Natural Selection Fitness individuals ability to a survive

Natural Selection : Fitness = individual’s ability to… a) survive long enough to reproduce b) find a mate c) produce live offspring Natural Selection = survival of the fittest

For Natural Selection to work: 1) more offspring born than can live in area 2) genetic variation (not clones) 3) some alleles better than others

Artificial Selection Humans select which individuals survive or reproduce

Sexual Selection Natural selection for traits that help get mates Physical Traits Behavioral Traits

Bower Birds

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The Effects of Natural Selection is a process It changes the gene pool of a population It results in a change in allele frequency

Alleles that improve fitness become more common Alleles that decrease fitness become less common, …. may be eliminated from population

Some traits only have 2 alleles Example: Peppered Moth

Natural Selection of monogenic Traits Can be shown by a line graph Y-axis = # of individuals X-axis = time

Natural Selection of Polygenic Traits Shown by before and after histograms Traits show a range of phenotypes

3 Ways Natural Selection Can Go 1) It can select FOR one extreme 2) It can select For being average 3) It can select AGAINST being average

Directional Selection

1. Directional Selection Select for one extreme = directional Graph moves in one direction over time

Directional Selection example 1976 All Birds N = 751 1978 Survivors N = 90 Figure 1: Histogram of distribution of beak depth of medium ground finches (Geospiza fortis) on Daphne Major, before and after the drought of 1977 (Grant 1986). Reprinted by permission of Princeton University Press.