1. Evolutionary Theory

2. Some Definitions to Remember…
Evolution is the process by which species change over time
A theory is a broad explanation that has been scientifically tested and supported
The Theory of Evolution explains the evidence suggesting that life on Earth has changed
The Theory of Evolution was proposed by Charles Darwin

3. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
The Voyage of the Beagle
5 year trip around the world
He collected & observed natural objects from each place that he visited

4. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
The Voyage of the Beagle
5 year trip around the world
He collected & observed natural objects from each place that he visited
Fossils of extinct armadillos were similar but not identical to living armadillos in the area

5. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
The Voyage of the Beagle
5 year trip around the world
He collected & observed natural objects from each place that he visited
Fossils of extinct armadillos were similar but not identical to living armadillos in the area
Finches from the Galapagos Islands were similar, except for their beaks

6. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
The Voyage of the Beagle
5 year trip around the world
He collected & observed natural objects from each place that he visited
Fossils of extinct armadillos were similar but not identical to living armadillos in the area
Finches from the Galapagos Islands were similar, except for their beaks
He noticed that all organisms were well suited to their environments and diets

7. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
Years of Reflection
After returning from his voyage on the Beagle, Darwin (27 at the time) studied his data for many years.
He did not report his data until much later

8. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
Breeding and Selection
Darwin noticed that humans take advantage of the variations among organisms of the same species as they breed them
In other words, humans choose to breed the organisms with the “best” traits
Darwin called this artificial selection
What examples of artificial selection can you think of?

9. The Evolutionary Theory was Influenced by Darwin’s Life Experiences:
Examples of Artificial Selection
Horses are bred for strength, speed, beauty, and size
Flowers are often bred for brighter and more varied colors.
Corn is bred to have many full kernels in straight rows and to taste great.
Strawberries are bred for color, size, and durability. Wild berries taste better.

10. The Evolutionary Theory was Influenced by Darwin’s Peers:
Lamarck
First prominent scientist to defend the idea that species could change
Thought that species passed on acquired traits due to use and/or disuse

11. The Evolutionary Theory was Influenced by Darwin’s Peers:
Malthus
Economist
Stated that the human population is limited by resources
Darwin applied this idea to all populations

12. The Evolutionary Theory was Influenced by Darwin’s Peers:
Cuvier
Argued that fossils in rock layers showed differences in species over time
Said that species from the past differed from those in the present

13. The Evolutionary Theory was Influenced by Darwin’s Peers:
4. Lyell
His research pointed out that the Earth was old enough for species to have evolved gradually

14. Evolution by Natural Selection
Darwin’s theory predicts that over time, the number of individuals that carry advantageous traits will increase in a population due to nature SELECTING FOR those traits.

15. Aspects of Darwin’s Theory:
Overproduction: Every population produces more offspring than survive
Variation: There is variation in every population (some inherited, some random)
Selection: In a given environment, some traits give an organism a better chance at survival, so that organism lives and reproduces
Adaptation: Traits that improve survival become more common in the population

16. Publication of his Theory
After many years, Darwin wrote an outline of his theory of evolution by natural selection
He didn’t publish it because he was afraid that his ideas would be controversial
UNTIL…

17. Publication of his Theory
Darwin received a letter from Alfred Wallace
In the letter, Wallace wanted Darwin’s opinion on his new theory… one JUST like his!
This prompted Darwin to publish a book of his ideas
In his book, Darwin:
Explained his Theory
Offered evidence that suggested that evolution had occurred