1. The Evidence for
Evolution

2. Evidence Supporting Darwin
 1) Fossil records
 2) Anatomy
 3) DNA
 4) Embryology

3. 1) Fossils
 Footprints of
dead organisms
 Tracks
 Insects trapped
in tree sap
 Impressions of
skin
 Traces of dead
organisms.

4. Conditions to create fossils
 Must be buried by sediments
 Swamps, mud, tar pits, ocean
bottoms
 Hard stuff most likely to be
fossilized.

5. How are Fossils Dated?
 Scientists determine the age of fossils by
measuring the amounts of radioactive
decay.
 Half-life describes how long it takes for one-
half of the radioactive atoms in a sample to
decay.
 The rate of radioactive decay is constant
 Scientists can use the amount of radioactive
element remaining in a rock or fossil to
determine its age. This technique is

6. 2) Anatomy
Transitional Species
– Evolutionary transitions/ intermediate
forms of the organism.
 Whales-
– Are descendants of 4 legged land
animals that are also ancestors of
horses and cows.

7.  35 mya
 42 mya
 50 mya
 60 mya

8. Whales- Vestigial Structures
-Remnants of an organisms
 Hind limbs
evolutionary past.
became
smaller
 Eventually lost
 Modern whales
have a pelvis
but, no rear
limbs.

9. Structural Evidence cont.
 Vestigial
Structures:
Remnants of an
organisms
evolutionary
past. Structures
reduce in size
and have no
present function.

10. Comparative Anatomy

11. Structural Evidence
 Comparing the way
two organisms are
put together.
 Homologous
structures:
Modified versions of
the same structure.
Similar in structure
differ in functions.

12. 3) DNA Evidence
 Structural, fossils, and developmental
evidence still posed many questions.
 DNA evidence supports the other three.
 If species change over time, their DNA
will also change.
 Similar organisms = similar DNA
 Genes accumulate more alterations in
their nucleotide sequence over time.

13. DNA Evidence con’t
 Compare: chimp, dog, rattlesnake,
human
 Protein- look at amino acid sequence.
 When comparing a.a. sequences
chimps vs. humans 0 a.a. differences
– Dog vs human 13 a.a. differences
– Rattlesnake vs. human 20 a.a.
difference

14. 4) Embryology
 Early stages of development are similar
between organisms.