•Dark-colored moths camouflaged (to hide) from predators in the polluted environment.

•Some light-colored moths may have migrated in from other areas.

•Some light-colored moths may have other adaptations that are more important than color for survival.

•Some light-colored moths may taste bad.

•Some light-colored moths rested in areas other than the bark.

• The tree trunks were covered with lichens, so light colored moths camouflaged better and survive.

• The species could become extinct.

• The species does not evolve.

What is the Source of Variation?

Mutations

Change in DNA

Random mistakes during replication

Mutagens•Radiation (Ultraviolet radiation, X-Rays•Chemicals

Body cells

Sex cells

Causes

Pass to offspring

Harmful99.999…%

Beneficial0.000…%

Organism better adapted to environment

More chances of surviving

New beneficial changes

New species

Random recombination of

genes

New combination

of genes

Sexual reproduction

Crossing overExchange of DNA segments between non-sister chromatids

Meiosis (prophase I)

Independent assortment of chromosomes

Meiosis (anaphase I)

+

Fertilization Combination of genesfrom two different individuals

Egg (female)

Sperm (male)

+ Zygote

gametes

gametes

• Mutations change DNA, resulting in new traits. • Sexual reproduction involves union of DNA from two parents, resulting in offspring different from either parent.

• The environment changed and the wooly mammoth could no longer adapt.

•Increase of predators

• Increase competition with other plant-eaters.

•Overhunting by humans

•Bears and canines share common ancestors.

•Miacis is an ancestor of bears and canines

•Bears are more closely related to raccoons than to the domestic dog.

The two animals area adapted to different environments.

GENETIC VARIATIONNot all of the bacteria were identical. They had genetic variation. Some bacteria have genes to make thin cell walls and some have genes to make thick cell walls.

SURVIVAL OF THE FITTESTThose bacteria with thick cell walls were better adapted to survive in the presence of the chemicals. This is known as survival of the fittest.

DIFFERENTIAL REPRODUCTION These bacteria which survived, they reproduced and passed on the favorable genes – to have thick cell walls - to the next generation.