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.