Chapter 15
Darwin’s Theory of Evolution
Section 15-1 – Puzzle of Life’s Diversity
Biological Diversity – variety of living things
• How did all these organisms come to be?
• How are they related?
Evolution - change over time; the process by
which modern organisms have descended
from ancient organisms
• Change in a population of organisms over
generations
I. Voyage of the Beagle
A. Charles Darwin
1. Born 1809
2. Attended Cambridge - Studied natural
history, geology
3. After college, joined the crew of the H.M.S.
Beagle.
•
His observations & collected data led to him
proposing evolutionary theory
II. Darwin’s Observations
A. Patterns of Diversity
1. Plants & animals seemed remarkable well
suited to their environment
2. Types of organisms are found in only
certain areas of the world
•
Argentina & Australia have grasslands. So why
don’t they have the same organisms living
there?
B. Living Organisms & Fossils
1. Darwin also collected fossils (remains of
ancient organisms)
•
What are some different types/examples of
fossils?
2. Some fossils resembled current, living
organisms, while others looked completely
different
•
•
Why had some species disappeared?
How are they related to living species?
C. The Galapagos Islands
1. Found 13 species of finches that were similar
except for their beaks
2. Each Island had different food sources, requiring
different beaks!
3. Also noticed different species of land tortoises
on different islands.
4. The shape of a tortoise’s shell differed from
island to island. See pg. 371, Figure 15-3
Figure 22.6
(b) Insect-eater
(a) Cactus-eater
(c) Seed-eater
Section 15-2: Ideas that shaped Darwin’s Thinking
I. The Beliefs of the Time
A. Earth & all life had only been created a
few thousand years ago
1. No organisms had changed, but the robin had
always been a robin
B. As fossils record grew, adjustments to
beliefs began
1. Periods of creation occurred following
catastrophic events that killed off many forms
of life
II. An Ancient Changing Earth
A. James Hutton
1. Proposed theory of Gradualism where by Earth’s
features were created (& changed) gradually by
natural processes over time
2. Mountain building, valleys, canyons, oceanic
ridges, etc. occur over millions of years
3. Proposed Earth was much older than a few
thousand years.
B. Charles Lyell
1. Before his journey, Darwin was given Lyell’s book,
Principles of Geology
2. Incorporated gradualism into uniformitarianism,
which states that geologic processes operate
today just as they did for most of Earth’s history
3. Influenced Darwin!
• If the Earth could change over time, might life
change too?
• If so, life would change slowly, over millions of
years, just like the Earth.
C. Jean Babtiste de Lamark – 1st to hypothesize
on evolution
1. Similar species descended from a common
ancestor. Meaning all similar species
come from one ancient species.
2. New species develop through the passing
of acquired traits, which are traits not
determined by genes, but by the
environment.
3. According to Lamark, species acquire traits
because/by:
•
•
All organisms acquire traits that help them live
more successfully in their environment
Using/not using certain parts of their body to
change the size/shape of organs
– Ex: A water acquired webbed-feet by stretching
the membrane between its toes. Every offspring
of this bird will have webbed feet.
– Ex: A person is blinded in an accident. This
acquired trait will be passed on to offspring.
Does this make sense?
Are acquired traits passed on?
NO
NO
C. Lamark’s theories Disproved/Proved
1. Acquired Traits are not passed on to offspring,
only genetic traits are!
2. Similar species do tend to share a common
ancestor and organisms do change over time.
D. Thomas Malthus – observed that babies
were born faster than people or dying
1. If the human population grows
unchecked, living space & food will
become insufficient.
2. Darwin applied this concept to
plants/animals.
•
•
•
1 maple tree produces 1000’s of seeds a year
Not all survive = many offspring die before
reproducing
What factor(s) determines who survives &
who doesn’t?
Section 15-3: Darwin’s Theory of Evolution
I. The Race to publish
1. Alfred Wallace also proposed a theory on
evolutionary change, sent the essay to
Darwin
2. Drove Darwin to write out and publish his
theory ……. before Wallace.
3. 1859, published On the Origin of Species:
By Means of Natural Selection
II. Natural Variation & Artificial Selection
A. Natural variation is differences among
individuals of a species in nature
1. This variation could be inherited.
2. Darwin noted that breeders used variation to
improve their crops, livestock through a
technique called selective breeding.
B. Darwin termed this process as artificial
selection
1. Nature provides the variation, and humans
select those variations that they find useful.
III. Evolution by Natural Selection
A. Struggle for Existence
A. Members of each species struggle to exist by
competing for food, living space, etc.
B. Survival of the Fittest
1. Fitness: ability of an individual to survive and
reproduce in its specific environment
2. The fitness is the result of adaptations,
inherited characteristic that increases an
organism's chance of survival.
• Anatomical/structural, characteristics,
organism’s physiological processes or
functions, or complex features (behaviors).
3. Darwin referred to the survival of the fittest as
Natural Selection
• Successful adaptations = organisms become
better suited to their environment = better
able to survive & reproduce.
• Unsuccessful characteristics = organisms not
well suited to their environment (low levels of
fitness) = death or few offspring.
4. Natural Selection
• The traits being selected increase over time &
contribute to an organism's fitness in its
environment.
• Takes place without human control or direction.
• Cannot be seen directly; it can only be
observed as changes in a population over
generations.
C. Descent with Modification – Each living
species has descended, with changes, from
other species over time
1. As a result, species today look different from
their ancestors.
2. Also implies that all living organisms are related
to one another.
3. Common Descent: All species—living &
extinct—were derived from common ancestors
4. a single “tree of life” links all living things.
Darwin’s
Tree of Life
IV. Evidence of Evolution
A. Fossil Record
1. Fossils formed in different rock layers showed
that organisms have changed over time.
2. Fossils from sequential rock layers could show
how a species changed and produced a new
species!
B. Geographic Distribution of Living Species
1. Darwin’s finches in the Galápagos were similar,
yet different from one another & also different
from a similar species on the mainland.
2. Darwin’s finches could have descended with
modification from a common mainland ancestor.
3. Entirely different species of animals living in similar
environments can have similar
structures/behaviors
• descended from different ancestor.
• Living under similar ecological
conditions, being exposed to
similar pressures of natural
selection, they ended up
evolving common features.
4. Regardless of appearance, two species are closely
related when they share a common ancestry.
C. Anatomical Evidence
1. Homologous structures: Body parts with same
basic structure but different function
• Structures have different mature forms but
develop from same embryonic tissues
• Indicates common ancestry
• Foreleg – same set of bones for vertebrate.
C. Anatomical Evidence
2. Analogous Structures - Body parts with similar
function but different structure
• Indicates NO common ancestry
• e.g. wings if insect and wings of bat
C. Anatomical Evidence
3. Vestigial Structure: structure reduced in size
• No known function
• Left over from other structure
• e.g. tailbone for humans
D. Embryological Evidence – Compares
development of embryos
1. Similar embryologycommon ancestry.
2. Embryo looks similar for longer period = more
closely related species
3. Embryonic cells develop in same order and pattern
to produce tissues and organs which produce
homologous structures
E. Biochemical Evidence
1. The sequence of amino acids that make up
proteins are similar similar DNA
strandsorganism show evolutionary
relationship.
2. e.g. Humans and Chimpanzees (97% similar)