1. Theory of Natural Selection
Chapter 15
Section 1

2. Learning Targets I can… Explain the biological definition of evolution
Discuss Darwin’s principle of survival of the fittest and explain what Darwin meant by natural selection

3. Developing the Theory Charles Darwin – “The Father of Evolution”
Darwin boarded the HMS Beagle in 1831 to survey the coast of South America
Darwin was a naturalist and companion to the captain
His job was to collect biological and geological specimens during the ship’s travels

4. Developing the Theory
In 1835 the HMS Beagle arrived at the Galapagos Islands
Darwin began to collect mockingbirds, finches, and other animals on the four islands he visited
Noticed that different islands seemed to have their own, slightly different varieties of animals.

5. Developing the Theory

6. Developing the Theory
After Darwin returned to England, he reconsidered his observations
He determined that almost every specimen brought from the islands was new to European scientists
The specimens did resemble specimens on the main land of South America, though they were not identical

7. Developing the Theory

8. Developing the Theory
Darwin hypothesized that new species could appear gradually through small changes in ancestral species, but wasn’t sure how this could work
- So, he turned to
animal breeders
to get a better
understanding

9. Developing the Theory
Darwin learned that breeders use Artificial Selection
Artificial Selection is where a breeder can promote traits that are beneficial to the species or work to remove traits that are not beneficial
Can also result in developing new breeds of dogs or new strains of crop plants, etc.

10. Developing the Theory
While thinking of Artificial Selection , Darwin read an essay by the economist Thomas Malthus
The essay suggested that the human population, if unchecked, eventually would outgrow its food supply, leading to a competitive struggle for existence
Darwin realized that Malthus’ ideas could be applied to the natural world.

11. The Theory of Natural Selection
Darwin then proposed his Theory of Natural Selection, which had 4 principles:
Individuals in a population show variations among others of the same species
Example: No
single zebra has
the same stripes
as another

12. Theory of Natural Selection
Variations are inherited
Ex: Children look similar to parents
Animals have more young than can survive on available resources
Ex: Cardinals lay 9 eggs (on avg.) per summer. If each cardinal lived only one year, in seven years there would be a million cardinals if all offspring survived.

13. Theory of Natural Selection
Variations that increase reproductive success will be more common in the next generation
- ex: If having a fan-shaped tail increases reproductive success of pigeons, then more pigeons in the next generation will have fan-shaped tails.

14. The Origin of Species
It is believed that Darwin’s theory originated near 1840
Soon after he began writing a multi-volume book compiling evidence for evolution and explaining how natural selection provides a mechanism for the origin of species

15. The Origin of Species
Darwin eventually published his book “ On the Origin of Species by Means of Natural Selection”
In his book, Darwin used the term evolution only on the last page.
Today, biologists use the term evolution to define cumulative changes in groups of organisms through time

16. Evolution
Darwin’s theory of natural selection is not synonymous with evolution
It is a means of explaining how evolution works

17. Explore the Galapagos
Go to the website
Complete the questions on the packet for #1 – 10.
Then complete the diagram question on the back of the packet