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Lecture 10

BIOL 215 Lecture Notes - Lecture 10: Guppy, Disruptive Selection, Directional Selection

Biology (Sci)
Course Code
BIOL 215
Neil Price

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BIOL215 Lecture 10 Notes
Overview on selection acts on populations in four ways:
Stabilizing selection
Directional selection
Disruptive selection
Sexual selection
Selection acts on variation
Selection constrained by genetic and developmental pathways. This means that not every single
mutation that happens on the level of DNA or not every tinkering occurring in the environment
shows up on the phenotype. If it did, it would be disastrous for the individual. Individuals have a
way of buffering to protect themselves
Is evolution survival of the fittest as discussed in class:
Survival of the most adaptable
Coined by Herbert Spencer, was used by Wallace, and by Darwin in later editions of "The Origin of
Tautological- Darwin preferred "struggle for reproduction"
Natural selection is the umbrella term for a range of evolutionary processes, the outcome of
which is differential survival and reproduction
"Struggle for existence or survival of the fittest" is only one part of natural selection:
Biotic: being able to compete with your neighboring individuals in the same populations,
individuals of a different species
Abiotic: being able to survive in your conditions
The relative reproductive success of individuals, within a population, in leaving offspring for the
next generation
Fitness of phenotype (individuals) vs genotype (alleles)
Need both survival and reproductive success
Genotype vs. Phenotype
Natural selection directly acts on the phenotype (what it looks like on the outside)
Selection only indirectly affects the genotype
Natural selection combined (view of Darwin for species we see today):
Vastness of geologic time
Uniformitarianism (gradual change in the environment)
Continuously limited resources
Non-random survival
Stabilizing selection: when you are stabilize around the mean, when the mean is particularly well
adapted to the environment and individuals on either side of the mean is selected out (i.e. optimal
temperature for survival)
Directional selection: when the mean is favored and shifted over to one direction with each passing
generation (height in humans)
Disruptive selection: when there are two peaks that are selected for; want two types of individuals in
a particular population. It usually occurs when environments change very quickly
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