Chapter 16: Darwin’s Theory of
Evolution
Darwin’s Voyage of Discovery
Darwin’s Journey
• Charles Darwin
– British scientist and naturalist
– 5 year journey around the world on the HMS
Beagle
– Hit Australia, Africa, and South America
– Collected plants and animals
– This journey was the foundation for his theory of
evolution
Observations aboard the Beagle
• 1. Species vary globally
– Ex: Emus, Rheas, and Ostriches
– Flightless birds found on 3 continents
– Similar habitats but different animals
• 2. Species vary locally
– Ex: Tortoises of the Galapagos Islands
– Different animals in the same environment
• 3. Species vary over time
– Ex: Fossils of organisms
– Some looked similar to animals today; others didn’t
Chapter 16: Darwin’s Theory of
Evolution
Ideas that shaped Darwin’s Thinking
Role of Geology
• People believed Earth was not old and not changing
• Geology was emerging and showing something else
• James Hutton (1726-1797)
– Geological processes shape the land
– Forces push mountains up
– Deep time: Earth’s history so long we can’t imagine it
• Charles Lyell (1797-1875)
– Principles of Geology
• Laws of nature don’t change over time
• Changes in landscape take millions of years
Lamarck’s Evolutionary Hypothesis
• Jean Baptiste Lamarck (1744-1829)
– Created the first theory of evolution
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All organisms born with desire to become better
Organisms could change bodies to adapt to environment
Acquired characteristics: Traits that change during organism’s life
Acquired traits can be passed onto offspring
– Although most ideas were wrong, he was on the right track
– Made the connection between an organism’s body and its
environment
Role of Economics
• Thomas Malthus (1766-1834)
– English economist
– Ideas designed for human population but can be used for
all organisms
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People born quicker than people dying
This leads to overcrowding
Overcrowding lead to conditions that slow growth
Important that only a few survive but which ones
Artificial Selection
• People chose best traits within organisms and breed
them
• Object is to create bigger and better products
• Variation can occur in the wild as well as domestic
• Ex:
Chapter 16: Darwin’s Theory of
Evolution
Darwin Presents his Case
Evolution by Natural Selection
• 1. Struggle for Existence
– Members of population compete for food, water, and
living space
– Those that don’t get enough won’t survive
• 2. Variation and Adaptation
– Variation
• Heritable traits: traits passed onto offspring
• Heritable traits make survival easier
– Adaptation
• Any heritable trait that allows an organism to survive in the
environment
Evolution by Natural Selection
• 3. Survival of the Fittest
– Differences in adaptations affect fitness
– Fitness: How well an organism and survive and reproduce
in its environment
– Individuals with these adaptations will survive more than
those without the adaptations
Evolution by Natural Selection
• 4. Natural Selection
– Organisms with the best traits to match their environment
will survive
– 3 conditions needed for it to exist
• 1. More individuals being born than dying
• 2. Heritable traits in the population (variation)
• 3. Some individuals have traits that all them a better chance to
survive
– If environment changes, the population will change
Common Descent
• Every organism today descended from parents who
survived and reproduced
• Descent with modification
– Older species evolve into new species
– Deep time allows Darwin to validate natural selection
– Fossil Record is evidence of descent with modification
• Common Descent
– All organisms share an ancient common ancestor
Chapter 16: Darwin’s Theory of
Evolution
Evidence of Evolution
Evidence of Evolution
• Biogeography
– Study of where organisms live and where ancestors lived
– 2 patterns arose:
• 1. Closely related organisms that lived in different environments
showed many differences
– Each environment is different and forces organisms to adapt
differently
• 2. Distantly related organisms that live in similar environments are
often similar
– Organisms will have similar adaptions if they are in similar
environments
Evidence of Evolution
• Body Structures
– Homologous Structures
• Similar structures found in different organisms allow us to say they
have been inherited from a common ancestor
Evidence of Evolution
Analogous Structures
• Show us that organisms that have structures with similar functions
but different structures are not as closely related as thought to be
• Ex: different wings in flying animals
Evidence of Evolution
Vestigial Structures
• Structure in an organism that was once useful to a previous
ancestor but no longer has a function in organism
• Ex: Hip bone in whales and dolphins
Evidence to Evolution
• Embryology
– At an embryonic stage, all organisms look and develop in
the same way