1. Natural Selection
March 3rd/4th, 2009

2. Evolution – or change over time – is the process by which modern organisms have descended from ancient organisms.

3. Before Natural Selection…
Artificial Selection - human intervention in animal or plant reproduction to ensure that certain desirable traits are represented in successive generations.
In artificial selection, nature provides the variation, and humans select those variations that they find useful.

4. The different breeds of domestic dogs are products of artificial selection.

5. Evolution by Natural Selection
Adaptations are those inherited characteristics that enhance an organism’s ability to survive and reproduce in a particular environment.

7. Natural Selection – also called “survival of the fittest” – is the unequal survival and reproduction that results from the presence or absence of particular traits.

8. Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ “fitness” in its environment.

9. Polar Bear Adaptations

10. Story of the Peppered Moth
Before the industrial revolution, peppered moths strived because they were able to blend in with the light-colored bark on the trees.
Dark-colored moths were easy prey for predators.

11. During the industrial revolution, soot from factories covered oak trees, turning them dirty and dark.
The population of light colored moths decreased and the population of dark colored moths flourished.

12. The Peppered Moth

13. 2 1 3

14. Evolving Ideas: How Does Evolution Really Work?
(Hyperlinked Video)

15. In order for natural selection to occur…
Variation – individuals in a population must vary from one another.
Inheritance – these variations must be inheritable.
Over production of offspring – more offspring must be produced than can survive.
Selection – individuals with advantageous variants reproduce more than others.
Time – successful variations accumulate over many generations

16. Reflection
How is artificial selection different from natural selection?
True or false. Evolution is brought about by need or want.
What did Darwin mean when he described certain organisms as “more fit” than others?
What five conditions must be present in order for natural selection to occur?

17. Natural Selection’s Key Ideas
All individuals in a population are different from each other and thus reproduce unequally. Diversity is key to evolution. There needs to be variation!!!
Natural selection is situational- occurs as organisms interact with their specific environment. A trait may be helpful in one environment and unhelpful or neutral in another.
Organisms with the best adaptations will survive and reproduce the best.
These organisms will pass on their adaptations to their offspring.