1. The Evolution of Evolutionary Theory

2. Theory vs Fact
Scientific Theory: “A well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment.“

3. Theory vs Fact
Scientific Fact: Scientists most often use the word "fact" to describe an observation. But scientists can also use fact to mean something that has been tested or observed so many times that there is no longer a compelling reason to keep testing or looking for examples. 

4. Theory? Fact? Both?
"Darwin continually emphasized the difference between his two great and separate accomplishments: establishing the fact of evolution, and proposing a theory—natural selection—to explain the mechanism of evolution.“
Scientists continue to argue about particular explanations or mechanisms at work in specific instances of evolution, but the fact that evolution has occurred and is still occurring is undisputed.

5. James Hutton (1726-1797) and Charles Lyell (1797-1875)
Studied the forces of wind, water, earthquakes and volcanoes.
They concluded the earth is very old and has changed slowly over time due to natural processes

6. Erasmus Darwin( )
Suggested that competition between individuals could lead to changes in species.
He was also Charles Darwin’s grandfather.

7. Jean Baptiste Lamarck (1744-1829)
The first scientist to propose a system of evolution.
Noticed that fossils became more complex in earlier rock strata, therefore a drive towards complexity.
Each species came from less complex ones

8. Lamarck (continued) Believed that evolution is based on 2 principles:
1. Law of use and disuse
The more an animal uses a certain part of the body, the stronger and better developed it becomes
2. Inheritance of acquired characteristics Characteristics an organism developed through use and disuse could be passed on to its offspring

9. Thomas Malthus ( )
Observed that human populations cannot keep growing indefinitely.
If the birth rate continued to exceed the death rate, eventually humans would run out of space and food.
Famine, disease and war prevented endless population growth.

10. Charles Darwin ( )
Formulated a theory of evolution by natural selection based on observations made during his voyage on the Beagle, and of selective breeding of farm animals, plants and pets.
He drafted manuscripts outlining his theory in the 1840s but hesitated to release them to the public.
His most famous work On the Origin of Species by Means of Natural Selection was published in 1859.

11. Darwin’s Theory:
Overproduction: more offspring are produced by an organism than can possibly survive.
Competition: high birth rates cause a shortage of life’s necessities leading to competition between organisms.
Variation: each individual differs from all other members of its species; some differ more than others.

12. Darwin’s Theory (continued)
Adaptation: allows organisms to become better suited to their environment.
Natural Selection: the most fit (best adapted) organisms survive and reproduce.
Speciation: formation of new species from ancestral species by means of natural selection.

15. Alfred Russell Wallace (1823-1913)
Proposed a theory of evolution by natural selection similar to that of Darwin.
He wrote a paper and sent it to Darwin to review. This paper spurred Darwin on to finally agree to the release of his theory.
In 1858, Charles Lyell presented Darwin’s 1844 essay and Wallace’s paper to the public.

16. New Theorists!