Evolution
Evolution
The theory of evolution is the theory of change in a
population over time.
Recall that a scientific theory is a well-tested
framework, or explanation of facts and laws.
The following is a collection of evidence supporting
the theory of evolution.
Evidence for Evolution
1. Fossils
- trace of long-dead organism
- can tell us what kind of organisms
existed at various times in Earth’s history,
where they lived, their behavior, and
extinctions.
- record is incomplete (has “missing
links”)
Evidence for Evolution
In 2006, scientists found the “missing link” between fish
and amphibians. Tiktaalik has strong bony fins, which
could have helped it walk on land.
How to date a fossil:
• Relative dating- can tell if a fossil is older
or younger than another fossil
• Absolute dating- uses radioactive molecules
in the body (like C-14) to estimate the age
of the fossil in years
– Ex. Half-life of C-14 is 5730 yrs
16 g  8 g  4 g  2 g
5730 yrs
5730 yrs
5730 yrs
Relative vs. Absolute Dating
Evidence for Evolution
2. Adaptations – anything that allows an
organism to survive better in its
environment
- Ex.: thorns, claws, mimicry (resembles
harmful organism), camouflage (blending in
with environment)
Evidence for Evolution
3. Anatomical structures
- Some very different organisms have very
similar bone structure (analogous &
homologous features)
- Also, some organisms have structures with
no present-day use (called vestigial
structures) that suggests their ancestors
might have used them. Ex.: appendix
The legs of a skink are
vestigial structures.
Homologous Body Structures
Body Structures that
have the same
internal structure,
BUT, provide
different functions
for the different
organisms. Thus,
may indicate these
organisms came from
a common ancestor.
Analogous Body Structures
Analogous Structures -
pertain to the various
structures in different
species having the
same appearance,
structure, or function
but have evolved
separately, thus do
not originate from a
common ancestor.
Vestigial Body Structures
Vestigial Structures are
structures (either internal or
external) that have no present
day use. This is a type of
evidence that gives clues
about the activities,
appearance, or ancestry of an
organism.
* This is why a surgeon can
remove your appendix
without causing any harm!
Geographic Distribution of
Living Species
• Different Animals On
Different Continents
But Similar
Adaptations To
Shared Environments
Similarities In Early
Development
• Embryonic Structures Of Different
Species Show Significant Similarities
• Embryo – early stages of vertebrate
development
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
Human Fetus – 5 weeks
Chicken
Rat
Turtle
Evidence for Evolution
4. Biochemistry similarities
- Comparison of DNA/RNA/proteins from
different organisms shows how closely they
are related.
Similarities in DNA Sequence