PSYO 2160 Lecture Notes - Lecture 2: Natural Selection, Selective Breeding, Heritability
16 May 2018
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Natural selection
Artificial behavior
*When human chooses desired traits on different animals to be displayed, AND also for a
desired behavior. (Desired phenotype)
- Usually altering the phenotype might have an effect on the genotype.
- Humans are the selective agent.
Balyaev’s foxes
- A good example of artificial selection. And how altering the phenotype affects the
genotype.
- A selective study that choose wild foxes for breeding depending on the friendless towards
humans.
- It was noted that as the breading continued the new generation of foxes would display
different traits than the wild foxes.
- Such noticeable changes occurred in a just a couple fox generations (almost instantly in a
evolutionary point of view).
Natural selection
- Nature is the selective agent.
- Traits increases/decreases depending on the efficiency in the CURRENT environment.
(Those who survive, breed).
Basic principles
- Animals can produce more offspring than environment can support. (ex: polar bears; if a
bear has 2 cobs usually one of them dies)
- Competition among individuals of the same species for resources.
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- Only best adapted to environment survives to reproduce.
Natural Selection Requirements
- Variability in the trait.
*Mutation (in the sex cells), generic recombination (chromosomes exchanging genes), migration.
- Fitness consequences of the trait.
*The effect of a trait on an individual’s reproductive success: the mean number of
reproductively viable offspring and individual produces.
- Mode of inheritance for the trait.
*If a trait is not heritable it will wash away after that generation.
*Genetic transmission (heritability) & cultural transmission (watch and learn)
- Limited resources.
*No “end goal” (adaptations continue indefinitely to occur).
Heritability: measure of the production of variance in a trait that is due to genetic variance.
How to calculate heritability
1) Measure the average of a trait in every animal of the same age (X0).
2) Truncate the population variation in the trait and measure the average of this truncated
population with respect to the trait of interest (X1). Only allowing animals with an
specific score.
Selection differential; S = X1 – X0
3) Raise offspring of truncated population under identical conditions experienced by their
parents. Measuring trait at same age as parents. (X2).
Response of selection; R = X2 – X0
Heritability; h2 = R/S
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
*when human chooses desired traits on different animals to be displayed, and also for a desired behavior. (desired phenotype) Usually altering the phenotype might have an effect on the genotype. And how altering the phenotype affects the genotype. A selective study that choose wild foxes for breeding depending on the friendless towards humans. It was noted that as the breading continued the new generation of foxes would display different traits than the wild foxes. Such noticeable changes occurred in a just a couple fox generations (almost instantly in a evolutionary point of view). Traits increases/decreases depending on the efficiency in the current environment. (those who survive, breed). Animals can produce more offspring than environment can support. (ex: polar bears; if a bear has 2 cobs usually one of them dies) Competition among individuals of the same species for resources. Only best adapted to environment survives to reproduce. *mutation (in the sex cells), generic recombination (chromosomes exchanging genes), migration.
