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Natural Selection--process by which adaptation occurs
3 mechanisms (overhead 23.11)
a) stabilizing--intermediate phenotypes are chosen, extremes eliminated
b) directional--shifts characteristic in 1 direction
c) diversifying--environmental conditions varied to favor both extremes
How it works-Depends on population size
Struggle for survival of the fittest (ability to survive and reproduce); they have certain characteristics (the tallest
giraffe gets the best leaves!)
The struggle leads to change in species to better suit environment (taller giraffes in poplulation.)
Artificial Selection--man makes the selection--Dogs w/ big ears, Cats w/ no fur
Variance--range of phenotypes for a trait (4 to 6 ft tall)
Heritability--measure of genetic contribution to phenotype of organism. How similar are progeny to parents?
EvolveIt Exercise--Look at changes in environment and effects on beak size and survival of finches on 2
islands--Darwin and Wallace.
Go to same website as we used for fly lab, choose Evolution lab --need user id (computer #) and password
then go to change inputs and select parameter to be altered as assigned (beak, variance, heritability, clutch
size, island size, precipitation)& select 300 yr & wait for initial graph computed (beak size vs. year), will tell you
mode of natural selection & also click on population tab to see if changes in environment lead to extinction.