Chap. 15 : Darwin’s Theory of
Evolution
I.
Fossils
- traces of dead organisms, collect
in sediments (dust, mud, etc) to
form sedimentary rock.
A. Types :
 1. Mold – imprint (living parts maybe left behind)
common in limestone rock.
 2. Cast – when molds fill in with minerals
 3. Amber – fossilized sap or petrified rocks
B. Law of Superposition – states that layers of
succession (called strata) build on top of each
other.
youngest
D
C
B
oldest
A
** all fossils found in same area are from the same time
period.
** relative age – comparison between fossils.
** absolute age - determined by radioisotopes.
(carbon dating)
C. Succession layers – shows periods of
boom of certain organisms then periods of
mass extinctions. Caused by environmental
changes.
 D. Biogeography – the study of distribution
of living (or once living) organisms.
II. Evolution Theories
A. Lamarck – 1st to suggest that similar
species arose from common ancestors.
 Suggested the term acquired trait ( not passed by
genes but changed by habitat or behavior and
then passed to offspring). Ex. webbed feet –
resulted from repeated stretching.
B. Darwin – “Origin of Species” – book about the
idea of natural selection (nature selects for the
most fit organisms to survive)
- fitness – how well an organism is adapted to its
environment
III. Evidence of Evolution
 A. Homologous/Analogous Structures
- Homologous Structures – features that
originated from a shared ancestor. Ex. Different
beaks, forelimbs of penguins, alligators, bats, and
humans.
** indicates that different species shared a
common ancestor
- Analogous Structures – features that look
somewhat alike and serve similar functions but do
not share the same embryo development. Ex.
Birds and moth’s wings.
B. Vestigial Structures – structures that
presently serve no function.
 Ex. Appendix and tail bone in humans, 4chambered stomach in whales, “legs” in boas and
pythons.
--- organisms with similar vestigial structures shared
an ancestor
C. Similar Embryo Development
- in the early stages of development all
vertebrates are the same. Ex. Fish,rabbits,birds,
and humans
D. Similar Macromolecules – homologous
structures have similar amino acid sequences.
The # of differences are related to how recent
their ancestor was.
IV. Patterns of Evolution
1. Coevolution – change of 2 or more
species in close association with each other.
Ex. Predator/prey , plants/animal pollinators
-- bats and flowers – bats long tongue and
slender nose, flower light in color and smells
fruity
2. Convergent evolution – environment selects
similar phenotypes even though the ancestors were
quite different. Ex. Sharks and porpoises
3. Divergent Evolution – 2 or more related populations
become more and more dissimilar. Caused by a change of
habitat.
--- usually results in new species
a. Adaptive Radiation – related species evolve from
single ancestor. Ex. Darwin finches.
b. Artificial selection – speeding up of divergence by
artificial means. Ex. Domestic dogs, horses
-- doesn’t result in new species but rather varieties of
species.
V. Events that lead to new species :
 Barrier separating like organisms forms
(flood, volcanic eruptions, earthquakes,
forest fires, etc.)
 Time passes (thousands of yrs),
environment changes
 Natural selection breeds changes
 Enough change occur overtime to change
DNA significantly so no longer recognized.
VI. Primates and Human Evolution
45 million years ago
New World
Monkeys (tails
that grasp,
upward noses)
monkeys
Old World
Monkeys (nongrasping tail,
downward nose)
baboons
Some evolved into
apes and gorillas
Evolved into
humans