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Evolution
Zoology Unit 2
Evolution
Evolution, or change over time, is
the process by which modern
organisms have descended from
ancient organisms.
Voyage of the Beagle
Charles Darwin – born in England
 Joined the crew of the
H.M.S. Beagle
 Sailed around the world
 Made numerous observations
and collected evidence that
led him to propose his
hypothesis.

Darwin’s Observations
Patterns of Diversity:
•
Puzzled by where different species lived and
did not live
•
Asked:
Why were there no rabbits in Australia,
despite the presence of habitats that
seemed perfect for them?
Why were there no kangaroos in England?
Darwin’s Observations
Living Organisms and Fossils
•
Darwin collected and preserved fossils
•
Fossils resembled organisms that were still
alive – other looked completely unlike any
creature he had ever seen.
He Asked:
Why had so many of these species
disappeared?
Darwin’s Observations
The Galapagos Islands
•
Most influenced Darwin
•
Although islands were so close together, the
islands had very different climates.
•
Fascinated by the land tortoises and marine
iguanas.
Darwin’s Observations
Galapagos Islands continued
•
Saw that giant tortoises varied in predictable
ways from one island to another.
•
The shape of a tortoise’s shell could be used to
identify which island a particular tortoise lived.
Natural Selection Questions
(Bill Nye)
1.
2.
3.
4.
5.
6.
7.
A young man that walked out was __ ___.
He quit medical school to become a ___.
How long did the Beagle stay in the Galapagos
Islands? __ days
Finches had different shaped ___: varied by
the environment they inhabited.
What was the mechanism that made evolution
occur? ___ ____
When did he publish his book?
Now, every where we look at today, we see
something that came from ___.
Natural Selection Clip
(Bill Nye)
The Origin of Species

The actual title is:
The Origin of Species by Means of Natural Selection
•
The book proposed a mechanism for
evolution that he called natural selection.
•
Presented evidence that demonstrating
the process of evolution has been taking
place for millions of year.
Darwin’s Arguments
Natural Variation and Artificial Selection
•
Argued that species were not perfect and
unchanging.
•
Natural Variation: There are differences
among individuals of a species.
Examples:
Some cows gave more milk than others & some
plants bore larger fruit than others.
Darwin’s Arguments
Natural Variation and Artificial Selection
Artificial Selection: Nature provided the
variation among different organisms, and
humans selected those variations that they
found useful.
* Only the largest hogs, fastest horses, and the
cows that gave the most milk were selected to
breed and produce offspring.
Evolution by Natural Selection

Survival of the Fittest: Process by which
individuals that are better suited to their
environment survive and reproduce most
successfully; also called Natural Selection.

Darwin called the ability of an individual to
survive and reproduce in its specific
environment fitness.

An adaptation is any inherited characteristic
that increases an organism’s chance of
survival.
Darwin’s Discoveries Video Clip
Survival of the Fittest

The concept of fitness, Darwin argued, was
central to the process of evolution by natural
selection.
Example:
Baby birds compete for food in the nest. The
stronger bird may take food from the weaker
siblings.
Evolution by Natural Selection
Descent with Modification: Principle that each
living species has descended, with changes,
from other species over time.
•
Implies that all living organisms are related to
one another.
Common Descent: The principle that says all
species – living and extinct – were derived from
common ancestors.
Evidence of Evolution
Fossil Record
Fossils that had formed in
the different layers of rock
were evidence of gradual
change over time.
One could view how a
species had changed and
produced different species
over time.
Evidence of Evolution
Geographic Distribution of Living Species
• Species now living on different
continents had each descended from
different ancestors.
• However, because some animals on
each continent were living under similar
ecological conditions, they were
exposed to similar pressures of natural
selection.
• They ended up evolving certain
striking features in common.
• This is called Convergent Evolution
Homologous Body Structures
Homologous Structures: Structures that have
different mature forms in different organisms
but develop from the same embryonic tissues.
Similarities in Early Development
In their early stages of development, chickens,
turtles, and rats look similar, providing evidence
that they shared a common ancestry.
Evolution
Analogous Structures
•
Analogous structures can be superficially
similar in construction, but are NOT inherited
from a common ancestor.
•
Example: The wing of an eagle & the wing of a
insect have the same function (both enable the
organism to fly) – but are constructed in
different ways & from different materials.
Analogous Structures
* While analogous structures do not indicate
close evolutionary relationships, they do show
that functionally similar features can evolve
independently in similar environments.
Vestigial Structures
•
Vestigial Structures are structures that are the
reduced forms of functional structures in
different species.
Examples:
1. Snake Pelvis: The pelvis is the attachment
point for legs and is therefore nonfunctional in
an animal without legs
Vestigial Structures
2. Kiwi Wing: The wings of kiwis are too small to
be of any use in flight
3. Human Appendix: Important for digestion in
many mammals, but of limited use in humans &
some apes
Adaptations:

Mimicry: Adaptation in which one species
evolves to resemble another species for
protection or other advantages.
Adaptations:

Camouflage: Adaptation
that allows organisms to blend
into their surrounds.