Mutation – the origin of new genetic variation
Genetic drift- changes due to chance, specifically founder effects and population bottlenecks
Gene flow- movement of genes among populations
Natural selection is non-random and the only way there can be evolution
Natural selection: Non-random differences in survival and/or reproduction among individual entities on the
basis of differences in heritable characteristics.
Adaptation: 1) a characteristic that enhances the survival and/or reproduction of organisms that bear it,
relative to alternative (especially ancestral) character states; 2) a physical, physiological, behavioural, or
other characteristic evolved through natural selection. Adaptation is NOT the change undergone by an
individual organism during its lifetime in response to external conditions.
Population: for sexual species, a group of interbreeding individuals and their offspring.
Alleles: alternate (i.e., different and mutually exclusive) forms of a gene. e.g., “B” (brown eyes) versus “b”
Genotype: the set of genes possessed by an organism.
Phenotype: the physical expression of the genotype (in combination with the environment).
Frequency: the proportional representation of a phenotype, genotype, gamete, or allele in a population.
e.g., 6 out of 10 have blue eyes = 60% = a frequency of 0.6.
Darwin’s two major objectives
1- Provide convincing evidence that species are related through common ancestry
2- Argue that his mechanism of natural selection could account for changes through time
and he resulting difference among species
Artificial selection is like breeding on purpose
1- Individuals within populations are variable
2- This variability among individuals is at least partly heritable
a. Offspring tend to look like their parents moreso than any other part of the
b. Traits are passed down
3- Not everyone survives and reproduces, and some individuals are more successful than
a. Not every egg is fertilized
4- The differential survival and reproduction of individuals is associated with the heritable
variation among individuals (it is non-random)
a. Offspring that reach adulthood and have offspring of their own are better suited
for survival. b. Some individuals are more successful due to their given traits
Organisms do not evolve- populations do
1. Natural selection by itself does not create new traits, it only changes the proportion of
variation that is already present in the population. Most often, natural selection reduces the
amount of variation in a population because some variants are eliminated.
2. Mutation, not natural selection, is the source of new variation. The repeated two-step
interaction of mutation and natural selection is what leads to the evolution of new adaptive
3. Mutation is random with respect to fitness — that is, it occurs without regard for what
happens to the organism. It is simply a genetic error. Natural selection is, by definition, non-
random with respect to fitness. This means that, overall, it is a serious misconception to
consider adaptation as happening “by chance”.
4. Mutations occur with all three possible outcomes: neutral (no phenotypic effect), deleterious
(bad effects), and beneficial (positive effec