1. Fossils 2. Geographic Distribution 3. Homologies

Evidence ofEvolutio

n

FOR EVOLUTION

1. Fossils2. Geographic Distribution3. Homologies

Evidence of Evolution

1st type of EvidenceFOSSILS

What is a fossil?-The preserved remains of a once-living

organism.

Fossil Record

How do fossils help scientists?

1. Tells us what organisms lived long ago

2. Shows how the Earth’s surface has changed.

3. Help us understand what past environments may have been like.

Over time, more sediment layers build on top of the remains. Minerals replace all or part of the organism’s body.

The preserved remains may later become exposed by erosion or the Earth’s movement.

How do we get fossils?Fossils are formed in SEDIMENTARY ROCK.If an organism dies and is buried by sediment rock, it’s bones are protected from rotting.

You have to DATE them!

How do we know the age of fossils?

1. Relative DatingAge of fossils RELATIVE to

other rocks or fossils.

2. Radioactive datingACTUAL age of fossils using the half life

of radioactive isotopes

Which fossil came first?

How does Relative Dating work?

AB

C

D

E

Rock layers form in order of age – the oldest layers on the bottom and the youngest on the top.

Scientists use index fossils to compare the ages of fossils.

Index fossil: a species easily recognizable, existed for a short period of time, and wide geographic range.

*** Does NOT give age in years***

How does Relative Dating work?

AB

C

D

E

Looking at this mountain, where would you expect to find the oldest fossils?

Index Fossils Found Fossils

Which is older B or D?

SAME AGE

Throughout an organism’s life, it takes in Carbon-14.

Once the organism dies it no longer takes in Carbon-14.

The C-14 present in the plant or animal begins to decay at a certain rate called half-life.

Half-life: the length of time required for half the radioactive atoms in an organism to decay.

How Does Radioactive Dating Work?

Carbon-14 half life: 5,730 years

Years from Present

0 5,730 11,460 17,190 22,920 28,650 34,380 40,110 45,840 51,570

Percent of Original C14 Remaining

100 50 25 12.5 6.25 3.13 1.56 0.78 0.39 0.20

Decay of Carbon-14

What do you notice about the percent of original C-14 remaining?

What are the scientific explanations for data showing periods of stasis and

sudden appearance in the fossil record?

The fossil record suggests that evolution has proceeded at different rates for different

organisms at different times.

Gradualism

The idea that evolution involves a slow, steady change in a particular line of descent.

STASISShowing very little change over

time

Example: Horseshoe crabs

Punctuated equilibriumDefinition-Stable periods interrupted by rapid changes

Rapid Evolution may occur because:

A) small pop becomes isolated from the large population

B)small group migrates to a new environment--FINCHES

2nd type of EvidenceGeographic Distribution

Similar animals living in different locations are the product of different lines of evolutionary descent.

Geographical Distribution

3rd type of EvidenceHomologies

3 types of HomologiesAnatomicalMolecular

Developmental (embryology)

Homologous Structure: structures that have different mature forms but develop from the same embryonic tissues.

Homologous Structures

Homologous structures provide strong evidence that all four-limbed vertebrates have descended,

with modifications, from common ancestors.

Not all homologous structures serve important functions.

Vestigial organs: Organs in animals that are reduced in size to where they are just traces of homologous

organs in other species.

Homologous Structures

Analogous Structure: the similarity of structure between two species that are

not closely related.

Analogous Structures

Which structures are analogous?

Homologous?Answer:

Analogous- Bird to Insect, Bat to Insect

Homologous- bird and bat wings

Convergent Evolution: Species from different evolutionary branches may come to resemble one another if they live in very similar environments.

Natural Selection may result in body structures and even whole organisms that look very similar

without having the same common ancestor.

How do Analogous Structures Occur?

Comparative Embryology: the comparison of early stages of development

Pharyngeal (throat) pouches in embryotic

stages shows one sign that vertebrates evolved from a

common ancestor.

EmbryologyPig Cow Rabbit Human

Molecular Biology studies amino acid sequences of similar proteins in different

species to discover the molecular history of evolution and common ancestor.

Molecular Biology

Molecular Biology is the BEST WAY to determine how closely species are related

to one another.

Molecular Biology

Species 1 ATGTAGCTG

Species 2 ATCTGACTC

Species 3 AGGTACCAG

Species 4 AGGCGGCAG

Which two species are most closely related based on

these nucleotide sequences?