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Structure and Function
Structure and Function in the Origin
Structures developed through descent by
modification modulated by natural selection.
Connects structure with function through
adaptation.
Influence of Naturphilosophie
• Archetype or Urplan
• Development of taxa within the plan
Richard Owen
1804-1892, Britain
Following Origin
Determine evolutionary history by morphology
• Similarities and differences between existing
taxa
• Construct phylogenies using paleontology
Thomas Henry Huxley
1825-1895, Britain
Ernst Heinrich Philipp August Haeckel
• German naturalist
• Expert on Radiolaria
• Coined many common terms
including Protista, Ecology,
Phylogeny, Stem Cell
• Developed Darwinism built
on Naturphilosophie
• Evolutionary Morphology:
search for phylogenies based
on form and development
within structural constraints
1834-1919, Germany
H.M.S Challenger
• Supported, in part, by
The Royal Society
• Traveled 170,000 km
samples from the
surface to the bottom
1872-1876
Kunst-Formen der Natur
• Had been populizer
of evolution
• Artist and produced
100 plates in the
form of Art Nouveau
• Common ancestry
explained repeated
patterns in body
plans
Following the rediscovery of Mendel and the
discovery of mutations, structural change due to
random mutation forming hopeful monsters.
Structural constraints not as important.
Theodosius Grygorovych Dobdzansky
• Initially, mutationist
• Then, began to work
on ADH in fruitflies.
– Enough natural
variation
– Natural selection
documented in fruitflies
1900-1975, Russian
Empire and USA
From Michael Ruse (2003)
Now understand that living things have
evolved within multiple constraints (as
did Darwin):
• Genetic constraints:
– Does the gene produce product(s)?
– Size of genome
• Historical or phylogenetic
constraints
• Structural constraints: the task of
putting together a functioning
organism
1940-present, USA
Genetic Constraints
• Product(s) of the
gene
– Working product(s)
– Pleiotropy
• Size of genome
– Related to complexity
– Can determine size of
the cell
Rudolf Raff,
1941- present,
USA
Historical Constraints
• Developmental constraints; earlier molecular characters fixed in
the line
– Need not be optimally adaptive
– Homologies based on past history
– Homeotic genes
• Proteins that regulate structural genes
• HOX genes (homologs in fruit flies, frogs, fish, mice, and humans)
• Relationship between bauplan (urplan) and adaptation
– Might be nonadaptive or maladaptive
– Reduce importance of function in evolution
Structural Constraints
• Many
characters are
left over or
allometric (ex:
Irish Elk).
• How do new
characters
form?
• Unexpected
structures can
be co-opted
(ex: feathers).
D’Arcy Wentworth Thompson
• On Growth and
Form (1916)
• Form over function
• Form determined
by physics of the
environment (ex:
aquatic organisms
conform to a waterdrop shape)
• Thus, physics
trumps adaptation
1860-1948, Scotland
Radiolarian Evolution, Form and Function
• Recognized as unicell
with mineralized nested
cytoskeleton elements
• 2 Major groups: SiO2
and SrSO4
• Both have taxa that are
bilaterally- or radiallysymmetrical
Structure and Function
• Molecular phylogenetics
• Molecules have form that is related to function
• Confirms relationship Darwinian relationship between form and
function thus connecting form to adaptation (natural selection)
ML phylogeny
based on SSU
rRNA
…natural selection has been invigorated and
made healthier precisely because of the new
emphasis on form, rather than despite it.
-Michael Ruse