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Evolution:Change in population characteristics over generations

OUTLINEEvolution and common descent

History of evolutionary thought

Evidence for evolution

Evaluating models

Evolutionary novelty

Goals: Be able to…Explain the central tenets of evolution.

Explain how natural selection leads to evolution.

Describe how Darwin came up with the theory of common descent.

Central tenets of evolution

1. Populations have changed over time into the different species we see today

2. Theory of Common Descent: These populations changed from a common ancestor

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Fig 9.2

Natural selection is a mechanism of evolution

Microevolution: Change over short periods

Mixed lice Resistant lice survive

Resistant lice

Apply permethrin

Fig 9.1

Fig 9.2

Natural selection

Speciation: formation of new species

OUTLINEEvolution and common descent

History of evolutionary thought

Evidence for evolution

Evaluating models

Evolutionary novelty

Historical ideas about evolution:Separate (“special”) creation:

Species are fixed on a scale of complexity with humans on top.

The world is perfect.

-- Plato, Aristotle …

Fig 9.7

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Theory of Common Descent

1. Views of Lamarck (evolutionist)

2. Views of Lyell (geologist)

3. Fossil evidence

4. Travels to Galapagos

Lamarck:Organisms change over generations

Due to the Biblical flood?

Result: Earth is much > 10,000 yo

Or, due to gradual changes over very long time periods?

Lyell

Fossils of dinosaurs: some species don’t make it

Result: The world is not perfect

5 year expedition around the world

Fig 9.4

Galapagos giant tortoises

Different kinds of giant tortoises on different islandsResult: Giant tortoises must be related, but diverged over time

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Fig 9.2

Giant

Darwin published “On the Origin of Species by Means of Natural Selection” in 1859

Alfred Russell Wallace Darwin

True/False: Fossils of species that don’t exist today, in combination with a lack of fossils of modern species, support the idea that organisms have NOT evolved over time.

1. True2. False

OUTLINEEvolution and common descent

History of evolutionary thought

Evidence for evolution

Evaluating models

Evolutionary novelty

Goals: Be able to…Describe how classification, homology, biogeography, and fossils all provide evidence for the theory of common descent.

Differentiate between analogy and homology.

Apply your knowledge of radiometric dating to problems.

Discuss evidence refuting various alternative hypotheses of evolution.

Describe 3 ways in which evolutionary noveltycan be generated by small changes.

Do you agree or disagree with the statement: “Human beings, as we know them, developed from earlier species of animals.”1. Agree2. Disagree3. Don’t know

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“Human beings, as we know them, developed from earlier species of animals.”

Agree Disagree

Hypothesis 1: Static model

Fig 9.7

Fig 9.7

Hypothesis 2: Transformation

Fig 9.7

Hypothesis 3: Separate types

Independent origins

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Hypothesis 4: Common descent

Fig 9.7

Common origin of life

Scientists investigate evolution, because

1. It is the only acceptable scientific explanation for the observed patterns of change in organisms over time.

2. They are not spiritual or religious people.3. They want to disprove the existence of (a)

Creator(s).4. All of the above.

Evidence for Evolution1. Biological classification

2. Homology of features

3. Biogeography

4. Fossils!

Fig 9.9

Classification suggests relatedness

Why are we able to put organisms into groups?

Fig 9.11

Ancestry represented using trees

More closely related = more recent common ancestor

Evidence for Evolution1. Biological classification

2. Homology of features

3. Biogeography

4. Fossils!

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Homology: Similarity of features due to common ancestry

Fig 9.12Homology

Vestigial structures: evolutionary baggage

Fig 9.13

Vestigial structures Similar genetic sequences

Fig 9.17

True/False: A fish fin and a whale flipper are homologous structures.

1. True2. False

Evidence for Evolution1. Biological classification

2. Homology of features

3. Biogeography: Geographic distributions

4. Fossils!

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Marsupials: Young develop in pouches

PlacentalsMarsupials

Porpoise: mammal

Icthyosaur: reptile

Analogy: similarity due to common function

Convergent evolution: similar features arise due to common environmental pressure, not ancestry.

Evidence for Evolution1. Biological classification

2. Homology of features

3. Biogeography

4. Fossils!

Archaeopteryx: transitional bird-lizard

Transitions in the fossil record

Transitions in the fossil record

Fig 9.28

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Fig 9.21

Fossilization: minerals replace organic matter

How do we know how old fossils are?

Radioactive elements “decay” at a predictable rate.

Decay causes parent elements to turn into daughter elements

Uranium Lead

Half-life is the time it takes for ½ of the parts to decay

Age of the Earth

200 years ago 150 years ago 100 years ago 50 years ago

What is the half-life of this element?

Age of the Earth Age of the Earth

Fig 9.24

1 half-life = 1 million yr

19% left = 2.5 half-lives

100% left

50% left

25% left

12.5% left

Zircon4.5 billion yrsUranium/Lead

Micas47 billion yrsRubidium/Strontium

Volcanic rock1.3 billion yrsPotassium/

Argon

Shells, Limestone, organics

5,730 yrsCarbon/Nitrogen

Materials datedHalf-livesMethod

Age of the Earth If an element has a half-life of 20 million years, and there is 25% of it remaining in a rock, how old is the rock?1. 5 million years2. 10 million years3. 20 million years4. 40 million years

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Group Problem: M&Mite decay

M&Mite spontaneously decays into the daughter product “beanus” over time

1. Using your samples (baggies), graph # of M&Mite molecules vs. Number of half-lives.

2. If your oldest sample is 1000 years old, what is the half-life of M&Mite?

OUTLINEEvolution and common descent

History of evolutionary thought

Evidence for evolution

Evaluating models

Evolutionary novelty

Hypothesis 1: Static model

Fig 9.7

What evidence refutes this theory?

Fig 9.7

Hypothesis 2: Transformation

What evidence refutes this theory?

Fig 9.7

Hypothesis 3: Separate types

Independent origins

What evidence refutes this theory?

Hypothesis 4: Common descent

Fig 9.7

Common origin of life

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We can reject the static hypothesis, because1. We usually do not find fossils record that are

exactly the same as living organisms.2. Fossil evidence indicates that many organisms

have gone extinct.3. Many diverse features share a basic structure

(bat wing & whale flipper bones).4. We can find fossils transitional between

different organisms that are currently alive.5. All of the above.

Example short answer:

List 2 pieces of evidence that refute the static hypothesis. For each piece, state which aspect of the status hypothesis is refuted.

OUTLINEEvolution and common descent

History of evolutionary thought

Evidence for evolution

Evaluating models

Evolutionary novelty

Generation of evolutionary novelty• Exaptation

• Developmental mutations

• Intermediate forms

Exaptations: Features originally performed a different function than they currently do.

Mutations in developmental genes…

Amphistoma larva

Axolotl adult

Have widespread effects

Pigment cells

EyecupPinhole eye

Primitive lens

Complex camera eye

Intermediate forms

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True/False: Both bird feathers and the human eye are irreducibly complex

1. True2. False

Example short answer:

In 1-2 sentences, describe how feathers on birds may have evolved.

Group Problem: Birds on Islands

AB

C

A = Red feathers, blue beaks

B = Red feathers, black beaks

C = Yellow feathers, blue beaks

1. Draw 2 possible phylogenetic trees for these 3 species.

2. What specific evidence would help you choose between these 2 hypotheses?

Goals: Be able to…Describe features that 1) we share with other primates, 2) differentiate apes from other primates, and 3) differentiate us from apes.

Describe the environment in which primate features evolved.

Explain why Lucy was such an important find.

Discuss hypotheses about the origins of bipedalism and big brains.

Tell me when modern humans arose, and about their Homo ancestors.

Primates• Grasping hands

• Forward-facing eyes

• Large brains

Why? Adaptation for forest life

Prosimians: Lemurs and tarsiers

Earliest divergingMonkeys and apes

Opposable thumb!

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Apes• No tail

• Long forelimbs

• Larger brainsFig 9.11

GorillasOrangutans

Bonobos

Chimpanzees

What human features were probably adaptations for forest life?

1. Fingernails2. Forward-facing eyes3. Opposable thumbs4. Lack of hair5. 2 and 36. All of the above

Example short answer:

List 2 human features that were originally adaptations for forest life.

-OR-

Give 2 ways in which apes are distinct from other primates.

What does it mean to be human?1) Large brain 2) Bipedalism 3) Short jaw

4) Reduced sexual differences 5) Monogamy

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Fig 9.22

Comparing humans vs. chimps

Hominins: Most closely related to us.

Diverged from chimpanzee line: 5-7 mya?

Fig 9.25

What features separate humans from other apes?

1. Forward-facing eyes2. Opposable thumbs3. Long arms4. Largest brain

Example short answer:

What are the most critical 2 ways in which human anatomy differs from other apes?

Enlarging brain

Fig 9.27

Looking for 2 major features:

• Bipedal posture

• Enlarged brain

How did they evolve?Early ideas:

Brain sizeBipedal posture

+

+

Dry savanna provides more complexity?

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Along came Lucy…

~ 3.5 mya: Australopithecus afarensisFig 9.23 Australopithecus afarensis

Homo sapiens

Fig 9.23

Problem: Bipedal with small brain

Early theories:

Brain sizeBipedal posture

+

+

Bipedal posture is the key!!!

Why bipedalism?

Why might bipedalism be favorable in a savanna (as opposed to forest) environment?

Environmental change dry savannas

Why bipedalism?

Not using hands for tree climbing?

Easier to see far away?

Easier to carry things?

Prevent overheating?

Environmental change dry savannasBipedalism paved the way for large brain?

Babies born smaller due to pelvis…

Longer care of infants more culture?

Hands free to create tools…?

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True/False: Looking at human evolution, we can see that bipedalism developed before large brain size.1. True2. False

Example short answer:

What did the fossil Lucy demonstrate about the order of evolution of bipedalism and big brains?

Fig 9.25

Genus: Homo

Homo habilis: “handy-man”

First tool-maker

Brain size: 47% of ours

Homo erectus

Specialized tools

Brain size: 71%

Homo erectus colonized Asia and Europe

Neanderthals: 500,000 – 30,000 years ago?

Homo sapiens neanderthalensis

Brain size: 12% larger

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Homo sapiens sapiens: 100,000 years ago. Origins of agriculture begin 9500 BC

Cultural evolution…

Homo floresiensus: The HobbitAlive 13,000 years ago

What do you think about the statement:

“God created man pretty much in his present form at one time within the last 10,000 years.”

Example short answer:

What scientific support is there that humans share a common ancestor with chimpanzees?