1. Darwin’s Observations
The Theory of Evolution by Natural Selection

2. The HMS Beagle
Charles Darwin embarked on the second voyage of the HMS Beagle on December 27,1831, on a survey expedition under the command of Captain Robert Fitzroy.
The main purpose of the expedition was to map out the southern coast of South America, and Darwin was on board as a geologist, to collect specimens.

3. The HMS Beagle (cont’d)
The journey was supposed to last 2 years, but the ship returned to England on October 2, 1836, almost 5 years after its departure.

4. What Darwin Saw
Similar flora & fauna (plants & animals) on the Galapagos as on mainland South America

5. What Darwin Saw (cont’d)
Many species of finches and mockingbirds

6. Other observations… The fossil record: Glyptodon (like the armadillo)
Megatherium (like the sloth)

7. Other observations (cont’d)
Comparative anatomy of animals:
Homologous features:

8. Other observations (cont’d)
Comparative anatomy of animals:
Analogous features:

9. Other observations (cont’d)
Comparative anatomy of animals:
Vestigial features:

10. Other observations (cont’d)
Investigated mechanisms of artificial selection (pigeon breeding, etc.)

11. Other observations (cont’d)
Thomas Malthus, Essay on the Principle of Population (1798)

12. The Theory of Evolution by Natural Selection
Observation 1: Individuals within a species vary in many ways.
Observation 2: Some of this variability can be inherited.
Observation 3: Every generation produces far more offspring that can survive and pass on their variations.
Observation 4: Populations of species tend to remain stable in size.

13. The Theory of Evolution by Natural Selection
Inference 1: Members of the same species compete with each other for survival.
Inference 2: Individuals with more favourable variations are more likely to survive and pass them on. Survival is not random.
Inference 3: As these individuals contribute proportionally more offspring to succeeding generations, the favourable variations will become more common. (This is natural selection.)