1. III. Darwin Presents His Case
A. Publication of On the Origin of Species
*Darwin studied his findings but
didn’t publish them right away
because they were so controversial.
1858 – Darwin receives essay from
fellow naturalist Alfred Russel
Wallace summarizing the same ideas
as Darwin’s evolutionary theory.
-Both men present their ideas
together & in 1859 Darwin publishes
his book, On the Origin of Species.

2. B. Inherited Variation & Artificial Selection
*Darwin’s most important
observation was that individuals
within a species vary from each
other.
-Darwin learned that variation is
heritable----We know
specifically from our genes.
-Breeders use variation to
develop the best crops &
animals. Darwin termed this
artificial selection.
Artificial selection – selection by
humans for breeding of useful
traits from the natural variation
among different organisms.

3. C. Evolution by Natural Selection
*Darwin compared artificial
selection to nature & found
that there was :
1. Struggle for existence – when
members of each species
compete regularly to obtain
food, living space, & other
necessities of life, ex : faster
predators catch food & better
protected/camouflaged prey
survive.
2. Survival of the Fittest – when
individuals that are better
suited to their environment
(have best adaptations)
survive & reproduce most
successfully.

4. C. Evolution by Natural Selection
Fitness – ability of an individual to
survive & reproduce in its specific
environment.
Adaptation – any inherited
characteristic that increases an
organism’s chance of survival.
Successful adaptations allow
organisms to become better suited
to their environments, ex : can be
anatomical or structural
characteristics like sharp quills on
a porcupine, physiological
processes/functions, or behavior.
-Darwin referred to survival of the
fittest as natural selection because
of its similarity to artificial
selection.

5. C. Evolution by Natural Selection
3. Descent With Modification – principle that each living species has descended,
with changes, from other species over time.
-It implies that all living
organisms are related to each
other through common
descent.
Common descent – principle
that states that all species,
living & extinct, were derived
from common ancestors.

6. D. Evidence of Evolution
*Darwin believed that
organisms had been
evolving on Earth for
millions of years.
-His evidence for this
process was in the fossil
record, geographical
distribution of living
species, homologous
structures of living
organism, & similarities in
early development, or
embryology.

7. The Fossil Record
1. The Fossil Record – shows ancient life that was on Earth. By comparing older & newer rock fossils, scientists can see how life on Earth has changed over time.
Fossil – preserved remains of
ancient organisms.
*Fossil record can’t be
considered solid proof of
evolution because it is
incomplete, there are gaps
in it.

8. Geographic Distribution of Living Things
2. Geographic Distribution of Living Things - Darwin found different species of animals living in similar environments throughout the world.
-He realized that although different,
many of these organisms had common
features.
-He concluded that similar ecological
conditions & exposure to similar
pressures of natural selection
had caused development of similar

9. Homologous Body Structures
3. Homologous Body Structures – anatomical similarities among the body parts of animals.
Homologous Structure – structures that have different
mature forms in different organisms but develop from the
same embryonic tissues, ex : when comparing
arms/legs/wings/flippers, all vary in form/function but
are constructed of the same basic bones.

10. Analogous Structures
Analogous Structures – structures found in different
types of organisms that are similar in function or outward
appearance but dissimilar in basic structure or
embryological development, ex : insect vs. bird wing.

11. Vestigial Organs Vestigial Organs – organs that serve no
useful function in an
organism, ex : human
wisdom teeth &
appendix.

12. E. Similarities in Embryology
*Many animals have similar
embryos.
Embryology – the study of an
organism before birth.
-Similarities exist greatly between
the embryos of vertebrates
(animals with backbones), ex :
human, fish, chicken.
-Such similarities suggest common
ancestry because the same groups
of embryonic cells develop in the
same order & in similar patterns to
produce the tissues & organs of all
vertebrates.

13. Extended tail-like vertebrae