Download Darwin`s Idea for Natural Selection

Darwin’s Idea for
Natural Selection
By Kristi Schramm
Open your books to page 378
 Read “Publication of ‘On the origin of
Species”
– Summarize in 3-4 sentences
 Read ‘Inherited Variation and Artificial
Selection’
– Summarize in 3-4 sentences
Darwin’s Influences
 Darwin studied many scientific theories of
his time
 Scientists that influenced Darwin’s later
theories include Hutton, Lyell, Lamarck and
Malthus
James Hutton and Charles Lyell
 Theory: The earth is many millions of
years old and that the same processes
that shaped the earth millions of years
ago are the same as today
 Made Darwin wonder:
– If the Earth could change over time, might
life change over time?
– This change would only be possible if the earth
was extremely old
Jean-Baptiste Lamarck
 Noticed that animals were “adapt” to their
environment
 Theory: Acquired Characteristics: the use or
disuse of a body part during it’s lifetime would
effect how traits were passed onto the
offspring.
 Made Darwin wonder:
– How did parents pass on their traits (inheritance)
– Why are organisms so well adapted to their
environment?
Thomas Malthus
 Observation: Babies are being born more
than people are dying.
 Theory: if the human population
continued to grow unchecked, eventually
there would not be enough food or living
space for everyone.
 Influenced Darwin: Organisms give birth
to many more offspring than can survive
and reproduce
Write these questions in the
Cornell Notes section (on the left)
 What did Darwin observe in the
Galapagos Islands?
 When did Darwin publish his ideas?
 What is Artificial Selection?
Darwin Presents His Case
 Darwin studies his
specimens from the
Galapagos
 The wrens, warblers, and
blackbirds he thought he
found were all actually
finches!
Darwin Presents His Case
 After 25 years of mulling over his theories,
Darwin receives a document from Alfred
Wallace summarizing the exact theory
Darwin came up with
Darwin Presents His Case
 Published his book in 1859
 Artificial Selection: Humans breed the
species with the most desired variations to
enhance the desired trait.
 Ex: Dog Breeding
Darwin’s Theory of Evolution by
Natural Selection
 Natural Selection is a process that allows
the evolution of species over time
 Darwin stated that three things must be true
for natural selection to occur:
– Struggle for Existence
– Survival of the Fittest
– Descent with modification
Struggle for Existence
 Based on Malthus’s work populations
Darwin’s theory states that there must be a
struggle for existence.
Not all offspring
can survive
because, there
is competition
for food, living
space and other
necessities of
life.
Survival of the Fittest
 Fitness= ability to survive and successfully
reproduce
 Higher fitness is a result of organisms
that have characteristics that help them
better survive in their environment.
(These characteristics are called
adaptations)
 Organisms with more beneficial
characteristics (phenotypes) will survive
better.
Descent with Modification
 Species today look different from
species long ago (fossil record)
 Natural selection will act on phenotypic
variations that allow organisms that occupy
different niches. By occupying a different
niche some of the variation is an adaptation
to one niche, while a different variation could
be an adaptation to another niche.
Variation in beak type made the birds more
suited for different niches.
Descent with Modification
 Implies that all species are related to one
another (common descent)
 Each living species has descended with
changes from other species
– How do you think these changes arose?
 Mutations
Evidence of Evolution
Darwin argued that life on earth has been
evolving for millions of years.
 The Fossil Record
 Geographic Distribution of Living Species
 Homologous Body Structures
 Similarities in Early Development
The Fossil Record
 Showed that:
– There have been countless species
that have lived on earth but no longer
live on earth today
– Layers of rocks with fossils (ancient
life) demonstrated that thousands, or
even millions of years were needed to
create this
The Fossil Record

Geographic Distribution of Living
Species
Capybara
Animals that are related
to each other showed
‘decent with
modification.’ Organisms
had modifications that
varied based on the
environment they lived in
Beaver
 Animals that were not
related each other
looked similar if they
were from similar
environments.
Muskrat
Geographic Distribution of Living
Species
Example: Based on what they look like:
Which two animals do you think are more
closely related to one another?
Desert Fox
Koala
Dingo
Geographic Distribution of Living Species
•Are not related to each other even though they look
more alike.
•Evolutionists say they look alike because they live in the
same kind of environment so over time they adapted in
similar ways
Desert Fox
Dingo
Homologous Structures
 Arms, wings, legs, and flippers all have
very similar bones
 Darwin believed this was evidence that all
species were original descended from one
common ancestor.
Similarities in Early Development
Looking at the
embryonic
development of
organisms Darwin
noticed some
similarities that
other scientists also
noticed.