UNIT 8 Natural Selection

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

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

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”

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.

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  

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

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.

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

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

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?

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

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