DARWIN’S THEORYON THE ORIGIN OF

SPECIES

Natural Variation Even within a species individuals

vary from each other

Discussion QuestionThese are the same species of moth. The

two are naturally occurring variations.

Describe situations where the coloration would be an advantage for the moth.

How We Use Variation Artificial selection – nature provides

the variation and humans select the variations they find useful

Evolution by Natural Selection Natural Selection – the traits being

selected (which therefore increase over time) contribute to an organism’s fitness in its environment

Natural Selection The struggle

for existence Survival of the

fittest Descent with

modification

Struggle for Existence

Members of each species compete regularly to obtain food, living space, and other necessities of life

Run fast, behavioral tactics, camouflage

Survival of the Fittest Individuals better

designed for the environment where they live will survive and reproduce most successfully

Fitness is the result of successful adaptations

Survival of the Fittest Fitness – the ability to survive and

reproduce in a specific environment Adaptation – an inherited characteristic

that increases an organism’s chance of survival

Discussion Question Give three examples of animals

with designs that help their survival.

Tale of the Peacock Online Video Clip http://

www.pbs.org/wgbh/evolution/educators/course/session4/explain_a.html

Or: “Why Sex?” (PBS Evolution Series) minutes 17:00 – 28:00

KEY CONCEPTOver time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

Com

mon

Des

cent

Evidence for Evolution

1) Fossil record2) Animals with

similar selection pressures evolve similar features

3) Homologous structures

4) Similarities in early development

Genetic Toolkit Online Video Clip http://

www.pbs.org/wgbh/evolution/educators/course/session4/engage_a.html

(5 min)

similar habitats & similar structures

homologous structures

similarities in embryology