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Chapter 21:

Evidence for Evolution

I. Evolution & Darwin

II. Artificial Selection

III. Fossil Record

IV. Comparative Anatomy

V. Embryology

VI. Genetic Analysis

VII. Biogeographical Evidence

VIII. Conclusions

“Nothing in biology makes sense except in the light of evolution”

--Theodosius Dobzhansky

Evolution = descent with modification

! Macroevolution = large changes

! Microevolution = small changes

I. Evolution & Darwin

Charles Darwin:

On the Origin of Species

(mid-1800’s)

• Traveled extensively

• Galapagos Islands

– off the coast of Ecuador

• One area of focus: finches

Both rely on same mechanisms!

Primarily natural selection

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• Finches of the Galapagos

• 14 species

• Difference between them:

– Beak shape

• Seed crackers

• Cactus eaters

• “Tool users”

• Vampire

I. Evolution & Darwin

• Darwin’s idea:

– One original species has adapted to different food

sources

II. Artificial Selection

CAN selection produce major evolutionary change?

! Darwin found convincing evidence for his ideas in the results of

artificial selection

Artificial selection:

• organisms may be modified by controlled breeding

• and change drastically in short time periods!

• 3 examples…

A) Plants

!Broccoli, brussel sprouts, kale,

cabbage, & cauliflower

! All artificially selected

from Brassica oleracea

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B) Insects: Pesticide resistance

(Florida)

Agent of Natural Selection:

Pesticide called "Combat®"

– Cockroaches who like

bait: continuously killed

– Those who didn’t like

bait: survived

• Had rare, glucose

disliking mutation

– Bait now is ineffective>>

populations are resistant

II. Artificial Selection (cont.)

C) Mammals: Dogs

II. Artificial Selection (cont.)

Change can happened

over a very short

geological period if the

selection pressure is

strong!

READ 420-421

SILVER FOX

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Fossils: Preserved remains of ancient organisms

III. The Fossil Record

How to make a fossil:

! Burial in sediment

! Mineralization of organic

material

! Hardening of sediment

III. The Fossil Record

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Darwin and his contemporaries saw and knew of fossils:

! Local fossils looked like local organisms

! Progressive changes in layers

• Fossil Record

– Remains or evidence of past life

– Dating fossils

• Relative dating – old layers under new

• Absolute dating – radioactive decay

– Fossilization chancy

• Right kind of organism, in right place

• Gaps unavoidable

– Many excellent series though

• Horses, titanotheres, whales, humans

III. The Fossil Record

Organization of fossils:

a) Fossils are found in distinct layers

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b) Resemblance to modern forms oflife gradually increases withyounger fossils

c) Many fossils are of species nowextinct

Conclusions:

! Many different types of organismsin the past (some extinct)

! Change in lineages over time

Organization of fossils:

a) Fossils are found in distinct layers

Facts – Geology and Fossils

• Fossils are found in sedimentary rocks

• Many fossils represent extinct organisms

• Oldest sedimentary rocks contain no fossils, or fossils of

extremely simple organisms

– Prokaryotes (stromatolites)

• Fossil prokaryotes appear prior to fossil eukaryotes

• Colonial eukaryotes appear prior to multicellular

eukaryotes (invertebrates and plants)

• Invertebrates appear prior to vertebrates–Fish, amphibians, reptiles, mammals, and birds appear in order

• Seedless vascular plants, seeds, gymnosperms, and

angiosperms appear in order

III. The Fossil Record

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Unstable isotopes decay at a constant and predictable rate

Allows setting of absolute age on rock strata.

One conclusion: the Earth is very old ! ~4.5 billion years

READ 422

Fossil recordevidence ofevolutionarychange over time

Ancient primitiveorganisms !

Several intermediarystages

!Modern forms

How Do We Know That Evolution Has Occurred?

READ 423-425

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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Modern toothed whales

Ambulocetus natans

walked on land …like sea lions

swam by flexing & paddling … like otters

Pakicetus attocki

lived on land;skull had whale characteristics

Rodhocetus kasrani

reduced hind limbscould not walk;swam with up-down motionlike modern whales

Whale Evolution:

Fossil Record of Evolution

READ 422-423

Cambrian

(545-490)

Ordovician

(490-438)

Silurian

(438-408)

Devonian

(408-360)

Carboniferous

(360-280)

Permian

(280-248)

Triassic

(248-213)

Jurassic

(213-144)

Cretaceous

(144-65)

Tertiary

(65-2)

Millions of years ago

800

600

400

200

0600 500 400 300 200 100 0

Nu

mb

er

of

fam

ilie

s

Diversity over the Last 600 Million Years

III. The Fossil Record: Evidence for Mass Extinctions

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IV. Comparative Anatomy

• Organisms can be grouped (classified) by

unique anatomical characteristics

• Similar anatomy is found in organisms with

greatly divergent functions

Homologous structures

! structures that may have different appearances andfunctions, yet all derived from a common ancestor

Similar anatomy is found in organisms with

greatly divergent functions

Evolution helps us understand patterns in the diversity of life

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Vestigial structures

! No apparent purpose

! Resemble similarfunctional structures inother, closely relatedspecies

! also human appendix

Vestigial structures are Evolutionary relicts. They

present a strong argument for common ancestry.

V. Embryology and Comparative Development

Embryological stages

!All vertebrate embryos look

similar early in their

development

!evidence of common ancestry

! similar developmental

“instructions” in DNA

pig cow rabbit human

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Comparative Development Reveals

Descent from a Common Ancestor

V. Embryology and Comparative Development

VI. Genetic Analysis

• Essentially all organisms have DNA as genetic material

• With very few exceptions, all organisms use the same

genetic code

• Similarities in genes and proteins exist in predictable ways

(based on morphological similarities)

Modern technology reveals relatedness among diverseorganisms

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Molecular Record – Independent test

! Distantly related organisms are expected to accumulate a greater

number of evolutionary differences than closely related species.

VII. Biogeographical Evidence

• Islands often have unique (endemic) species

• Species on islands are most similar to those onnearest continent (or nearest island)

Species of Gallotia lizards on

the Canary Islands

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• Different continents have different species

• Modern species on any continent are most similar to

fossils on that continent

VII. Biogeographical Evidence

Evolution in Action• Darwin’s Finches – beak size

– Grant and Grant – 1970s

• Showed beak size heritable and responsive to

environmental change

• Guppies – with and without predators

• Pesticide and Antibiotic resistance

• Peppered Moths/Industrialized Melanism!

VIII. Conclusions

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VIII. Conclusions READ 416-417

Evolution – Supported by Many

Independent Lines of Evidence

!Evolution requires that all of these facts are trueand congruent with each other.

– Fossils, Order of Appearance, Relative andAbsolute Dates

– Anatomical Classification, Vestigial Structures,Homologies

– Embryology

– Biogeography

– Genetic Analysis

VIII. Conclusions

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Evolution – Both a Fact and a Theory

• That evolution has occurred (and is currently

occurring) is NOT in scientific debate now; it has been

settled.

• FACT – The biodiversity on Earth is a result of

evolution from a common ancestor.

• FACT – Evolution continues today.

• THEORY – The intricacies of evolutionary change and

mechanisms driving evolution.

VIII. Conclusions

Myths

! Evolution is “only a theory”.

– Misuse of word “theory”

– Theory of Gravity, Relativity, Cell theory,

Germ theory of disease etc.

– “Theory” in science means most certain

VIII. Conclusions

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End Evolution