Evolution Notes Part IV
Evidence for Evolution
1. Fossil Evidence:
a. Fossil: preserved remains of an organism: soft or hard part
or imprint of an organism that has “turned” to rock
b. Fossil Record: Shows organisms that are no longer living and
how they have changed over time. A “written” history of life
1. Relative dating: A way of aging a fossil based on which
rock layer they are found in. Compare ages.
Index fossil: A fossil that is found over a wide range
but only lived for a short time.
2. Radioactive dating: A way of aging a fossil by measuring
the radioactive isotopes vs the stable atom content.
More exact dating.
d. Where are most fossils found?
Sedimentary rock. Lower level = older fossil.
2. Morphological Homology:
Similarities due to common ancestor
a. Homologous structures:
 Structures derived from a common ancestral structure.
Similar structure, may have different function.
ex. Arm of human, cat, horse, wing of bird, bat,
flipper of whale.
b. Analogous structures:
 A structure that is similar between different species
because it serves the same function but is not derived
from a common ancestral structure.
ex. Bird wing, bat wing, butterfly wing.
3. Embryology (Ontogenic) Homology:
 Comparing the developmental phases of embryos of different
 Organisms will have similar features during development if they
derived from a common ancestor. The more related they are, the
longer they share features. The less related, the earlier they
Ex. Humans have gills, tail, and webbed feet and hands as
an embryo.
4. Molecular Homology:
 Comparing amino acid sequences can reveal evolutionary
relationships. The more two organisms have in common,
the more closely related they are. Derived from similarities
in DNA.
5. Vestigial structures:
 Structures that have a marginal, if any use to an organism.
Reduced in size. Derived from an ancestor that
used/needed the structure.
 Ex. Pelvic bone in whales, femurs in pythons, appendix,
wisdom teeth, and tail bone in humans.
6. Biogeography:
o The study of the geographical distribution of organisms.
o Species that are related to each other often tend to live
o The fossils of a species ancestors will be found in the area
where a species is currently found.
o As geography changes, populations are separated or
combined with new populations.
-Continental movement, mountain formation, rivers
 What is a cladogram?
A chart that shows the development of particular traits and the
evolutionary relationships between different species.
o What causes a branch to appear? When a new trait
appears, a new branch will appear. All organisms after the
branch exhibit the trait while all organism before the branch
don’t have the trait.
o What does each branch point represent? A common ancestor