The Spandrels of San Marco Adaptation or Drift

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 4000 X

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, 19412002, USA Richard Charles Lewontin, 1929 -present, USA

Evolution of Adaptation • Empedocles (Agrigentum, 495 -430 BCE): adaptation does not require a purpose (final cause) • Aristotle (Stagira, 384 -322 BCE): adaptation requires a purpose • Paley (Natural Theology, UK, 1743 -1805): organisms perfectly adapted through design toward a purpose • Lamarck (France, 1744 -1829): adaptation through increased complexity and influence of circumstances • Darwin (UK, 1809 -1882) and Wallace (UK, 1823 -1913): adaptation is ‘good enough’ outcome of natural selection

Addressing Adaptationism Dr. Pangloss (Voltaire’s Candide) “Things cannot be other than they are… Everything is made for the best purpose. Our noses were made to carry spectacles, so we have spectacles. Legs were clearly intended for breeches, and so we wear them. ”

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) Darwin’s finches • John Arthur Endler (1980) Guppies

Sources of Genetic Drift Stochastic drift of alleles in a reduced breeding population • Genetic Bottleneck: reduction of population, usually by some catastrophic or random event • Founder Effect: a small subpopulation becomes reproductively isolated from the larger population

Genetic Drift: Importance of Population Size A B O AB United States 42% 10% 45% 3% Chinese 31% 28% 34% 7% Blackfoot 76% ----- 24% ----- Navajo 24% ----- 76% -----

Genetic Bottleneck

Bottleneck in Prairie Chickens

Human Bottleneck

Founder Effect

Polydactyly in Amish Populations

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: Size Matters

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/ncomms 4584 NLS= Neanderthal-like sites GW= Genome wide LCP= Lipid Catabolism Protein

Importance of Gould and Lewontin (1979) • Cited ~4, 000 X • 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.