Ch. 15.2 Evidence of EvolutionCh. 15.3

Objectives:•Describe how fossils provide evidence of evolution•Discuss morphological evidence of evolution•Explain how biochemistry provides evidence of

evolution

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 shape ideas about evolution

Fossils: direct or indirect remains of organisms preserved in media such as sedimentary rock, amber,

ice, or tar

Ammonite casts–Fossilized organic matter in a leaf

–Fossilized organic matter in a leaf Ice Man”

Fossils tell a story…

the Earth is oldthe Earth is old

Life is oldLife is old

Life on Earth has changedLife on Earth has changed

Fossils tell a story…

the Earth is oldthe Earth is old

Life is oldLife is old

Life on Earth has changedLife on Earth has changed

What has the fossil record shown us?• The creatures alive today haven’t

always been around

Different species lived in the pastDifferent species lived in the past

OBSERVATIONOBSERVATION

Land Mammal

?

???

Where are the

intermediate

fossils?

Where are the

intermediate

fossils?

Ocean MammalSomeone’s idea of a joke!

But the joke’s on them!!

Complete seriesof transitionalfossils

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

2. Anatomical record

Animals with different structures on the surfaceAnimals with different structures on the surface

But when you look under the skin…But when you look under the skin…

It tells an evolutionary story of common ancestorsIt 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 solutionSolving a similar problem with a similar solution

How is a birdlike a bug?

Analogous structures Dolphins: aquatic mammal Fish: aquatic vertebrate

both adapted to life in the sea

not closely related

Watch the tail!

Vestigial organs structure—a body structure in a present-day organism that no longer serves its original purpose,

but was probably useful to an ancestor.

• Hind leg bones on whale fossils

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

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

all vertebrate embryos have a “gill pouch” at one stage of development all vertebrate embryos have a “gill pouch” at one stage of development

3. Molecular record

100 20 30 40 50 60 70 80 90 100 110 120

LampreyFrogBirdDogMacaqueHuman

328 45 67 125

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

compare common genes compare common proteins

compare common genes compare common proteins

number of amino acids different from human hemoglobinnumber of amino acids different from human hemoglobin

Building “family” treesClosely related species are branches on the tree — coming from a common ancestorClosely related species are branches on the tree — coming from a common ancestor

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

4. Artificial selection

“descendants” of wild mustard“descendants” of wild mustard

Selective BreedingHumans create the change over timeHumans create the change over time

“descendants” of the wolf“descendants” of the wolf

Artificial Selection gone bad!• Unexpected

consequences of artificial selection

Pesticide resistancePesticide resistance

Antibiotic resistanceAntibiotic 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

Adaptations: Evidence for Evolution

• an adaptation is any variation that aids an organism’s chances of survival in its environment.

• According to Darwin’s theory, adaptations in species develop over many generations

• Learning about adaptations in mole-rats can help you understand how natural selection has affected them.

Structural adaptations arise over time

• camouflage, an adaptation that enables species to blend with their surroundings.

• Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.

Structural adaptations arise over time

• Mimicry is a structural adaptation that enables one species to resemble another species.

• Predators may learn quickly to avoid any organism with their general appearance

Physiological adaptations can develop rapidly

• In general, most structural adaptations develop over millions of years.

• However, there are some adaptations that evolve much more rapidly.• The evolution of insecticide resistance is an example of natural selection in action

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”

Flight evolved 3 separate times — evolving similar solutions to similar “problems”

NO!

They justcame up with the same answer!

Convergent evolution led to mimicry• Why do these pairs look so similar?

Monarch malepoisonous

Viceroy maleedible

fly bee moth bee

Which is the fly vs. the bee?Which is the moth vs. the bee?

Natural selection acts on variations

• There are three different types of natural selection that act on variation: stabilizing, directional, and disruptive.

Natural selection acts on variations

• Stabilizing selection is a natural selection that favors average individuals in a population.

Selection for

average size spiders

Normal variation

Natural selection acts on variations

• Directional selection occurs when natural selection favors one of the extreme

variations of a trait. Normal

variation

Natural selection acts on variations

• In disruptive selection, individuals with either extreme of a trait’s variation are selected for. Selection for

light limpets

Normal variation

Selection for

dark limpets

The Evolution of Species

• Significant changes in the gene pool could lead to the evolution

of a new species over time.

• The evolution of new species, a process called speciation occurs when members of similar populations no longer interbreed to

produce fertile offspring within their natural environment.

The Evolution of Species

• Geographic isolation occurs whenever a physical barrier divides a population.

• A new species can evolve when a population has been geographically isolated.

Reproductive isolation can result in speciation

• Reproductive isolation occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring

• A change in chromosome numbers- polyploidy can lead to speciation

Speciation rates• Gradualism is the idea

that species originate through a gradual change of adaptations

• Some evidence from the fossil record supports gradualism.

• In 1972, Niles Eldredge and Stephen J. Gould proposed a different hypothesis known as punctuated equilibrium.

• This hypothesis argues that speciation occurs relatively quickly, in rapid bursts, with long

periods of genetic equilibrium in between.