darwin’s theory of evolution1

8/2/2019 darwins theory of evolution1

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Mexican Tetra Sighted


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Basic premises for this discussion

Evolution is not a belief system. It is ascientific concept. It has no role in defining

religion or religious beliefs

Evolution is a theorybut you dont getany better than that in science

There is a lot of contention aboutevolution, but not among scientists orscientific organizations.


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Some basic definitions

Theory: a well-substantiated

explanation that incorporates facts,

laws, inferences and tested hypotheses.

In science, you dont get anybetter than a theory.


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Darwins Theory of Evolution


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Pre-Darwin

Lamarck (early 1800s)

Inheritance of Acquired

Characteristics


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Inheritance of Acquired Characteristics

Why do giraffes have long

necks?

Because they stretch them

during their lifetime, then

their offspring have longnecks

The theory ofUse & Disuse


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Who was Darwin?

Surgeon in training

Minister

Recruited by captain of HMS

Beagle

Set sail in 1831 at the age of 22


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Not just the Galapagos


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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.


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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)


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Darwin called these

conclusions Descent with

Modification

We call it Natural Selection


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Important!!

What is favorable in one

environment may not be in another

environment.

The environment determines what isfavorable and unfavorable.


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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 areinheritable.


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Selection

3. Evolution is NOT goal-directed.

No notion ofperfect species.

Environmental factors vary in place &timefavorable traits will also vary.


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Selection

4. Evolution is about compromise.


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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


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GO TO EVIDENCE POWER POINT


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A Skull of Homo erectusB Ammonite casts C Dinosaur tracks

Fossilized organicmatter of a leaf E Insect in amber

FIce Man

D

1. The Fossil Record


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Pelvis andhind limb

Rhodocetus(predominantly aquatic)

Pakicetus(terrestrial)

Dorudon(fully aquatic)

Balaena(recent whale ancestor)

Pelvis andhind limb


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2. Biogeography

All the species of

finches on the

Galapagos Islands

look like finchesnative to the West

Coast of South

Americabut not

exactly the same

Adaptive

Radiation


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Pharyngealpouches

Post-analtail

Chick embryo Human embryo

3. Comparative Embryology


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Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human Cat Whale Bat

4. Comparative AnatomyHomologous Structures = Divergent Evolution


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Pelvis andhind limb

Dorudon(fully aquatic)

Balaena(recent whale ancestor)

Pelvis and

hind limb

4. Comparative Anatomy

Vestigial Structures: What are left of

homologous structures


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Dorudon

Balaena


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Modern-Day Humpback Whale


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Analogous Structures = Convergent Evolution

H

omologous

An

alogous

darwin’s theory of evolution1

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