Botany 940
Evidence for
evolution
Homology/Analogy
Natalia Alvarez
Kevin Coleman
2006
Homolog structure:
Similar structure and
position, but different
function
Courtesy of Prof. Ken Sytsma
http://evolution.berkeley.edu
Analog structure:
Similar function, but
different origin
Homology
Courtesy of Prof. Ken Sytsma
How can we explain this?
Hypotheses??
Homology
• Archetypal explanation
“The same organ in different
animals under every variety
of form and function.”
(Owen,1843)
• Common ancestry
“A structure is similar among
related organisms because
those organisms have all
descended from a common
ancestor that had an
equivalent trait. “
(Darwin,1859)
Homology in character evolution. Staton, July 2000
Wells’ Critique: Circular definition
Homology/Common ancestor
“Features are homologous because they are
inherited from a common ancestor”
Common ancestry is inferred using homologous
features.
•Features can be tested by “Multiple ad hoc
hypothesis of homology” (Kluge 1997)
Origin of arthropod compound eye. Oakley,2002.
How would you test common
ancestry?
How would you test common
ancestry?
• Fossil record
– Structure and position
– behavioral patterns
• Fossil record
-Fossil intermediates
– Behavioral patterns
Bird
Alligator
Dinosaur
How would you test common
ancestry?
• Fossil record
– Structure and position
– behavioral patterns
• Genetics
Wells’ Critique: Genetics
• Assumption: homologous features are
programmed by similar genes
• Problems
1. Similar genes determine radically different
structures.
2. Organisms with different genes produce
similar structures.
Example: Pax6 in fruit flies, mice and humans
• Genetics: Homolog structures and genes
Is there a correlation between genotype and
phenotype?
Pax6 in fruit flies, mice and humans:
"master regulator of eye development“ (qtd. in Displan,1997).
Downstream genes are not the same, thus determines
different structures.
http://big.big.or.jp/~mastakeu/pax6.html
http://www.umich.edu/~mmgmed/faculty/glaser/glaser2-resprojects.html
How would you test common
ancestry?
• Fossil record
– Structure and position
– behavioral patterns
• Genetics
• Developmental pathways
Wells’ Critique: Developmental
Pathways
• Assumption: homologous
features should develop
in similar ways
• Problems
1. Similar pathways may
produce very dissimilar
features.
2. Similar features are often
produced via very
different pathways.
Haeckel’s drawings
Gilbert, S. F. 1997. http://7e.devbio.com/about.php
• Developmental pathways: shared features,
shared early developmental features ,presence
and sequence of development stages.
http://www.natcenscied.org/icons/icon4haeckel.html
How would you test common
ancestry?
• Fossil record
– Structure and position
– behavioral patterns
• Genetics
• Developmental pathways
• others?
Analogy
• Different structures which perform the same
function (Owen, 1843)
• Convergence: Similarities between organisms
that evolved independently.
Tasmanian wolf
Mexican wolf
Foquieria –
Foquieriaceae
North America
Allauidia –
Didieriaceae
Madagascar
Counterarguments
• “Convergent evolution is used by
evolutionists to explain homologies that do
not line up with the evolutionary tree.”
• The probability of a beneficial mutation is
very low. In addition, the probability of two
different organisms with the same
configuration from the same mutation is
astronomically low.
Convergence = directionality?
• Oakley and Cunningham 2002
-“When you examine the tapestry of evolution you
see the same patterns emerging over and over
again. Gould's idea of rerunning the tape of life
is not hypothetical; it's happening all around us.
And the result is well known to biologists —
evolutionary convergence. When convergence
is the rule, you can rerun the tape of life as often
as you like and the outcome will be much the
same. Convergence means that life is not only
predictable at a basic level; it also has a
direction.” (Simon Conway Morris 2002)
Design or Mere Accident?
• “The mechanism of Darwinism is at last securely
founded” and as a consequence “man has to understand
that he is a mere accident.” - Jaques Monod, 1970
• Two questions:
Design or Mere Accident?
• “The mechanism of Darwinism is at last securely
founded” and as a consequence “man has to understand
that he is a mere accident.” - Jaques Monod, 1970
• Two questions:
1. Why does a naturalistic mechanism preclude a divine
scheme?
2. Are just men an accident, or are women merely
accidental as well?
What is the PURPOSE of this
seminar??
What is the PURPOSE of this
seminar??
• Understand evidence for evolution
• Allow scientists in different fields the
opportunity to discuss their perspectives
• Circle the wagons against ID
• Critically discuss how we can best
communicate “evolution” to a nontechnical audience
What is the PURPOSE of this
seminar??
• Awareness of the limits of science: the full
range of the human experience cannot be
explain by science alone
• Openness to questioning and inquiry, and
accepting the possibility of being wrong.
• Reverence for life: life is amazing, should
we not all be in awe of biodiversity?
Evolution vs. ID: Does it matter?
If so, why?
• How do we stop the current loss of
biodiversity?
• Is this debate sucking energy away from
the crisis at hand?
• Can we find common ground and work
together toward protecting the planet?