1. What is evolution?
Evolution is genetic change in a population over time.
2. How did people think that species arose and diversified before Charles Darwin
published his theory of evolution by natural selection?
The major belief was in a special creation in which God formed all species and placed
them on the earth. Jean Baptiste de Lamarck proposed that acquired characteristics were
heritable; differential use and disuse of body parts accounted for changes between
generations and species diversification.
3. What did Darwin observe that led him to develop his ideas about the origin of species?
As Darwin journeyed in the HMS Beagle, he observed the uniformity of geological
processes such as volcanism, earthquakes, and erosion. He collected fossils and observed
that each continent had animals that were characteristic and different from those on other
continents. On the Galapagos, he observed and collected finches from different islands
and noted differences in giant tortoises on different Galapagos Islands. These
observations led Darwin to the idea of “descent with modification.”
4. How is artificial selection different from natural selection?
In artificial selection, humans select for the traits they desire in plants or animals. In
natural selection, environmental factors favor some traits over others.
5. How did Darwin’s ideas challenge prevailing beliefs about life’s diversity and the
status of humans?
Darwin’s ideas challenged prevailing beliefs about life’s diversity by using natural
processes to explain how species arise. Darwin saw humans as just another species and
rejected the idea that humans were specially created. He thereby demoted humans from
an exalted position, putting them on an equal footing with other species competing for
6. What is the modern evolutionary synthesis?
The modern evolutionary synthesis combines the work of Darwin with a modern
understanding of genes, chromosomes, and the origins of variation.
11.2 1. What is an adaptation, and how do adaptations become more common within a
An adaptation is a characteristic that helps an individual survive and reproduce in its
environment. Adaptations become more common within a population when they are
heritable and when they increase the odds of survival and reproduction.
2. What is the role of genetic variation in natural selection?
Genetic variation is the raw material that natural selection acts on since genetic variation
creates variations in phenotypes, some of which are better suited to the current
3. How can natural selection favor different phenotypes at different times?
Natural selection can favor different phenotypes at different times because environments
are always shifting in dramatic or subtle ways.
4. Why doesn’t natural selection produce perfectly adapted organisms?
Natural selection does not produce perfectly adapted organisms because each
population’s evolution is constrained by its existing gene pool, which limits the possible
allele combinations and may not contain every allele necessary to confront every
challenge. Chance events may also wipe out adaptive allele combinations. Genetic
illnesses that produce symptoms only after reproductive age also can maintain harmful
alleles in a population.
5. What is evolutionary fitness?
Evolutionary fitness is measured by reproductive success.
1. What are the five conditions required for Hardy–Weinberg equilibrium?
The five conditions required for Hardy-Weinberg equilibrium are:
- no mutations;
- random mating;
- no emigration or immigration;
- the population is large enough to eliminate random changes in allele frequencies
- natural selection does not occur.
2. Why is the concept of Hardy–Weinberg equilibrium important? The concept of Hardy-Weinberg equilibrium is important because it shows that evolution
has the potential to occur at all times; in fact, evolution is probably occurring at all times
in all populations.
3. Explain the components and meaning of the equation p + 2pq + q = 1. 2
In the Hardy-Weinberg equation, p= the frequency of the dominant allele in a population,
q= the fre2uency of the recessive allele, and pq= the product of p and q. The equation p
+ 2pq + q = 1 says that all individuals in a population are homozygous dominant,
heterozygous, or homozygous recessive (for a gene with only two alleles). By applying
the Hardy-Weinberg equation at different times, it is possible to observe changes in allele
frequency and determine whether evolution is occurring.
4. Why doesn’t Hardy–Weinberg equilibrium occur in real populations?
Hardy-Weinberg equilibrium does not occur in real populations because the conditions
for it are never met in real populations.
1. Distinguish among directional, disruptive, and stabilizing selection.
Directional selection selects against phenotypes at one end of the variation spectrum in a
population; the variation in the population shifts in the opposite direction. In disruptive
selection, extreme phenotypes are more fit than the intermediate phenotype; the
frequency of the intermediate phenotype decreases in the population. In stabilizing
selection, both extreme variations of phenotype are selected against; the most common
phenotype in the population remains around the median.
2. How can natural selection maintain harmful alleles in a population?
Natural selection can only select against phenotypes. If the dominant phenotype is
selected for, heterozygous individuals will retain the recessive allele in the population.
Also there are times when the heterozygous condition gives advantages to the individual
(e.g., cystic fibrosis carriers are less susceptible to cholera). In these instances a balanced
polymorphism is seen in the population.
1. How does sexual selection promote traits that would seem to decrease fitness?
Sexual selection selects for extreme phenotypes in one sex, and those extreme variations
often place the individual at a disadvantage for survival (e.g., a peacock’s longer tail will
make him more visible to predators and slower in escaping). However, since these traits
increase fitness by increasing mating success, sexual selection remains an active force in
the population. 2. What is the difference between intrasexual selection and intersexual selection?
Intrasexual selection occurs when members of the same sex compete for mating
opportunities with the opposite sex. Intersexual selection occurs between males and
females of the same species: one sex chooses a mate of the other sex based on the
presence of a characteristic.
1. What are some ways that mutations affect an organism’s phenotype?
Mutations introduce new alleles, which may or may not alter the phenotype of an
2. Under what conditions does a mutation in one organism pass to subsequent
A mutation in one organism passes to subsequent generations if it is a mutation that can
be inherited. In sexually reproducing organisms, the mutation must appear in a gamete-
producing cell. Mutations in somatic cells will not be passed to the next generation. By
contrast, a mutation in an organism that produces asexually will be transmitted to all of
3. How does sampling error cause genetic drift?
Sampling error occurs when the selected sample (e.g. the alleles making it to the next
generation) does not match the larger original pool. Such chance sampling errors result
in a change in the allele frequencies of the population, not as a result of adaptive fitness,
but as a result of pure chance.
4. What is the difference between the founder effect and a population bottleneck?
In the founder effect, a new population is started by a small group of individuals that
colonize a new area. In a population bottleneck, a large and genetically variable
population experiences a massive die-off, and only a few individuals survive to continue
the population. Both effects result in populations with restricted variety in their gene
pools and are therefore prone to genetic drift.
5. How do nonrandom mating and gene flow disrupt Hardy–Weinberg equilibrium?
Nonrandom mating means that not all individuals have an equal chance of reproducing,
and this will shift the equilibrium equation. In gene flow, alleles enter or leave the
population; this by its very nature disrupts the allele balance in the population.
11.7 1. What hypothesis did Conover and Munch test?
The researchers tested the hypothesis that fishing results in population shifts towards fish
that are smaller at maturity or that mature more slowly.
2. How is a population reared in a tank different from a population in the “real world”?
In the real w