darwin’s theory of evolution. historical context (early 1800s) aristotle, judeo-christian culture,...
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Darwin’s Theory of Evolution
Historical Context (early 1800s)
• Aristotle, Judeo-Christian culture, book of Genesis…–The earth is only 6000 years old–All living species are “static” (put
here ‘as is’)
Pre-Darwin
• Lamarck (early 1800s)• Buffon
• Inheritance of AcquiredCharacteristics
Inheritance of Acquired Characteristics
• Why do giraffes have long necks?
Because they stretch them during their lifetime, then
their offspring have longnecks
The theory of “Use & Disuse”
Who was Darwin?
• Surgeon in training• Minister• Recruited by captain of HMS
Beagle• Set sail in 1831 at the age of 22
Not just the Galapagos…
Not just finches…
Darwin made 3 main observations…
• 1. Members of a population vary in their physical traits.
• 2. Many physical traits are inherited from parent to offspring.
• 3. All species are capable of reproducing more offspring than the environment can support.
And drew 2 conclusions:
• 1. Individuals who inherit traits that give them a better chance of surviving tend to leave more offspring than other individuals
• 2. This unequal reproduction of offspring causes ‘favorable’ traits to accumulate in a population over generations.
(“survival of the fittest; struggle for existence)
• Darwin called these conclusions “Descent with Modification”
• We call it “Natural Selection”
Important!!
• What is ‘favorable’ in one environment may not be in another environment.
• The environment determines what is favorable and unfavorable.
4 Take-home Points about Natural Selection
• 1. Individuals DO NOT evolve. Evolution refers to generation-to-generation changes in a population.
• 2. Natural selection can only amplify or diminish traits that are inheritable.
4 Take-home Points about Natural Selection
• 3. Evolution is NOT goal-directed. No notion of “perfect species.”Environmental factors vary in place & time…’favorable’ traits will also vary.
4 Take-home Points about Natural Selection
• 4. Evolution is about compromise.
It’s all about timing…
• Darwin formulated his idea of natural selection in the early 1840s.
• He did not publish them until 1858.
Conflict!
Alfred Wallace
What Data did Darwin collect?(i.e., what is the evidence for
evolution?)
• 1. Fossil Record• 2. Biogeography• 3. Comparative Embryology• 4. Comparative Anatomy• 5. Molecular Biology
A Skull of Homo erectusB Ammonite casts C Dinosaur tracks
Fossilized organicmatter of a leaf E Insect in amber
F “Ice Man”
D
1. The Fossil Record
Pelvis andhind limb
Rhodocetus (predominantly aquatic)
Pakicetus (terrestrial)
Dorudon (fully aquatic)
Balaena (recent whale ancestor)
Pelvis andhind limb
NorthAmerica
= Living lungfishes
Australia
Africa
AsiaEurope
SouthAmerica
= Fossilized lungfishes
2. Biogeography
Present
Eurasia
Mill
ion
s o
f ye
ars
ago
65.5
135
251
Mes
ozo
icC
eno
zoic
Pa
leo
zoic
Madagascar
India
Australia
Africa
Antarctica
SouthAmerica
North Americ
a
Laurasia
Gondwana
Pangaea
2. Biogeography
All the species of finches on the Galapagos Islands look like finches native to the West Coast of South America—but not exactly the same
“Adaptive Radiation”
Pharyngealpouches
Post-analtail
Chick embryo Human embryo
3. Comparative Embryology
Humerus
Radius
Ulna
Carpals
MetacarpalsPhalanges
Human Cat Whale Bat
4. Comparative AnatomyHomologous Structures = Divergent Evolution
Pelvis andhind limb
Dorudon (fully aquatic)
Balaena (recent whale ancestor)
Pelvis andhind limb
4. Comparative Anatomy
Vestigial Structures: What are left of homologous structures
Dorudon
Balaena
Modern-Day Humpback Whale
Analogous Structures = Convergent Evolution
Ho
mo
log
ou
sA
nalo
go
us
5. Molecular Biology
http://www.geneticorigins.org/mito/media2.html
http://evolution.berkeley.edu/evosite/evo101/IIE1cMolecularclocks.shtml
Comparison of DNA sequences from different organisms is very helpful in determining relationships.
Molecular analysis is best done together with other types of analyses.