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BI 1: Natural Selection

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Kimberly Christian

on 14 September 2017

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Transcript of BI 1: Natural Selection

Natural Selection
goal of life = survive to reproduce and pass on your genes
ADAPTATIONS allow organisms to survive and reproduce.

Individuals without adaptations cannot compete to survive and reproduce.
After many generations
environment can only act in the present
evolution does not prepare species for the future environment
# individuals with adaptations
# individuals without adaptations
Descent with Modification
Darwin proposed:
all organisms descended from a common ancestor in the past
descendants lived in different habitats over millions of years
descendants accumulated unique adaptations for their specific way of life
so, descent with modification has led to tremendous diversity of life today
= process by which individuals with certain characteristics survive and reproduce at a higher rate than other individuals
Six Principles of Natural Selection
populations have the potential to produce more offspring than the environment can support
availability of food, water, shelter, etc. is insufficient to meet the needs of the population
organisms struggle to obtain a share of the limited resources
differences between individuals are based in genetics and can be
passed to offspring
some organisms have variations that make them more successful at competing for resources
individuals with adaptations reproduce more frequently than individuals without adaptations
Modes of Natural Selection
natural selection typically acts on a population and its phenotypic distributions in one of three ways:
disruptive selection
stabilizing selection
directional selection
environment selects against the mean and favors the extreme phenotypes
environment selects against extremes and favors the mean phenotype
environment selects against one extreme and favors the opposite extreme
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