1. Natural Selection
Notes

2. *Population: breeding group; only members of same species can reproduce with each other
*DARWIN:
*EVOLUTION: descent with modification
***change over time
*compared anatomy of different species; studied in Galapagos and other areas for over 20 years
*believed life forms can and do change

3. *2 reasons for his ideas:
In nature, commonly an overproduction of offspring
Ex. One mouse  6 offspring WHAT IF ALL LIVED?
1. Must be a struggle for existence among individuals
i.e. Competition for ????
Selective breeding: individuals have variations of traits
Ex. Farmers breed only strong plants, animals

4. *Individuals w/ variations for traits adaptive to environment have greater chance for surviving; these reproduce and have offspring with similar traits
*Thus, adaptations are passed on
*Alfred Wallace– another scientist that came to same conclusions; did not know Darwin
*Darwin couldn’t fully explain how it all worked– didn’t know about genes (duplications, mutations, etc) or meiosis

5. *Natural Selection: best adapted individuals in population survive and produce offspring (which are adapted as well)
*Affected by interaction of organisms and environment
(Suitable variations to environment are passed on from one generation to the next)

6. *Theory of Natural Selection:
In nature, tendency toward overproduction
Not all offspring that are produced will survive
Variations exist in any population
Variations are inherited
Those individuals with variations that are suitable for their environment will live longer & have more offspring on average than will individuals not having those variations
Resulting population as a whole will change as it becomes better adapted to environment

7. *Population Genetics:
*genotype of individual remains constant but, over time, genes within population may change
*new phenotypes are then produced
*Gene pool:
entire collection of genes among population
*Population genetics:
Study of gene pools

8. *Allele frequency: % of an allele in population
Ex. Insects: A= greenish brown
a= dark brown
If 50% A, 50% a, the frequency of A is 0.5 and frequency of a is 0.5
Thus, 25% are AA, 50% Aa, and 25% aa
If A = dominant, 75% are greenish brown
*What if bark color was dark brown? What would happen? Which would survive better?

9. Lab Activity Tomorrow!