Tuesday, October 27 2009
• Pre-test
• Discussion of writing assignment & student
questions
• Video
• Activity on the reading
Biological evolution: Overview
•
•
•
•
•
Darwin and his theory
Diversity of life
Mendel and genetics
Human evolution
Societal implications
Image from Wikipedia
Author: Jose Braga
Source :National Human Genome Research Institution
Source: Stefan Laube
Source: Derek Ramsey
Emerald boa, one of many tropical snakes.
A tree sloth, who spends most of each
day hanging as you see here.
Image from US Fish & Wildlife Service
Jaguar
Source: Richard Bartz
A colorful butterfly.
Why is it important to understand evolutionary
theory?
• It changed the way humans viewed their place in the
universe (philosophical)
• It is an rich example of the changing nature of
scientific knowledge
• It has enormous predictive power and is supported by
an large body of evidence (it is consistent with data)
• It is the force that explains the diversity of life on
earth, allowing us to make sense of the biological
world
• It has major implications for human welfare
(microbial resistance)
Writing assignment on podcast
• What were the main points that Elliott Sober
made about the development of Darwin’s
idea?
• What was surprising to you?
• What questions did you have about evolution?
Student questions
• Fell into roughly four main categories:
– Questions about the science
– Questions about the cultural context
– Questions about human evolution
– Questions about science and religion
Student questions
• In groups, identify 2-3 questions on the list
that are interesting to your group
• Be prepared to share:
– Why you found the question interesting
– Summary of discussion and possible answers
– What is the nature of the evidence required to
answer the question?
– How you might go about finding out more?
– What are the scientific certainties and
uncertainties?
How do we know evolution
happens?
Video clip from PBS program, Evolution
• http://www.pbs.org/wgbh/evolution/library/11/2/e_s_1.html
Video clip from Evolution: Darwin’s Dangerous Idea
• http://www.pbs.org/wgbh/evolution/library/01/1/l_011_20.html
Scientific theory
Video clip from AMNH on theories
• http://www.amnh.org/exhibitions/darwin/evolution/theory.php
Video clip from PBS’s Evolution, “Is evolution just a
theory?”
• http://www.pbs.org/wgbh/evolution/library/11/2/e_s_1.html
Evolution is a theory that unites
many areas of research:
Classification
Behavior
Morphology
Genetics
Physiology
Biogeography
Paleontology
Evolutionary relationships and the diversity
of life
• How do we classify life on Earth?
• How do we determine the patterns of
relatedness between species?
• What evidence is used to determine these
patterns?
• Where do we see uncertainty in the data?
Common
ancestor of
birds and
dinosaurs
Common
ancestor of
humans and
dinosaurs
Consider four butterflies connected to their
parents
offspring
parents
Population
past
Individuals
future
Population
Phylogeny
Lineage/ Species
What happened here?
Lineage-branching
Speciation
Most speciation (the
production of new
species)
is due to geographical
barriers
Representation of phylogenies
A
B
The True History
C
A
B
A simplified
representation
C
When reading a phylogeny:
1) It is tree-like, not ladder like
2) There is no “advancement”
3) For any speciation event on a
phylogeny, the choice of which
lineage goes left and which goes
right is arbitrary:
Humans didn’t evolve from chimps, they share a
common ancestor that was neither chimp nor
human
Relatedness = How recent is the common
ancestry
• You are more closely related to your first cousins
than to your second cousins because you share a
more recent common ancestor
– grandparents vs. great-grandparents
• You are more closely related to a chimpanzee than to
a worm because you share a more recent common
ancestor
≈ 6 Million years ago vs. ≈ 600 Mill. years ago
Fish
Newt
Lizard
Mouse
Human
Is a newt more closely related to a fish
or a human?
Why might you go wrong?
If you look “along” the top
Fish
Newt
Lizard
Mouse
Human
Is a newt more closely related to a fish
or a human?
Fish
Newt
Lizard
Mouse
Human
• But this is not how evolution happened
• All these species are alive today: A living fish is not
an ancestor of a newt
• The order “along the top” can change without
changing the content of the tree
Which of the following is different?
A
A
B
E
D
D
E
C
B
C
D
E
C
A
B
D
E
C
A
B
Why are phylogenies useful?
• They provide the basis for biological classification
• They allow us to infer the evolutionary history of
traits (when, where, and why they evolved)
How can we use a tree to make inferences
about character evolution?
Suggests one change
from yellow to red
Parsimony: pick the mapping that involves fewest changes
By parsimony, where did flower color
change?
D
B
E
C
A
Sometimes more than one
change must have taken place
Suggests that red-flower in the two groups are not
really the “same” or homologous