Transcript Fossils – Evidence?

What Scientists Agree On
• Scientists believe they can explain the
diversity of species on Earth given the
following three statements:
– Earth is about 4.6 billion years old
– Organisms have inhabited Earth for most
of its history
– All organisms living today have evolved
from earlier, simpler organisms
Fossils – What are they?
• Fossils = preserved or
mineralized remains or imprints
of an organism
– Remains included bone, tooth,
petrified tree, or shells
What Fossils Tell Us
• Paleontologists – study fossilized
remains
• Paleontologists can date fossils using
radiometric dating to put fossils in
order from oldest to youngest
-Carbon dating
• Orderly patterns of evolution can be
seen
Fossils – Evidence?
• Provide an actual record of Earth’s past life
forms (evolutionary record)
• Shows that species have changed over
Earth’s history. Evidence of extinct species.
140 million years
800 million years
Intermediate Fossils
• Intermediate fossils provide links
between older and newer species –
commonly known as “Missing
Links”
• Many intermediates have been
found:
– Fish and Amphibians
– Reptiles and Birds
– Reptiles and Mammals
Intermediate Fossils
• In 1990, intermediate
whale fossils were
discovered
• Evidence shows that
whales evolved from 4legged land mammals
Why We Don’t Have More
Fossil Clues
• Fossils are produced when
organisms are buried in fine
sediments deposited by water,
wind, or volcanic eruption
• What kinds of conditions are
helpful for fossil formation?
• Wet, shallow areas, marshlands,
clay
• (Need these “perfect”
conditions for fossils to form)
Why We Don’t Have More
Fossil Clues
• Organisms living in upland
forests, mountains, grasslands,
or deserts are not easily
fossilized
• Even those organisms buried in
the right conditions have a slim
chance of being fossilized
before the body decays
– Exoskeleton vs. soft body
Anatomy Development
• Comparison of different body
structures between organisms show
similarities in structure even though
they may have different functions
Homologous Structures
• Remember the term homologous?
• Similar structures between organisms
developed from the same basic groups
of bones
• Similar structure, with same or
different functions.
Homologous Structures –
Evidence?
• Homologous structures show that
organisms share a common ancestor
• Show change occurring to already present
structures (divergent evolution)
Analogous Structures
• Opposite of homologous structures:
• Similar function, different structure
• Examples:
– Bat wing and butterfly wing
– Both used for flying (function), different bone
structure
Analogous Structures – Evidence?
• Same type of adaptations can be selected
for in separate environments if selective
pressures are similar  NATURAL
SELECTION WORKS!!!
• Convergent Evolution
Vestigial structures
• Structures that were useful at one time,
but no longer serve a function.
• Examples: tail bone, appendix
Evidence
• Ancestor we descended from may have
used it – left over from the course of
evolution
Biological Molecules Contain
Evolutionary Record
• If species have changed
over time, we should see
genetic changes
associated with the
change
• Study proteins and
nucleic acids for clues
DNA Evidence
• Nucleotide changes cause changes in
amino acid sequences
• GATAACCAAGAATTATTAGCGAGA
• GATAACCAAGAACTATTAGCGAGA
• Scientists can determine how closely
organisms are related by examining the
number of nucleotide changes
(mutations) in their DNA
Proteins
• Proteins are made up of chains of amino acids
– Amino acid sequence is genetically determined
– This information is used to construct evolutionary
histories
• Species that have evolved more recently
share similar amino acid sequences than
species that branched apart many millions of
years ago
Relationship to Humans
Protein Cytochrome-C
Species
Amino Acid
Differences
Gorilla
1
Rhesus Monkey
8
Mouse
27
Chicken
45
Frog
67
Lamprey
125
Recent Branch = similar amino acid
sequence
Old branch = different amino
acid sequence
Embryo Development
• Many related species have embryos that
resemble each other – fertilized eggs go
through similar patterns of development
• Develop tail, buds for limbs, and
pharyngeal pouches (become gills in fish
and amphibians)
– Tail in humans disappears before birth =
tail bone
– Pharyngeal pouches develop into other
structures
Crash Course - Evidence for
Evolution