02/02/2016
Dr Alex Badyaev
Lecture 5
2016
News/Updates:
ECOL 330
Evolution of Animal Form & Function
Epigenesis
1) First Exam: February 16 (Tue)
2) Exam questions will be posted by Feb 11
3) No office hours on Feb 9 (Tue)
Can discuss questions during Feb 11 class
Epigenesis
The gradual and progressive appearance of new structures, each dependent on preceding structures, processes, and environments
Experiments to test his theory that “the sex of individuals was mechanistically determined as a function of the shape of the egg”
“There is only one plan into which all animals fitted
and from which all animals should be derived. And there
are environmental (and physiological) explanations for
deviations from the unity of plans”
Environment directly alters embryonic development
Geoffroy Saint‐Hilaire “I shall request the following for the upcoming
(1772‐1844)
Geoffroy Saint‐Hilaire
(1772‐1844)
military expedition to Egypt:
1820 experiments on manipulating development
600 chicken eggs
— tying the oviducts of the hen to the eggs during incubation
— submerging eggs in water, wax, varying temperature
Incubator
A house to keep hatched chicks
112 pairs of pigeons and 2 houses to keep them
25 ostrich eggs and 10 breeding pairs
Napoleon Bonaparte
Salary for two full-time assistants”
Epigenesis
“Development cannot be preformed or predetermined if
climatic changes evoke structural changes..”
Epigenesis
“How do so many different structures arise
from so seemingly simple a beginning as the
egg?”
Aristotle (384 ‐ 322BC) Fundamental similarities in the development of birds, fish and mammals
 Progressive change over preformation
Aristotle (384 ‐ 322BC) 1
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Epigenesis
The parts of embryos develop from elements that
had no equivalent in adults or in earlier stages,
Epigenesis
e.g., appearance of blood vessels where none existed previously, progressive development of the
tubular gut from a flat plate…
Caspar Friedrich Wolff (1734‐1794) “Biologists therefore gradually returned to the views of
the fathers of embryology, and in the end universally
accepted the fact that development is not a process of
unfolding but one of progressive new-formation or
epigenesis”
1925
“When the formation of the intestine in this
manner has been duly weighed, almost no
doubt can remain, I believe, of the truth of
epigenesis”
1767
Edmund B. Wilson
(1856‐1939)
Form determines function or
function determines form?
Form and Function
structure vs utility, ground plan vs adaptation
“In architecture,
Form follows Function, not
Function follows Form!”
L. Sullivan
Louis Sullivan
(1856-1924)
Carson Pirie Scott Store, 1899
The Auditorium, 1888
Wainwright Building, 1890
“In architecture, form and function are one”.
Frank Lloyd Wright
Louis Sullivan
(1856-1924)
But in biology?
“By his philosophy
“FORM FOLLOWS FUNCTION”,
he summed up all truth in art”
Sullivan’s tombstone in Gracelands Cemetery
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Form and Function
Form and Function
Long tradition in vertebrate morphology of inferring animal function from static form – Cuvier view
Is it form that determines function or function determines form?
Primacy of Function: Function determines form
“Form was imposed by the functional demands of
the environment and that similar forms reflected similar
functional adaptations”
But similarity of their functions cannot explain similarity in arrangements
of bones inside them…
Homology – similarity due to ancestral feature
Georges Cuvier
(1769‐1832)
1799 (30 year old) – 22 volume “Histoire des Poissons”
Founder of palaeontology with a study of living and extant elephants
Analogy – similarity due to similar function
Primacy of Form: Form determines function
“Function emerges as a mere by-product of form”
Geoffroy Saint‐Hilaire
(1772‐1844)
Depending on developmental hierarchy…
Must one study function directly or is it possible to infer function from structure?
Form and Function
Why?
Must one study function directly or is it possible to infer function from structure?
Bat
Mouse
Example of past form constraining current function?
Or an example of primacy of current function over form?
Function 1:
Food access
Current empirical support
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Function 2:
Mate access
Current empirical support
How to distinguish
“form follows function”
from “function follows form”
scenarios? 4