Transcript Darwin\`s Finches

Thursday, October 29 2009
Writing assignment:
http://www.nytimes.com/2009/02/10/science/1
0essa.html?_r=1&scp=1&sq=darwin%20must
%20die&st=cse (Darwinism must die)
And three excerpts from scientists about their
favorite quotes from “Origin of Species”
Then, discuss the beneficial and detrimental
aspects of focusing on Darwin’s work. And,
discuss whether you would have liked him as a
person.
Evolution is a theory that unites
many areas of research:
Classification
Behavior
Morphology
Genetics
Physiology
Biogeography
Paleontology
Scientific theory
Video clip from AMNH on theories
• http://www.amnh.org/exhibitions/darwin/evolution/theory.php
How does evolution work?
• Each organism contains DNA, which carries
the genetic code.
• When DNA replication happens (via RNA),
mistakes can occur in the copying process.
These mistakes or other modifications of the
DNA are mutations.
• Most mutations have no outward effect on
appearance, but some do. Most mutations
are unfavorable for the individual.
How does evolution work?
(continued)
• If the individual with a mutation is able to
reproduce, that mutation may be (but not
necessarily) passed on.
• If the mutation causes an advantage in terms
of survival, even very slight, that mutation
may wind up in greater abundance in the next
generation. This concept is called fitness.
• Thus, while mutations are usually harmful for
an individual, some may be beneficial for a
species.
Fitness
Fitness describes the number of alleles (a
version of a gene) that occur in the next
generation. Fitness includes survival and
reproduction. Inclusive fitness involves the
survival and reproduction of near relatives.
This idea is used because although an
individual might not reproduce, the allele
might survive if siblings do.
How does evolution work?
• While mutations are usually harmful for an
individual, some may be beneficial for a
species. In fact, given the major changes in
the Earth over geological times, mutations are
necessary for survival of life.
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?
Six components of Darwin’s idea
•
•
•
•
•
•
Evolution
Gradualism
Speciation
Common ancestry
Natural selection
Nonselective mechanisms of evolutionary
change
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
Cobert report
Ken Miller
http://www.colbertnation.com/the-colbert-reportvideos/181409/january-12-2006/kenneth-miller
Also
http://www.colbertnation.com/the-colbert-report-videos/173859/june-16-2008/kennethmiller