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Ch. 15 Darwin’s Theory of
Ch. 15 Outline
15-1: The Puzzle of Life’s Diversity
– The Voyage of the Beagle
– Darwin’s Observations
– The Journey Home
Ch. 15 Outline
15-2: Ideas that Shaped Darwin’s Thinking
– An Ancient, Changing Earth
– Lamarck’s Evolution Hypotheses
– Population Growth
15-3: Darwin Presents His Case
Publication of On the Origin of Species
Inherited Variation and Artificial Selection
Evolution by Natural Selection
Evidence of Evolution
Summary of Darwin’s Theory
Strengths and Weaknesses of Evolutionary Theory
The Puzzle of Life’s Diversity
Evolution: The process by which species
change over time
Theory: Well-supported testable
explanation. It explains a phenomena.
Voyage of the Beagle
Charles Darwin
– From England
– Joined the crew of the H.M.S. Beagle as the
ship’s naturalist
– 5 year trip around the world
– Darwin collected specimens at each stop
Voyage of the Beagle
Voyage of the Beagle
Darwin made numerous observations and
collected evidence that led him to propose
a hypothesis about the way life changes
over time.
– This hypothesis is now called the theory of
Darwin’s Observation
Patterns of diversity
– Many plants and animals seemed well suited
to their environment
– Organisms survived and reproduced in many
different ways
– Not all organisms lived everywhere
Darwin’s Observation
Living Organisms and Fossils
Darwin collected fossils
– Fossil: Preserved Remains of ancient
Some fossils didn’t resemble any living
Darwin’s Observations
The Galapagos Islands
– Off the west coast of South America
– The Location that most influenced Darwin
– Each Island had a different climate and
different organisms
– Noticed the birds had different shaped beaks
on each island and tortoises had different
shaped shells
Darwin’s Finches
The Journey Home
After returning back to England, Darwin
wondered if the birds he collected all
belonged to the same species at some
An Ancient, Changing Earth
James Hutton and Charles Lyell
– Developed the theory that the earth is very old. This
idea was contrary to what people thought at the time.
Hutton and Geological Change:
– Hutton was a geologist. He proposed that layers of
rock form very slowly and others are pushed up from
the sea floor to form mountains. (This takes a long
Lyell’s Principles of Geology
Lyell believed that the same processes that
changed the Earth in the past still operate in the
Darwin was influenced by Hutton and Lyell’s
work. He reasoned, if the Earth can change
over time (earthquakes, volcanoes) maybe life
can change too!
Lamarck’s Evolution Hypotheses
Before Darwin’s work, Jean-Baptiste
Lamarck observed that life changes and
the species descend from other species.
Lamarck’s Evolution Hypotheses
Lamarck had two ideas:
1. Organisms can alter their bodies by “use
and disuse”
Use: Use a structure and it will change
Disuse: Structures not used will disappear
2. Acquired characteristics can be inherited.
If you increase your muscle mass your children
will inherit your big muscles
Lamarck’s Evolution Hypotheses
Although Lamarck’s ideas were incorrect,
he was one of the first ones to realize that
organisms are adapted to their
environments and propose a theory of
Use and Disuse
Population Growth
Another influence of Darwin was Thomas
Malthus. This scientist published a book
in which he stated that babies were being
born faster than people were dying.
– Sooner or later food and living space will run
Population Growth
Darwin thought this applied to plants and
other animals even more because humans
usually only have one offspring at a time.
– So why wasn’t the Earth completely covered
in maple trees (for example)? Why were
some surviving and others not?
Darwin Presents His Case
After Darwin returned to England in 1836, he
continued to study his specimens. He
discovered that the birds from the Galapagos
were all finches, not wrens, warblers and
blackbirds like he thought (found nowhere else
in the world). The same was true for the
– All the species resembled ones on the South America
mainland, but they were a different species.
Darwin Presents his Case
Over 20 years later, Darwin published all his
findings in a book called, On the Origin of
Species. He didn’t publish it earlier because it
went against the common beliefs about
Not only did Darwin propose the theory of
evolution, he also proposed a mechanism by
which it happens:
– Natural Selection
Evolution by Natural Selection
Darwin realized the organisms competed
for resources (struggle for existence).
He noted that organisms better suited to
their environment (ex. Run faster, hide
from predators) survived to reproduce and
pass on their genes.
Evolution by Natural Selection
Fitness: The ability of an animal to survive
and reproduce
Adaptation: an inherited characteristic
that increases an organism’s chance of
Evolution by Natural Selection
Successful adaptations, Darwin
concluded, enable organisms to survive
and reproduce.
– Types of adaptations
Physiological processes
Evolution of Natural Selection
Survival of the fittest: individuals that are
better suited for their environment survive and
reproduce most successfully. (Natural Selection)
Over time, natural selection results in changes in
the inherited characteristics of a population.
These changes increases a species’ fitness in its
Evolution of Natural Selection
Darwin proposed that over long periods of time,
natural selection produces organisms that have
different structures. Species today look different
than their ancestors
Descent with Modification: Each living species
has descended, with changes from other
species over time.
Evidence of Evolution
Fossil Record
Geographic Distribution of Living Species
Homologous Body Structures
Evidence of Evolution
Fossil record-More Coming in Ch. 16
Geographic Distribution of Living Species
– Similar organisms found in different places on Earth
– Ex: Darwin’s Finches
– Organisms under the same “pressures” had similar
Homologous Body Structures
Structures that have different mature forms but
develop from the same embryonic tissues
– Ex. Wings and arms
– Help Scientist determine common ancestors
– Not all homologous structures serve important
Vestigial Organs: Organs reduced in size
(Traces of homologous organs in other species)
– Have little or no function
Homologous Structures
Ancient lobe-finned fish
Organisms that have similar
developmental stages as embryos are
more closely related to each other.
Summary of Darwin’s Theory
Individual organisms differ, and some of this variation
is inheritable
Organisms produced more offspring that can survive
and there is competition for limited resources
Individuals best suited survive and reproduce. Others
die or leave fewer offspring. This process of natural
selection causes species to change over time.
Species alive today are descended with modifications.