1. KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

2. NGSSS
SC.912.L Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success. (MODERATE)

3. These observations led Darwin to write a book
Charles Darwin
Darwin set sail on the H.M.S. Beagle ( ) to survey the south seas (mainly South America and the Galapagos Islands) to collect plants and animals.
On the Galapagos Islands, Darwin observed species that lived no where else in the world.
These observations led Darwin to write a book

5. Giant Tortoises of the Galápagos Islands
Pinta
Tower
Pinta Island Intermediate shell
Marchena
James
Fernandina
Santa Cruz
Isabela
Santa Fe
Hood Island
Saddle-backed shell
Floreana
Hood
Isabela Island
Dome-shaped shell

7. “On the Origin of Species by Means of Natural Selection”
Charles Darwin
Wrote in 1859:
“On the Origin of Species by Means of Natural Selection”
Two main conclusions:
Species were not created in their present form, but evolved from ancestral species.
Proposed a mechanism for evolution: NATURAL SELECTION

8. Darwin’s Observations
Most species produce more offspring than can be supported by the environment
Environmental resources are limited
Most populations are stable in size
Individuals vary greatly in their characteristics (phenotypes)
Variation is heritable (genotypes)

9. moth (Biston betularia)
Natural Selection
Individuals with favorable traits are more likely to leave more offspring better suited for their environment
Example:
English peppered
moth (Biston betularia)

10. Click to view animation.
Example of directional selection animation.
Click to view animation.

11. Several key insights led to Darwin’s idea for natural selection.
Darwin noticed a lot of variation in domesticated plants and animals.
Artificial selection is the process by which humans select traits through breeding.
neck feathers
crop
tail feathers
Pigeon Traits
Selectively Bred Pigeons

12. Heritability is the ability of a trait to be passed down.
There is a struggle for survival due to overpopulation and limited resources.
Darwin proposed that adaptations arose over many generations.
Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals

13. Natural selection explains how evolution can occur.
There are four main principles to the theory of natural selection.
variation
overproduction
adaptation
descent with modification
DESCENT with MODIFICATION
ADAPTATION
OVERPRODUCTION
VARIATION

14. Variations: Differences in traits Come about by mutations in genes
Random
Occur in sex cells
Passed on to future generations

15. Over Production
Having many offspring increases the chance of survival but also results in competition for resources

16. Bird Beak Adaptations:

17. Adaptations: a certain variation suited to a particular environment that allow organisms to survive
Inuit people, who live in the extreme cold of the Arctic, have short, stout bodies that conserve heat.

18. Masai people, who live in the arid lands of eastern Africa, have tall, lean bodies that disperse heat well.

19. Descent with modification
Heritability of adaptations
More individuals will have the trait in every following generation
As long as the environmental conditions remain beneficial for the trait

20. Survival of the Fitness
Fitness is the measure of survival ability and ability to produce more offspring.
Does not mean the strongest!

21. Natural selection acts on existing variation.
Natural selection can act only on traits that already exist.
Structures take on new functions in addition to their original function.
wrist bone
five digits