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Darwin, Evolution, and
Natural Selection
Scientific Theory
A. Social use of the word “theory”
1. Not the same as in science
2. Implies a hunch or a casual guess
B. Scientific Theory
1. Highly probable explanation based on vast collections of
scientific data
2. There are relatively few scientific theories
C. Examples of Scientific Theories
Cell Theory
Atomic Theory
Plate Tectonic Theory
Big Bang Theory
Theories of Evolution
Contributing Ideas….
Theories of Evolution
Hutton and Lyell (late 1700/early 1800’s)
- Fundamentalists said that the
Earth was around 6000 years
- Hutton and Lyell argued that
the Earth is many millions of
years and because
- Layers of rocks take time to
- Processes such as volcanoes and
earthquakes shaped the Earth
and still occur today.
Theories of Evolution
Malthus (1766-1834)
• Reasoned that if the
human population
continued to grow
unchecked, sooner or
later there would be
insufficient living space
and food for everyone
Theories of Evolution
A. Lamarck (1800)
1. Similar species descended from a common
ancestor – related to fossil record
2. Species change by ACQUIRING traits in their
lifetime by using their bodies in new ways
3. Acquired traits are NOT genes; they
are things that are learned
Theories of Evolution
Theories of Evolution
C. Charles Darwin (late 1800’s)
1. Background
a. medical and clergy student naturalist
b. HMS Beagle –goal was to survey the coast of S.
America (1831-1836) –Darwin collected biological &
geological specimens
c. Read Lyell’s Principles of Geology
which influenced his thinking as he
observed fossils—book proposed
the earth was millions of years old
Theories of Evolution
Darwin sailed on the Beagle from 1831-1836
Theories of Evolution
On the Galapagos Islands
a. Different islands seemed to have their own
slightly different varieties of animals
b. Finches had distinctive bills – 13 different species
c. Very similar – must have descended from a
common ancestor
d. Related this to artificial selection
Theories of Evolution
Theories of Evolution
Theories of Evolution
DARWIN ideas ~
Framework for Natural Selection (1840)
a. Individuals in a population show differences
b. Variations are inherited
c. Organisms have more offspring than can
survive on available resources
d. Variations that increase reproductive success
will have a greater chance of being passed on
than those that do not increase reproductive
Theories of Evolution
Wrote a book – Origin of Species (1859)
a. Compiled evidence for evolution and
explained how natural selection might provide a
mechanism for the origin of species
b. 1858: another naturalist (Alfred Wallace)
proposed a theory almost identical to Darwin’s
(saying species were modified by natural
selection)—Darwin published his book a year
later; evolution is only used once: on the last
“Natural selection and species
• Overtime, natural selection results in
changes in the inherited characteristics of a
• These changes increase a species fitness
(survival rate)
Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass those
advantages to their children
5. Species alive today are descended with
modifications from common ancestors