1. Natural Selection
Darwin was sure that some mechanism of 
 inheritance was the key to evolution.
Darwin was interested in artificial selection - 
 (selecting for inheritable desirable traits to 
 change a species.)

2. Darwin thought that if people could alter the 
appearance and behaviour of species then why 
couldn’t nature do the same to wild 
populations.

3. Wild Sea Cabbage

5. The last piece he needed was to explain how 
nature chose individuals with desirable traits, 
like breeders do artificially.

6. The answer came in a paper Essay on the 
Principle of Population, by Thomas Malthus
Malthus believed that all organisms produce far 
more offspring than are able to survive.

7. Darwin realized that because of this there must be 
intense competition among individuals of the same 
species to survive. Under these conditions 
favourable variations would be preserved, 
unfavourable ones destroyed.

8. Darwin knew his ideas would be controversial, so instead 
of releasing it he continued to gather evidence and look for 
flaws in his reasoning.
In 1858 Darwin received a letter from Alfred Russell 
Wallace who independently arrived at the same conclusions 
about evolution as Darwin.
Darwin is credited with the ideas because of his 
supporting evidence.
When Darwin released his book, it sold out on the first 
day!

9. Darwin’s Theory of Evolution by Natural Selection
Observations
1. Individuals within a species vary in many ways.
2. Some of this variability can be inherited.
3. Every generation produces far more offspring than can 
 survive and pass on their variations.
4. Populations of species tend to remain stable in size.

10. Inferences
1. Members of the same species compete with 
 each other for survival
2. Individuals with more favourable variations 
 are more likely to survive and pass them on. 
 Survival is not random.
3. As these individuals contribute 
 proportionately more offspring to succeeding 
 generations, the favourable variations will 
 become more common. This is NATURAL 
 SELECTION.

11. Darwin provided detailed evidence and 
examples in support of his theory, which 
swayed many scientists at the time.

12. Natural Selection Ex Video.wmv

13. Unanswered Questions with Darwin’s Theory
For natural selection to result in a new species, large amounts of time are needed. No way of knowing the absolute age of earth. 
(Now we do!)
Limited fossil record, with many gaps and no transitional forms. (Now much greater, with transitional forms.)

14. ?

15. Unlike all living birds, Archaeopteryx had a full set of teeth, a rather flat sternum ("breastbone"), a long, bony tail, gastralia ("belly ribs"), and three claws on the wing which could have still been used to grasp prey (or maybe trees). However, its feathers, wings, furcula ("wishbone") and reduced fingers are all characteristics of modern birds.
archeopteryx

16. Puzzle of variation. Nobody knew the mechanism for the source of new variation (changes). How could small changes result in the formation of a wing or and eye? Darwin knew this was the weakness with is theory. (Gregor Mendel, Later - DNA)

19. Watch "Survival of the Wild Cats"
PBS - Evolution - The evolutionary arms 
race - Chapter 6

22. Attachments
Natural Selection Ex Video.wmv