Spandrel (biology)

Spandrel (PSF)

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Spandrel (biology) refers to a concept in evolutionary biology that deals with the features of an organism that arise as byproducts of the evolution of other features, rather than due to direct adaptive selection. The term was borrowed from architecture by Stephen Jay Gould and Richard Lewontin in their influential 1979 paper, "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme". In architecture, a spandrel is the space between two arches or between an arch and a rectangular enclosure. In the context of biology, spandrels are characteristics that did not arise independently but as a consequence of the evolution of other structures.

Origin and Usage

The concept of the spandrel in biology was introduced to critique the adaptationist view of evolution, which posits that most traits in an organism have a direct evolutionary advantage. Gould and Lewontin argued that not all traits are adaptive; some may be incidental. For example, the human chin may be considered a spandrel, arising as a structural byproduct of the face's architecture rather than for a specific adaptive function.

Examples

Several examples of biological spandrels have been proposed since Gould and Lewontin's original paper. These include:

• The human chin, as mentioned, which may not serve a specific adaptive function but is a result of the rest of the facial structure.
• The belly button (navel), which is a byproduct of the umbilical cord and not a feature that evolved through natural selection.
• Certain behaviors and cognitive traits, such as reading and writing, which may not have evolved directly through natural selection but as byproducts of the brain's overall capacity for complex tasks.

Criticism and Debate

The concept of spandrels has been both influential and controversial within evolutionary biology. Critics argue that it can be difficult to distinguish between traits that are true spandrels and those that have unrecognized adaptive value. Furthermore, some evolutionary biologists contend that the concept has been overused, leading to a dismissal of the possibility that certain traits may have unknown adaptive functions.

Impact on Evolutionary Theory

Despite criticisms, the concept of spandrels has had a significant impact on evolutionary theory, encouraging a more nuanced view of how traits evolve. It has highlighted the importance of considering the architectural constraints and byproducts of evolution, alongside direct adaptation, in the development of an organism's phenotype.

See Also

• Adaptation
• Evolutionary biology
• Phenotype
• Stephen Jay Gould
• Richard Lewontin

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