1. UNIT 8
Natural Selection

2. Artificial Selection
= process by which humans change a species by breeding it for certain traits
Dog breeds
Wild Cabbage
cabbage
broccoli
brussel sprouts
kohlrabi
kale

3. Darwin compared what he learned about breeding to his idea of adaptation
Said that in nature, environment creates selective pressure instead of humans in artificial selection

4. Natural Selection = mechanism by which environment is selective agent
Darwin used work of others to develop theory
Said adaptations arose over many generations
called process
“Decent with Modification”

5. Natural selection explains how evolution can occur
1.  All populations have genetic variation. That is, in any population there is an array of individuals that differ slightly from each other in genetic makeup. While this may be obvious in humans, it is also true in species whose members may appear identical, like bacteria.

6. 2. The environment presents challenges to successful reproduction
2. The environment presents challenges to successful reproduction. Naturally, an organism that does not survive to reproduce or whose offspring die before the offspring can reproduce does not pass its genes on to future generations

7. 3. Individuals tend to produce more offspring
than the environment can support. Thus individuals of a population often compete with one another to survive.

8. 4. Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring than those individuals less suited to the environment do.

9. “Descent with Modification”
= Over time, natural selection will result in species with adaptations that are well suited for survival

10. Fitness
= measure of ability to survive and produce more offspring relative to other members of a population

11. Before the industrial revolution, soot was rare in the English countryside. A light-colored moth was difficult to see against the clean bark.
Which moth would most likely be noticed by a hungry bird?

12. Natural selection acts on existing variation
Natural selection acts on phenotypes (not genetic material itself)
As environment changes, different traits will become beneficial.

13. Charles Darwin
“It’s not the strongest of the species that survive, nor the most intelligent, but the ones most responsive to change