EVIDENCE SUPPORTING
EVOLUTION
Fossil Evidence & Biogeography
Homologous & Analogous Structures
Vestigial Structures
Embryology
Molecular Comparisons
Microevolution in Action
Paleontological Evidence
(The Fossil Record)

A record of all fossils ever discovered which
demonstrates the changes in organisms’ structures
over time

Transitional forms (missing links) have been found
to show relationships between ancient forms and
modern ones

Fossils can be dated radioactively to determine
their age accurately
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html
Biogeographical Evidence: Convergent
Evolution

Unrelated species living in different regions of the
world with similar environmental features happen
to look alike (analagous)

Supports natural selection concept: adaptation to
environmental factors
Biogeographical Evidence
Example: Unrelated anteaters around the world share common features
because of their common selective pressures (food, climate, etc…)
Comparative Anatomy
Homologous Structures

Structures on different species which are similar in
form, but different in function

Structures indicate a shared common ancestor

Example:

The arm bones of various vertebrate organisms
Homologous Structures
Comparative Anatomy cont…
Analogous Structures

Features that share identical functions and look
similar in build due to natural selection

Internal anatomy is very different; organisms are
not closely related

Examples: bird and insect wings (i.e. hummingbird
& hummingbird moth)
Vestigial Structures

Structures that remain on an organism which have
no purpose, or are not used for their original purpose
anymore

Examples:

Whale/snake hip bones

Ostrich wings

Human tailbone,wisdom teeth, appendix
Whales have a pelvis (hip bone) and a femur
(upper leg bone) but they have no need for them in
the water
Flightless birds, like this Cassowary and
Ostrich have vestigial wings
The human tailbone or coccyx
doesn’t do much for us –
except hurt if you land on it.
These are left-overs from
ancestors who used tails for
balance or communication like
many mammals do today.
Some children are born with a
full tail (since we have the
genes for it). Those who have
had to have it surgically
removed don’t suffer any
negative health effects without
it.
Human wisdom teeth: the rear molars that most
(but not all) people must have removed when
they grow in right around age 18. Left-overs
from a larger mouth or a byproduct of better
modern hygiene?
The human appendix: a vestigial organ that is still used
by other, mostly herbivorous mammals to help them
digest plants in their diet. It is thought to be a leftover
from ancestors with a more herbivorous diet. Now it is
more a nuisance than anything.
They commonly
become infected
causing appendicitis
and must be
surgically removed.
Embryological Evidence

Embryos of a different organisms
look extremely similar at early
stages of development -similarities
begin to fade with further
development
Molecular Evidence

Organisms share a great deal of the same DNA or proteins

The closer an organism is to it’s ancestor, the more
molecular similarities exist


Humans/Chimps = 98% the same DNA

Blood proteins in humans & gorillas differ by only one amino acid!

Some genes are almost identical in most of the animal kingdom
One organism’s molecular sequences can work in another
organism

Human DNA can make yeast work!
Evolution in Action

Kettlewell’s Moths: England’s industrial revolution killed
tree lichen and added soot to trees, allowing the
population of peppered moths to shift in favor of the black
variety (previously rare mutation)
Evolution in Action: Speciation
Divergent Evolution

Darwin’s Galapagos Finches