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Chapter 15Darwin’s Theory of Evolution
Essential Question:
What evidence did Darwin use to develop his theory of evolution?
15-1 The Puzzle of Life’s Diversity
How did life change from a prokaryote
to all of this in
4.6 billion years?
What is a theory? How does this relate to evolution?
• Theory is –– A well supported hypothesis.
There is A LOT of data and observation that supports a theory.
• Evolution is a theory – It is used to describe the
processes by which modern organisms have descended through time from ancient organisms.
Charles Darwin
• born in 1809, the same birthday as Abraham Lincoln
• In 1832, after graduating from college, sailed around the world aboard the HMS Beagle working as an unpaid naturalist
• this voyage changed his thinking about natural history and changed the course of science
Voyage of HMS Beagle1832 (technically Dec. 27, 1831) - HMS Beagle set sail to travel the world
– Aboard was Charles Darwin
– There to study plants and animals in South America, Africa, and Australia.
Darwin’s Observations
1. Patterns of Diversity
2. Living Organisms and Fossils
3. The Galapagos Islands
1. Patterns of Diversity• These
ladybugs are members of the same species yet their coloration varies.
• Why is this important?
Diversity on Earth
• Many different kinds of organisms
• Each is suited for its environment
• These traits that make them well suited are called adaptions
Variation can lead to diversity
• Cheetahs vary in speed.
• Can lead to starvation
Darwin’s Influences?
Observations of Adaptations
• collected samples and
observed species in
their natural
environment.
• noticed that organisms
tended to be well
suited ( adapted) to
their environment.
http://www.terraquest.com/galapagos/wildlife/island/finch.html
2. Living Organisms and Fossils
Living Organisms and Fossils
• Darwin wondered why the animal species he saw in the fossil record had disappeared?
– What processes were leading to the loss and rise of species?
– Why did they look similar, but exhibit changes through the fossil record?
3. The Galapagos Islands
What are adaptations? How does variation lead to adaptation?
• Inherited traits that increase a population’s chances of survival and reproduction are called ADAPTATIONS
Type of Adaptations Observed in Animals
• Physical– camouflage, mimicry
– Defense: spines, quills, armor
• Chemical– Smells, poisons, venom, sap, sprays
• Behavioral– Innate and learned
– Migration, hibernation (torpor)
– Courtship rituals
Biodiversity: Global Village• The variety and abundance of
different species is called
BIODIVERSITY.
• Earth is estimated to have
5 million to 30 million different
living species.
• Estimates suggest that 99% of all
organisms that ever lived are now
extinct.
Scientists over time began to ask questions
• Why is there such incredible Biodiversity?
• Why have so many species come and gone?
One man’s quest for an answer led to perhaps the most revolutionary theory in the history of science. . .
15-2 Ideas That Shaped Darwin’s Thinking
Essential Question: How did past scientists thinking help with Darwin’s
idea of Evolution?
How did Darwin develop his theory of
Evolution?
What were his 3 major influences?
Influence 1: An Ancient Changing Earth
• James HuttonProposed
• Earth is shaped by geological forces
• These forces take millions of years
• Therefore Earth is millions of years old, not thousands
• Charles LyellPublished
• Principles of Geology which Darwin read while aboard the HMS Beagle
• Explained the mechanisms for geological change
• Insisted scientists must make modern observations to explain past events
How did this influence Darwin?
Geology
• the geology work of Charles Lyell and James Hutton
• geological evidence suggested Earth was very old
• reasoned that if the Earth changed over time, these
changes would influence plant and animal life.
• fossil evidence seems to support this.
Influence 2: Lamarkian Evolution
• Jean Baptiste Lamarck
– Developed one of the first evolutionary hypotheses in 1809
– Did not believe all creatures shared a common ancestor
Lamarck’s Evolution Hypothesis
• 3 Parts
– Tendency towards Perfection
– Use and Disuse
– Inheritance of Acquired Traits
Part 1. Tendency Towards Perfection
• Organisms strive to improve themselves throughout their lifetime
Part 2. Use and Disuse
• Used body structures remain and develop: and unused body structures waste away
Part 3. Inheritance of acquired traits
• Characteristics acquired during the lifetime of an organism could be passed to offspring.
tommee.glogster.com
Darwin Didn’t Buy It• He questioned prior ideas and
sought a better explanation
Influence 3: Thomas Malthus
• Economist Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone
• All populations eventually exceed
the supply of resources (living
space and food)
• Populations would eventually be
limited by disasters such as
starvation, drought, war, etc.
• Remember what you learned in
Chapter 5!
http://www.rifpd.org/Family_Planning/Reproductive_Health/Infant-dying-starvation.jpg
Darwin Influences?
Population Control
http://www.design4effect.com/soc11/pop.htm
Application to Darwin
• Darwin noticed species will over produce offspring.
• Most die off.
• What causes the death of so many individuals?
15-3 Darwin Presents His Case
Essential Question:
What evidence of evolution did Darwin present?
How does natural selection lead to evolution?
Charles Darwin’s
Theory of Evolution
published in 1859
On the Origin of Species
by Means of Natural
Selection
Portrait of Charles Darwinwww.lib.virginia.edu/science/parshall/darwinport.html
The Origin of Species
• When Darwin returned from his voyage, he hesitated to publish work.
• Finally published his book in 1859 when learning colleague was working on the same topic.
Sources of Heritable Variation
• 4 Sources of Variation
– 1. crossing over
– 2. independent assortment
– 3. recombining of egg and sperm
– 4. random mutations
Fitness
• Species that are more adapted to their environment are have better ‘fitness’
• Which animal fitness is higher to live in the desert?
Natural Selection
• The “survival of the fittest”
• The process where organisms that are better suited for their environment tend to survive and produce more offspring
Natural Selection: 4 Steps
• 1. genetic variation must be present within a population
• 2. some variations must be more favorable and allow organisms to survive and reproduce
Natural Selection: 4 steps
• 3. survival must be differential
• 4. favorable traits must be inherited by offspring
So, what was Darwin’s Big Idea?
• the theory that species descended from more ancient forms of life through structural and physiological modifications as a result of natural selection of traits
What evidence exists in support of this idea?
Evolution as a result of Natural Selection
Types of Modern and Historical
Evidence for
the Theory of Evolution:
1. fossil record
2. chemical similarities
3. structural similarities
4. geographic distribution of species
Evidence for Evolution:Fossils
• Fossil – Formed by ancient plants or animals
• Older fossils are found under newer fossils
• Paleontologists study fossils for clues.
• FOSSILS are the preserved remains or imprints of ancient organisms.
/www.burgess-shale.bc.ca/gallery/gallery.htm
The Fossil Record
• Remains of plants and animals found in sedimentary rocks
• Some extinct species had traits that were transitional between major groups of organisms
• Confirms that species are not fixed.
Evidence of change and extinction?
Evidence of Habitat Change
• most common fossils
found in sedimentary
rocks are from the hard
parts of organisms,
including shells, bones,
teeth, and woody stems.
http://www.sdnhm.org/research/paleontology/images/otaywhale-rac26sept2001-2b.jpg
Not just bones
• Fossils are not always the
body parts of an organism.
A mold is a type of fossil
in which an impression of
the shape or track of an
organism has survived
Freezing
Amber
Impressions
The Fossil Record
• Fossils can be dated using: – radioactive isotopes– relative dating based on
their position in the sedimentary rock
• Video Shorts you can watch at home!
http://bioweb.cs.earlham.edu/9-12/evolution/HTML/live.html
Structural Similarities
• Homologous Structures
– Structures that are embryologically similar, are called homologous structures.
– This suggests that these animals evolved from a common ancestor.
Structural Similarities
• Structures that are similar in function but different in structural origin are called analogous structures
• They are not inherited from a common ancestor.
Examples of analogous structures include:
• Insect wings and bird/bat wings – both are used for flying, but are not from the same genetic origin
Similar in Appearance and Function
Homologous or Analogous?
Similar in Appearance
BUT NO COMMON ANCESTOR !
Structural Similarities
• The presence of structures that have a minimal purpose or no purpose at all are called Vestigial Structures
Evidence for Evolution: Embryos
• The early stages, or embryos, of many animals with backbones are very similar
Comparative Embryology
• Similarities in embryological development suggests a common ancestor and similar genetics.
http://bioweb.cs.earlham.edu/9-12/evolution/HTML/live.html
Evidence for Evolution: Geographic Distribution
• Animals found in the same geographic area tend to have multiple similarities
• Example: Marsupials in Australia
Chemical Similarities• The genetic code is the
same for ALL organisms.
• similar DNA sequences in all organisms.
• Greater similarities in DNA sequences implies greater evolutionary relatedness.
http://web.mit.edu/esgbio/www/dogma/images/code.gif
Evidence for Evolution: Molecular Biology
• All life on Earth shares at least SOME of the same DNA
• The more DNA you share, the more closely related on the evolutionary tree.
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