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Evolution:
Why Are There So Many
Living Things?
Where Did the Idea of Evolution
Come From?
• Middle Ages:
– “Ladder of Life”
• Complex organisms
found at highest rungs
• Less complex at lower
rungs
• 1800’s
– Georges Cuvier
brought study of
fossils to the level of
science.
Where Did the Idea of Evolution
Come From?
• Charles Lyell
– Proposed theory of uniformitarianism.
• Jean-Baptiste Lamarck
– Published theory of the inheritance of
acquired characteristics.
Charles Darwin
• Loved nature
• Studied medicine
– Struggled with the
inhumane operating
procedures
• Switched to religion
• Offered position as
naturalist on British
survey ship, The
Beagle.
Voyage around the World
• Studied animals and
fauna.
• Noticed South
American fossils
differed from
contemporaries.
• Collected data for 27
years to support his
mechanism for
evolution.
Fathers of Evolution
• Alfred Wallace studied in Brazil and East
Indies.
• Developed mechanism of evolution
independently of Darwin.
• Sent a copy of it to Darwin.
– Contained same conclusions as Darwin
• Both presented their data at Linnaean
Society of London in July 1858.
How Did Darwin Account for
Species?
• In Origin of Species,
he developed two
main concepts
– Evidence that
evolutions has
occurred.
– Mechanism for
evolution :natural
selection.
Major points of Darwin’s theories of
evolution and natural selection
• First observation:
– Populations have
the potential to
increase
exponentially.
• Based on thoughts
by Thomas Malthus
Major points of Darwin’s theories of
evolution and natural selection
• Second observation:
– Populations are fairly
constant in size.
Major points of Darwin’s theories of
evolution and natural selection
• Third observation:
– Natural resources are limited.
• Limited amount of space, nutrients, shelter
• Results in competition for resources to
survive.
Major points of Darwin’s theories of
evolution and natural selection
• Deduction one:
– Only some organisms
survive. There is a
struggle for existence
among individuals in a
population.
• Organisms posses
characteristics that
enhance survival
– Called adaptations.
Three Types of Adaptations
• Morphological-anatomical: modifications
in form and structure that enhance
survival.
• Biochemical-physiological: modifications
in the production and use of chemicals by
organisms.
• Behavioral Adaptations: Modifications in
animal interactions with others and
environment.
Major points of Darwin’s theories of
evolution and natural selection
• Fourth observation:
– There is variation within individuals of a population
and variations are inherited.
Major points of Darwin’s theories of
evolution and natural selection
• Deduction two:
– Individuals with
favorable variations
are more likely to
survive and reproduce.
• Natural Selection:
– “preservation of
favorable variations
and the rejection of
injurious variations”
Major points of Darwin’s theories of
evolution and natural selection
• Deduction three:
– Accumulation of
inheritable variation
over many generations
is evolution.
• If changes within a
species become great
enough, a new
species can result.
What is a species?
• Species are considered extinct if they do not
interbreed in nature.
– Implies offspring must also be able to reproduce.
Evidence supporting Theory of
Evolution
• Selective breeding
practices used by
farmers result in:
– “improved”
domesticated plants
and animals.
• Darwin wondered if
nature could do the
same.
Evidence supporting theory of
evolution
• Fossil record
– Comparing fossils from ancestors with today’s
species demonstrates species have evolved.
Evidence supporting theory of
evolution
• Homologous
structures
– Structures dissimilar in
form and function.
• but share underlying
structural similarities
– Similarity due to a
common ancestor?