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15.1 Theory of Natural Selection
Darwin's Theory of
Natural Selection
Section 15.1
Are these people different?
Darwin's Voyage
· HMS Beagle
England to South America
· read Lyell's Principles of
· ashore he found lots of
evidence supporting Lyell's
· variations and adaptations
Natural Variation
· physical differences among individuals
· 2 types
interspecific - members of different species
intraspecific - members of same species
· especially noticeable on Galapagos Islands
· noticed that animals seemed well suited for their
15.1 Theory of Natural Selection
1 What did Darwin notice about
organisms during his voyage?
Fossil and Geologic Evidence
· found fossil remains that were similar to modern
day organisms
suggested that modern organisms are related to
past life forms
ex. Glyptodon and armadillo
· found shells high in the Andes Mtn.
how did water-dependent organisms get there?
· experienced an earthquake that caused
underwater land to rise above sea level
· observations supported Lyell's theory
Earth older than 6,000 years
Earth gradually changing over time
· Could organisms be changing gradually, too?
Darwin Update
· 5 year journey
observations, collected specimen, experienced
geologic events
conclusion: change (evolution) happens
· How does evolution happen?
20 years gathering more information in England
studied work of farmers and breeders
Artificial Selection
· Darwin noticed variations in domesticated
plants and animals that were NOT present in
their wild relatives
· artificial selection - process of humans
changing a species by breeding it for certain
desirable traits
humans decided what is "useful"
dog breeds, race horses, seedless fruit
2 Which of the following did not suggest
to Darwin that change (evolution)
Charles Lyell's Principles of Geology
fossil evidence
changes in global climate
natural variations and adaptations
· Darwin started breeding pigeons
experimented with certain traits
· for artificial (or natural) selection to work, traits must
have heritability
traits can be passed from one generation to the next
· disproved that species had not changed since the
beginning of the Earth
Victoria Crowned Pigeon
15.1 Theory of Natural Selection
Natural Selection
· individuals that have
inherited beneficial
adaptations produce
more offspring on
average than do
other individuals
· environment decides
what is "useful"
selected traits gave
individuals advantages
in their environment
3 In natural selection, ____ determines
what is useful.
random mutation
your mom
the environment
Struggle for Survival
· Thomas Malthus
limited resources and
disease keep populations
in check
· Darwin reasoned the same
struggle took place in
"Descent with Modification"
· population - all the individuals of a species that
live in an area
· some individuals in a population had variations
that made them well suited to their environment
· adaptations arose over many
generations..."descent with modification"
organisms compete for
food, living space,
mates, etc.
Alfred Wallace
· English naturalist
· developed a theory similar
to Darwin's
· wrote a letter to Darwin to
complete the publish The
Origin of Species by Means
of Natural Selection (1859)
4 The notion that adaptations arise over
several generations is called
survival of the fittest
descent with modification
natural selection
adaptive radiation
15.1 Theory of Natural Selection
4 Principles of Natural Selection
· variation
heritable differences basis of natural selection
· overproduction
lots of offspring increases the chances that some will survive
creates competition for resources
· adaptation
certain variations allow an individual to survive better
"naturally selected" live longer and have more offspring that
share those adaptations
· descent with modification
over time, natural selection will results in species with
adaptations well suited for survival and reproduction
5 What are Darwin's 4 principles of natural
A organisms adapt to their environment
over-reproduction lead to competition
variation exists in populations
each generation is slightly different than
the one before it
Existing Variation
· acts on phenotypes NOT genotypes
· traits in a population become favorable for survival
b/c of a change in the environment
n.s. acts on traits that ALREADY exist
· new alleles occur through genetic mutation