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Chapter 1

PSYCH 3F03 Chapter Notes - Chapter 1: Overproduction, Mutation, Assistive Technology

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David Feinberg

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Understanding Natural Selection
- Natural Selection: a non-random difference in reproductive output among
replicating entities, often due indirectly to differences in survival in a
particular environment, leading to an increase in the proportion of beneficial,
heritable characteristics within a population from one generation to the next
- Populations have the capacity to increase in numbers exponentially, 2n
- Overproduction = superfecundity
- Why don’t populations expand indefinitely? Most offspring that are produced
do not survive to produce offspring of their own. Most populations stay
relatively stable
- Struggle for existence: only a tiny fraction of individuals will reproduce,
species vs. same species, species vs. different species, species vs.
- Any variation that is not inherited is unimportant to us; we are more similar
to our siblings and parents than those we’re not related to
- Individuals which possess a trait which makes them better suited to an
environment will leave more offspring; not passes randomly as those who
possess that trait are more likely to survive
- Two step process: first, the origin of variation by random mutation, and
second, the non-random sorting of variation due to its effects on survival and
- Darwinian Fitness: a measure of the total reproductive output of an organism
with a particular genotype
- Traits are only considered important if they influence reproduction
- Organisms do not evolve, populations evolve
- Evolution is a two step process: first, the generation of new variation by
mutation and recombination, second determines which randomly generated
variants will persist into the next generation
- Small advantages can create beneficial mutation to increase proportion over
many generations
- Mutation becomes fixed: only one to survive, all other mutations filed to be
passed on
- Beneficial mutations arise continually and accumulate in populations over
- Mutations are the source of new variation, natural selection itself does not
create new traits, it only changes the proportion
- Mutation is random with respect to fitness, natural selection is non-random
with respect to fitness
- Mutations can be neutral, deleterious and beneficial, beneficial mutations are
rare and minor but can accumulate
- Organisms don’t change, populations change through the proportion of
beneficial traits
- Change in environment causes change in type of mutation
- Adaptation isn’t optimal characteristics by limitations and trade-offs in
history, genes and development
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