Fossils of extinct animals show how they may have evolved from preexisting species.

• Front Leg

• Hind Leg

Pterodactyl

Bird

Bat

Dolphin

metacarpals

Seal

Dog

Sheep

Shrew

humerus

radius

ulna

carpals

phalanges

Human

Structures in many animals develop from the same tissues, just are different shapes.

Some structures in animals no longer serve a purpose, but are thought to have been passed down from their ancestors.

Homologous structures are structures that develop from the same tissues in different species but have different adaptations.

• compare common genes
• compare common proteins

number of amino acids different from human hemoglobin

You would expect to find similar DNA sequences in species that share a more recent common ancestor.

Evolution:

Just a Theory?

If species have not changed, then what evidence would support that?

1. Species that lived in the remote past (lower layers) should be similar to those living today.
2. The older layers should be just as likely to contain fossils similar to present-day species as the younger layers.
3. The simplest as well as the most complex organisms should be found in the oldest layers containing fossils, as well as in more recent layers.
4. Comparison of fossils from layer to layer should not show gradual changes in fossil forms, in other words, intermediate forms should not be found.

Compare the bones

• The same bones under the skin
• limbs that perform different functions are built from the same bones

Evidence supporting evolution

• Fossil record
• shows change over time
• Anatomical record
• comparing body structures
• homology & vestigial structures
• embryology & development
• Molecular record
• comparing protein & DNA sequences
• Artificial selection
• human caused evolution

1. Fossil record

• Layers of rock contain fossils
• new layers cover older ones
• creates a record over time
• fossils show a series of organisms have lived on Earth
• over a long period of time

Fossils tell a story…

the Earth is old

Life is old

Life on Earth has changed

Evolution of birds

Fossil of Archaeopteryx

• lived about 150 mya
• links reptiles & birds

Today’s organisms descended from ancestral species

Land Mammal

Where are the�intermediate fossils?

Ocean Mammal

Someone’s idea of a joke!

But the joke’s on them!!

We found the fossil — no joke!

Evolution from sea to land

• 2006 fossil discovery of early tetrapod
• 4 limbs
• Missing link from sea to land animals

How do fossils form?

1. Organism becomes compressed by overlying sediment.
2. As organism decays, this leaves a mold in surrounding rock.
3. Mold is then filled with other sediment forming a cast.
• Can be internal or external

Unaltered Fossils

Real Bone

Teeth

Amber

Mummification

Altered Fossils

Carbonization

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Cast

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Mold

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Petrification

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The fossil record – different forms of life

Ediacara

Burgess Shale

Dickensonia

~ 550 MY

Marella

~ 500 MY

Burgess shale

First fossils:

• Resemble modern day bacteria
• Date as early as 3.7 billion years ago

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Fossil Evidence

• If species change why don’t we see that in the record?

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• Transitional Fossils

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Transitional Fossils

What is a transitional fossil?

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Why are transitional fossils important in understanding evolution?

Transitional Fossils

What is a transitional fossil?

A: Those fossils with a mixture of the features of two, but related, taxonomic groups

Why are transitional fossils important in understanding evolution?

A: they show that one group may have given rise to the other by evolution (descent with modification)

Horse Transitions

• Front Leg

• Hind Leg

Pakicetidae: The First Whales

Pakicetidae: The First Whales

The skulls of two pakicetid whales flank the skull of a modern coyote ( Ichthyolestes on the left, Pakicetus on the right).

Ambulocetidae:�The First Costal Whales

Ambulocetidae:�The First Costal Whales

• Although ambulocetids

could walk on land as

well as swim, it is clear

that they were not fast on either terrain.

• The name of this whale means “the walking and swimming whale,” and indicates that it was amphibious.

Remingtonocetidae �Whales Endemic to the Indian Subcontinent

• Their heads were very different from other whales.
• Their eyes were small, their snout long, and they had ears that transmitted sound similarly to those of modern whales.
• Remingtonocetids had long fore- and hind limbs.

Dorudontids

• Dorudontids had complete hindlimbs, that included a mobile knee and several toes.
• However these extremities were tiny, so small that they were certainly not important in aquatic propulsion.

Odontocetes

Mysticetes�

Whale evolution

1. Why does the whale fossil record provide a good example of evolution?
2. Briefly describe the adaptations of whales for swimming that evolved over time?

Whale evolution

• Why does the whale fossil record provide a good example of evolution?

A: Shows many transitional forms with the accumulation of adaptations for ocean life over time. Early forms have more terrestrial features, later forms more features for the ocean. Evolved from life on land to life in the ocean.

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Whale evolution

2. Briefly describe the adaptations of whales for swimming that evolved over time?

A: Streamlined shape, broad tail, forelimbs are flippers, vestigial hind limbs, nostrils modified as a blowhole.

Dating Techniques

Relative Dating: age of fossil by stating whether it is younger or older than another fossil or event.

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Absolute Dating: a specific age for the fossil is made by measuring the amount of decay in the fossil.

Absolute Dating

• Unstable so decay over known periods of time.

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• By determining how much has decayed we see old it is.

Absolute Dating

• One Half Life = 50% of the isotope has decayed

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• Half Life differs for each isotope.

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• Two Half Lives = 25% remains (75% decayed).

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• Three Half Lives = 12.5% remains (87.5% decayed).

Radiometric Dating (%)

• Carbon 14 = 5730 years

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• 6% Carbon 14 remains, how old?

50 % 1 HL

25 % 2 HL

12.5 % 3 HL

6.25 % 4 HL

~4 HL x 5,730 yr =

~22,920 yr

3. Anatomical record

Animals with different structures on the surface

But when you look under the skin…

It tells an evolutionary story of common ancestors

Compare the bones

• The same bones under the skin
• limbs that perform different functions are built from the same bones

Homologous structures

• Structures that come from the same origin
• homo- = same
• -logous = information
• Forelimbs of human, cats, whales, & bats
• same structure
• on the inside
• same development in embryo
• different functions
• on the outside
• evidence of common ancestor

But don’t be fooled by these…

• Analogous structures
• look similar
• on the outside
• same function
• different structure & development
• on the inside
• different origin
• no evolutionary relationship

Solving a similar problem with a similar solution

How is a bird�like a bug?

Pterodactyl

Bird

Bat

Dolphin

metacarpals

Seal

Dog

Sheep

Shrew

humerus

radius

ulna

carpals

phalanges

Human

Evidence of evolution

• Vestigial structures
• Structures serve no apparent purpose but are homologous to structures in related organisms

• Nature’s imperfections
• Ear-wiggling
• Vital to survival, or good party trick?

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Vestigial structures

• Analogous organs: organs that have similar look and/or functions in different organisms, but do not share a common embryonic origin.
• For example:
• Wings of insects vs. wings of birds

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Analogous Structures

Wings

Analogous structures

• Dolphins: aquatic mammal
• Fish: aquatic vertebrate
• both adapted to �life in the sea
• not closely related

Watch the tail!

Convergent evolution

• 3 groups with wings
• Does this mean they have a �recent common ancestor?

Flight evolved 3 separate times —

evolving similar solutions to similar “problems”

NO!

They just�came up �with the �same answer!

Convergent evolution led to mimicry

• Why do these pairs look so similar?

Monarch male

poisonous

Viceroy male

edible

fly

bee

moth

bee

Which is the fly vs. the bee?

Which is the moth vs. the bee?

Vestigial organs

• Hind leg bones on whale fossils

Why would whales have pelvis & leg bones if they were always sea creatures?

Because they �used to �walk on land!

Comparative embryology

• Development of embryo tells an evolutionary story
• similar structures during development

Forelimb adaptations

Bats, Dogs, Humans, and Whales

Anatomical Evidence for Evolution

1. What is a pentadactyl limb?
2. Explain how homology in the pentadactyl limb provides evidence for adaptive radiation?

Anatomical Evidence for Evolution

• What is a pentadactyl limb?

A: a limb with 5 fingers or toes

• Explain how homology in the pentadactyl limb provides evidence for adaptive radiation?

A: limbs all share the same basic bone anatomy, although highly modified in some cases. Bones can be matched, but also recognize how bones have changed to better perform a new function in a new niche.

3. Molecular record

• Comparing DNA & protein structure
• everyone uses the same genetic code!
• DNA

• compare common genes
• compare common proteins

number of amino acids different from human hemoglobin

Building “family” trees

Closely related species are branches on the tree — coming from a common ancestor

4. Artificial selection

• How do we know natural selection can change a population?
• we can recreate a similar process
• “evolution by human selection”

“descendants” of wild mustard

Selective Breeding

Humans create the change over time

“descendants” of the wolf

Artificial Selection

…and the examples keep coming!

I liked �breeding �pigeons!

Artificial Selection gone bad!

• Unexpected consequences of artificial selection

Pesticide resistance

Antibiotic resistance

Insecticide resistance �

• Spray the field, but…
• insecticide didn’t �kill all individuals
• variation
• resistant survivors reproduce
• resistance is inherited
• insecticide becomes less & less effective

Teosinte (left) and its modern descendent, corn, a product of artificial selection

Parallel Evolution

filling similar roles in nature, so have similar adaptations

not closely related

Vestigial organs

• Structures on modern animals that have no function
• remains of structures that were functional in ancestors
• evidence of change over time
• some snakes & whales have pelvis bones & leg bones of walking ancestors
• eyes on blind �cave fish
• human tail bone

Radiometric Dating

• Use multiple samples sent to multiple labs

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• All results have to be similar.

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• Take into account other fossils & position.

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• Take into account what is already known.

Fossils – continuity of form

Homo erectus

1.8 MY

Homo sapiens (early form)

0.18 MY

Homo sapiens (modern)

0.01 MY

Evidence of evolution

• Comparative anatomy
• Comparing the bodies of organisms to look for similarities and differences
• Homologous structures
• Structures in the anatomy with the same embryonic origin, but may have different functions
• Lettuce leaves, vine tendrils, cactus spines – have different functions, but same origin (leaf)

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Evidence of evolution

• Comparative embryology
• All vertebrate embryos look similar to one another in early development, with the development of a tail and gill slits

Pharyngeal slits, color-coded here, exist in the embryos of these five vertebrate animals: (a) sea lamprey, (b) pond turtle, (c) chicken, (d) domestic cat, and (e) human being. The common structure is evidence that all five evolved from a common ancestor. (Adapted from M. K. Richardson, 1997.) Krogh, Biology: A Guide to the Natural World 2^nd ed.

Evidence of Evolution

Embryonic history

• Ernst Haeckel mid- 1800’s
• Ontogeny recapitulates phylogeny
• Many ideas were discredited.
• Similarity of embryonic features still provides evidence of common ancestry

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Developmental Biology

• Early embryos of different mammal species look very much alike – they share common features (gills, tail, etc.).