Darwin, Evolution, and Natural...

Darwin, Evolution, and Darwin, Evolution, and Darwin, Evolution, and Darwin, Evolution, and Natural SelectionNatural SelectionNatural SelectionNatural Selection

Scientific TheoryScientific TheoryScientific TheoryScientific 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 Theory1. Highly probable explanation based on vast collections of

scientific data

2. There are relatively few scientific theories

C. Examples of Scientific Theories1. Cell Theory

2. Atomic Theory

3. Plate Tectonic Theory

4. 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

old.

- Hutton and Lyell argued that

the Earth is many millions of

years and because

- Layers of rocks take time to

form

- Processes such as volcanoes and

earthquakes shaped the Earth

and still occur today.

Theories of EvolutionTheories of EvolutionTheories of EvolutionTheories 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


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


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


Darwin sailed on the Beagle from 1831-1836


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


Galapagos

Turtles


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

success


DARWIN~

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. 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 page!

““““Natural selection and species Natural selection and species Natural selection and species Natural selection and species fitnessfitnessfitnessfitness””””

• Overtime, natural selection results in

changes in the inherited characteristics of a

population.

• 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

Darwin, Evolution, and Natural...

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