Darwin, Evolution, and Natural Selection

Scientific TheoryA. Social use of the word “theory”

1. Not the same as in science2. Implies a hunch or a casual guess

B. Scientific Theory1. Highly probable explanation based on vast collections of scientific

data2. There are relatively few scientific theories

C. Examples of Scientific Theories1. Cell Theory2. Atomic Theory3. Plate Tectonic Theory4. Big Bang Theory

Theories of EvolutionA. Lamarck (1800)

1. Similar species descended from a common ancestor – related to fossil record

2. Species change by ACQUIRING traits in their lifetime

3. Acquired traits are NOT genes; they are things that are learned

Theories of Evolution

Theories of EvolutionB. Alfred Wallace (late 1800’s)

1. species were modified by natural selection

Theories of EvolutionC. Charles Darwin (late 1800’s)

1. Backgrounda. medical and clergy student naturalistb. 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

Theories of Evolution2. On the Galapagos Islands

a. Different islands seemed to have their own slightly different varieties of animals

b. Finches had distinctive bills – 13 different speciesc. Very similar – must have descended from a

common ancestord. Related this to artificial selection

Theories of Evolution

Theories of Evolution3. Framework for Natural Selection (1840)

a. Individuals in a population show differences

b. Variations are inheritedc. Organisms have more offspring than can

survive on available resourcesd. Variations that increase reproductive success

will have a greater chance of being passed on than those that do not increase reproductive success

Theories of Evolution

Galapagos Turtle

Theories of Evolution4. 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—Darwin published his book a year later; evolution is only used once: on the last page!

Summary• Over time, natural selection results in

changes in the inherited characteristics of a population.

• These changes increase a species fitness (survival rate)