Evolution Review
1. What is the difference between natural selection and gene flow?
Natural selection relies on organisms exhibiting a variation in traits. The most fit
organisms for that environment will survive to reproduce (differential reproduction).
The surviving organisms will be more likely to express the adaptive trait.
Gene flow is the transfer of genes from one population to another as a result of
immigration. These genes will be expressed as expected per Mendelian inheritance,
where applicable.
2. Define adaptations and explain how they help plants and animals survive in different environments.
A physical structure or behavior which contributes to the fitness of an organism in its
environment.
3. Give an example of how an adaptation in different species has a similar benefit.
Two different bacteria can gain immunity to a particular antibiotic. While their
mechanisms and gene sequences may be different, the results are equally effective.
4. How can adaptations in mole rats help you understand how natural selection has affected them?
(page 396-397)
Mole rats likely resembled rock rats to begin with. As a result of predation, rats with
long claws and teeth were selected for, and the population overall became represented by
these traits. Additionally over time, vision lacked a benefit to the mole rat, who spent its
time underground. Being as vision was no longer a survival advantage, they lost their
vision.
5. Which answer BEST shows an animal’s adaptation to the tropical rain forest?
a. camouflage in a tree frog
c. an elephant’s long trunk
b. the long neck of a giraffe
d. migration of birds in winter
6. What are fossils and how can they be helpful to scientists?
Fossils are the preserved remains of animals, plants, and other organisms from the
remote past. They help scientists understand the geography of the world through time,
and the organisms that lived on it.
7. While looking for fossils on an eroded hillside, you discover fossil coral and fish in one layer. In a
layer just above, you find the fossil imprint of a fern frond and some fossil moss. Assuming the rock
has not been disturbed, which of the following is the most probable conclusion?
That at some point in the past, the area was an aquatic (water) environment, but changed
to a terrestrial (land) environment.
8. What role do predators play in natural selection and what physical characteristics could benefit
them?
Predators help drive natural selection by preying on those less fit for their
environment. Survivors pass on the traits that assisted them in avoiding predation.
9. Explain homologous structures and give an example.
Homologous structures may not necessarily perform the same function but they share a
common ancestral origin.
For instance, the forelimbs of humans and bats are homologous structures. Although
they are used differently, the basic skeletal structure is the same and they are derived
from the same embryonic origin. Their similarity in this regard could indicate a
likely evolution from a common ancestor.
10. What are analogous structures and give an example.
Analogous structures pertain to the various structures in different species having the
same appearance, structure or function but have evolved separately, thus do not share
common ancestor.
Examples of analogous structures include:

wings of insects and birds used for flying

jointed legs of insects and vertebrates used for locomotion

fins of fish and flippers of whales (mammals)
11. Define vestigial structures and give an example.
Vestigial refers to an organ or part (for example, the human appendix) which is greatly
reduced from the original ancestral form and is no longer functional or is of reduced or
altered function.
Vestigial structures provide a clue to the evolutionary history of a species because they
are remnants of structures found in the ancestral species.
12. Upon close examination of the skeleton of an adult python, a pelvic girdle and leg bones can
be observed. These features are an example of _________.
a. artificial selection
c. vestigial structures
b. homologous structures
d. comparative embryology
13. Define speciation and explain what causes speciation.
Speciation happens when a population becomes geographically isolated, and each new
population adapts to their new environment. The two populations maintain different
allelic frequencies.
14. What are geographic and reproductive isolation?
Geographic isolation refers to a situation where a species, or a population of a species,
becomes separated by a physical barrier (a lake, ocean, mountains, etc.), allowing each
group to diverge along separate evolutionary paths. The effect of geographic isolation is
that the two populations are subjected to different selection pressures, since the
conditions in the two areas will be different. So different alleles will be selected for, and
genetic differences will gradually accumulate between, the populations. In time, enough
genetic differences will occur so that the two populations will no longer interbreed. Then,
by definition, they have become different species.
The environment may impose an external barrier to reproduction, such as a river or
mountain range, between two incipient species but that external barrier alone will not
make them separate, full-fledged species. Allopatry may start the process off, but the
evolution of internal (i.e., genetically-based) barriers to gene flow is necessary for
speciation to be complete. If internal barriers to gene flow do not evolve, individuals
from the two parts of the population will freely interbreed if they come back into contact.
Whatever genetic differences may have evolved will disappear as their genes mix back
together. Speciation requires that the two incipient species be unable to produce viable
offspring together or that they avoid mating with members of the other group.
15. Define extinction and explain what factors could make a species more susceptible to becoming
extinct.
Extinction is the end of an organism or of a group of organisms (taxon), normally
a species. The moment of extinction is generally considered to be the death of the last
individual of the species, although the capacity to breed and recover may have been lost
before this point.
A species can become susceptible to extinction if there is little genetic variance in their
population, or their environment becomes unstable.
16. How can mutation be an advantage for an organism?
A mutation can introduce an adaptation that becomes favorable to the environment,
increasing the fitness of that organism to that environment, That organism will therefore
survive to pass on its genes, increasing the frequency of that allele in the population over
time.
17. Which combination of characteristics in a population would provide the greatest potential for
evolutionary change?
a. small population, few mutations
c. large population, few mutations
b. small population, many mutations
d. large population, many mutations
18. Looking at the graph on page 400, describe the changes in the evolution of the camel.
Many changes happened over time: the structure of the tooth changed (likely in response
to a changing food source). The foot changed from toes to hoof. There is evidence that
elongated legs, and increased body size were advantageous over time.
19. Natural processes, such as speciation and gradualism, provide the genetic basis for_______.
a. evolution
c. biogenesis
b. spontaneous generation
d. sexual reproduction
20. What is evolution? Who first stated the theory of evolution?
Evolution is the idea of change over time, as first hypothesized by Charles Darwin.
21. List and describe 5 pieces of evidence that support the theory of evolution.
1. Universal genetic code 2. Fossil evidence 3. Commonalities in genetic sequences
between living organisms 4. Commonalities in pacing and sequencing of embryos 5.
Bacterial resistance to antibiotics.
22. Based on the fossil record shown in the picture above, explain what has happened to the type
of habitat found in the area as time passed.
A terrestrial (land) habitat turned into a marine (water) environment. This can be
determined because the oldest organisms are trees, and the most recent fish.
23. Create a graphic representation for disruptive, stabilizing, and directional selection and explain
what is happening in each circumstance.
Disruptive selection favors the EXTREMES. Stabilizing selection favors the AVERAGE.
Directional favors ONE EXTREME OVER ANOTHER.