Unit 3 Test
Adaptation and Specialization
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: 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.
The Basis Of Natural Selection
When it comes specifically to adaptive changes among species and the traits of organisms that allow
them to survive successfully in their environments, natural selection is indeed the only known mechanism
that can provide a scientific explanation.
1. Individuals within populations are variable.
That not every individual is identical in a population is obvious for humans
2. This variability among individuals is at least partly heritable.
Offspring tend to look more like their parents than like unrelated members of the population
3. Not everyone survives and reproduces, and some individuals are more successful than others.
Many more offspring are produced in each generation than could possibly survive, a phenomenon known
4. The differential survival and reproduction of individuals is associated with the heritable variation among
individuals (i.e., it is non-random).
This is the key to natural selection, that the individuals who do manage to reach adulthood and have
offspring of their own are, on average, better suited to surviving and reproducing in their particular
environment because of traits that they inherited from their parents.
10 Things about Natural Selection
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 effects). Beneficial mutations may be rare and deliver only
a minor advantage, but these can nonetheless increa