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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?