The Spandrels of San Marco

Adaptation or Drift?

Gould and Lewontin (1979)

• The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme.

• Do not assume that every trait is an adaptation

• Cited more than 4000X

The Cathedral of San Marco

• Are spandrels necessary architectural elements or byproducts of having adjacent arches?

• How many traits of living organisms are spandrels rather than adaptations?

• Organisms are more than collections of traits.

Stephen Jay Gould, 1941-2002, USA

Richard Charles Lewontin, 1929-present, USA

• Empedocles: adaptation does not require a purpose (final cause)

• Aristotle: adaptation requires a purpose• Paley (Natural Theology): organisms perfectly

adapted through design toward a purpose• Lamarck: adaptation through increased

complexity and influence of circumstances• Darwin and Wallace: adaptation is ‘good enough’

outcome of natural selection

Adaptation• Genetic change in

response to changes in habitat (Red Queen Hypothesis)

• Co-adaptations (diversification between insects and flowering plants in Cretaceous)

• Compromise (e.g. sexual selection)

Classic Research on Adaptation• Peter and Rosemary

Grant (1973-present)

• John Arthur Endler (1980)

Genetic Drift

A B O AB United States 42% 10% 45% 3%

Chinese 31% 28% 34% 7%Blackfoot 76% ----- 24% -----

Navajo 24% ----- 76% -----

Genetic Drift in Mice

Genetic drift in inbred mouse colonies happens slowly, subtly, and is difficult to detect and control. It is caused by the same factors (Bailey 1977; Bailey DW. 1982. Immunology Today 3:210-14) that lead to substrain divergence.

Developmental Allometry

Developmental Allometry of Humans

Developmental Allometry of Humans

Khrameeva et al. 2014. Neanderthal ancestry drives evolution of lipid catabolism in contemporary Europeans. Nature Communications. 5:3584 DOI: 10.1038/ncomms4584

Importance of Gould and Lewontin (1979)

• Cited ~4,000X• Functioned as a heuristic• When we examine traits should we assume

that they are adaptations or drift?• G&L (1979) helped to make evolutionary

biology more rigorous.