Download 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 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
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/ncomms4584
NLS= Neanderthal-like sites
GW= Genome wide
LCP= Lipid Catabolism Protein
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.