Study Island
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Generation Date: 09/04/2014
Generated By: Kurt Ritter
Theory of Evolution
1. Comparative biochemistry is the study of similarities and differences in _______ among
organisms.
A. vestigial structures
B. development
C. DNA sequences
D. homologous structures
Theory of Evolution
2. The first organisms evolved on Earth around 4 billion years ago. The fossil record indicates
that the first organisms were which of the following?
A. prokaryotes
B. mitochondria
C. eukaryotes
D. plastids
Theory of Evolution
3. In 1966, American biologist Lynn Margulis proposed the theory of endosymbiosis, or the idea
that mitochondria are the descendents of symbiotic, aerobic eubacteria. What does the theory of
endosymbiosis help explain?
A. the evolution of archaebacteria
B. the evolution of eukaryotes
C. the beginning of life
D. the beginning of terrestrial life
Theory of Evolution
4. The theory of endosymbiosis provides a possible explanation for how eukaryotic cells came
into existence. The presence of chloroplasts in photosynthetic organisms is one phenomenon
explained by this theory.
Based on the theory of endosymbiosis, what was the significance of the development of
chloroplasts?
The development of chloroplasts led to the oxygenation of Earth's atmosphere, which
A. allowed the evolution of more complex oxygen-breathing organisms.
The development of chloroplasts led to the initial formation of DNA, which allowed
B. organisms to replicate through asexual reproduction.
The development of chloroplasts caused a large increase in the amount of water on Earth,
C. which led to the existence of living organisms.
The development of chloroplasts caused a large increase in carbon dioxide levels in Earth's
D. atmosphere, which allowed the evolution of organisms that perform cellular respiration.
Theory of Evolution
5. The study of embryological similarities and differences among species is called _______.
A. cooperative anatomy
B. comparative embryology
C. investigative neurology
D. developmental psychology
Theory of Evolution
6. The diagram below shows a variety of animals at different stages of development.
Which of the following statements is supported by this diagram?
Humans undergo more stages of development than other animals, such as salamanders,
A. tortoises, chickens, and pigs.
The developmental stages of animals are radically different; they do not possess any
B. similarities at all.
There are similarities in the developmental stages of different organisms in the animal
C. kingdom.
Diverse organisms in the animal kingdom possess more similarities during the fetal stages
D. of development than during their embryonic stages.
Theory of Evolution
7. Nearly all mammals have seven cervical (neck) vertebrae. This fact implies that
A. predators prefer to eat animals with either six or eight cervical vertebrae.
B. all animals can turn their heads the same amount.
C. all mammals descended from a common ancestor.
D. all mammals have to stretch their necks to obtain food.
Mechanisms of Evolution
8. Which of the following statements is true of evolution?
A. Earth's present-day species evolved from older, identical species.
B. Limited resources discourage the evolution of species.
C. Evolution does not always progress in one set direction.
D. all of these
Theory of Evolution
9. Scientists know that organisms that are more closely related will have DNA sequences more
similar to each other than organisms that are distantly related. Which two organisms below
would most likely have the fewest similar nucleotide sequences in a given gene?
A. lion and horse
B. orangutan and howler monkey
C. scorpion and tarantula
D. alligator and earthworm
Mechanisms of Evolution
10. Allele frequency refers to the fraction of individuals with a particular version of a given gene.
What effect does natural selection have on the allele frequency of a population?
It causes random changes and the allele frequency of certain traits may increase or
A. decrease.
It causes the allele frequency to resemble that of a small number of individuals that became
B. separated from the rest of the population.
It greatly reduces the total population, which increases the effects of genetic drift on allele
C. frequency.
It increases the frequency of alleles that improve a species' survival in a particular
D. environment.
Theory of Evolution
11. Look at the representation of a hillside below. The symbols in each stratus of the crosssection represent fossils of different organisms. Which of the following organisms must have
evolved first?
%*^^*
%$$$###*****
$***$$####@
%###@@!!!!**
@<<<<<++++==
A. $
B. @
C. *
D. #
Mechanisms of Evolution
12. Natural selection causes changes in populations of organisms, not individual organisms,
because
organisms within sexually reproducing populations can only pass on genes that reduce
A. their reproductive success.
differential reproductive success caused by genetic variation is necessary for the process of
B. natural selection.
differential reproductive success caused by acquired behaviors is the most important
C. mechanism of natural selection.
organisms within sexually reproducing populations all have the same genetic information
D. and the same likelihood of survival.
Theory of Evolution
13. The instructions for building proteins necessary for all life functions are coded within an
organism's genetic code. The genetic code of an organism consists of codons, or sequences of
three nucleotides, that each code for a specific amino acid. Amino acids are the building blocks
of proteins.
The amino acids coded by specific codons
A. differ between plants and animals.
B. are different for every organism on Earth.
C. differ between members of different species.
D. are almost universal among all living things.
Mechanisms of Evolution
14. Speciation occurs during the evolutionary development, or phylogeny, of a species. In which
of the following situations can speciation occur?
A. When a population becomes interbred.
B. When two populations are reproductively isolated.
C. When two populations merge to become one population.
D. When a population becomes extinct.
Mechanisms of Evolution
15.
The graph above shows the frequency distribution of a population of fish before and after
scientists engaged in a breeding program over many generations.
Which of the following explanations best describes the program?
The average size of the population decreased because the scientists selected for smaller
A. individuals.
B.
C.
The population spontaneously grew larger.
The average size of the population did not change because no selection occurred.
The average size of the population increased because the scientists selected for larger
D. individuals.
Theory of Evolution
16. What does it mean to say that two different species of organisms are closely related?
A. They live in the same habitat.
B. They have the same preferences in diet.
C. They have a common evolutionary ancestor.
D. They have the same parents.
Mechanisms of Evolution
17. In the living world, there is a great deal of genetic variation. The genetic information of dogs
differs from the genetic information of cats; the genetic information of plants differs from the
genetic information of bacteria; your genetic information differs from your father's genetic
information; and so on.
Which of the following is least likely to be a source of genetic variation among living
organisms?
A. asexual reproduction
B. mutations
C. meiosis
D. sexual reproduction
Mechanisms of Evolution
18. Genetic drift can best be defined as
A.
a change in the allelic frequency within a population due to random chance.
a change in the allelic frequency within a population due to differential reproductive
B. success.
C.
D.
the transfer of alleles from one breeding population to another.
the adaptation of a population due to environmental changes.
Theory of Evolution
19. The fossil record shows that the forelimbs of humans, cats, dolphins, and bats have the same
skeletal elements. These skeletal elements have evolved into different shapes and sizes based on
their function. For example, the flipper of a dolphin is adapted for swimming and the wing of a
bat is adapted for flying.
What do the similarities between the skeletal structures of these four species most likely indicate
about their evolutionary history?
These four species all evolved from a common flying ancestor.
A.
B.
C.
D.
These four species are all descended from the same parent organism.
These four species are not related and do not share a common ancestor.
These four species are distantly related and share a common ancestor.
Theory of Evolution
20. Technology Enhanced Questions are not available in Word format.
Theory of Evolution
21.
Comparison: Percentage Match of Blood Protein Structure Among Four Organisms
Organism
Organism
A
B
C
D
A
Not Applicable
76%
65%
60%
B
76%
Not Applicable
85%
51%
C
65%
85%
Not Applicable
77%
60%
51%
77%
Not Applicable
D
The structure of a certain blood protein was compared among four organisms. Each organism
was compared to each of the other organisms. The level that any two protein structures match
can be found at intersection of the rows and columns.
Based on the data, which of the following organisms are most closely related by evolution?
A. A and B
B. C and B
C. B and D
D. D and C
Theory of Evolution
22. Technology Enhanced Questions are not available in Word format.
Theory of Evolution
23. Over the past century, several scientists around the world have made the following
observations:

New mitochondria and plastids can only be generated by old mitochondria and plastids
through a process similar to binary fission.

Both mitochondria and plastids contain DNA that is similar in shape and size to that of
bacteria.

Mitochondria and plastids are surrounded by two or more membranes whose composition
is similar to a prokaryotic cell membrane.

Mitochondria and plastids are about the same size as bacteria.
These observations led scientists to conclude that
mitochondria, plastids, and other cellular organelles are the result of ancient bacterial
A. infections.
mitochondria and plastids are vestigial structures, and they do not serve a useful purpose in
B. modern organisms.
prokaryotic organisms living inside the cells of other organisms evolved into mitochondria
C. and plastids.
the cells found within multicellular organisms, such as humans, are actually parasitic
D. bacterial cells.
Theory of Evolution
24. Fur seals and sea lions have similar body shapes and features. Based on their anatomy, they
seem to have a relatively recent common evolutionary ancestor.
What further evidence would best substantiate that the two animals have a recent common
ancestor?
A. Ten million year old fossils are found of both animals.
B. Both animals live in the Pacific Ocean.
C. The animals are members of different taxonomic kingdoms.
D. The animals have very similar sequences in their DNA.
Mechanisms of Evolution
25. Peppered moths use the adaptation of camouflage as protection from predators. They may
have a variety of colors or shades, but before the Industrial Revolution, they were typically white
with black speckles. The Industrial Revolution in the 1880s introduced large-scale pollution into
the environment. The pollution resulted in widespread, dark-colored staining of buildings and
trees.
Which of the following was the most likely effect of the Industrial Revolution on peppered
moths in cities?
A.
The peppered moths developed a tolerance to smog and chemical waste.
The population of light-colored moths decreased and the population of dark-colored moths
B. increased.
C.
D.
The peppered moths adapted an improved sense of sight and smell.
Over time, the white, speckled moths were outnumbered by plain white moths.
Mechanisms of Evolution
26. Imagine an earthquake creates a chasm that separates a population of squirrels. The two
populations of squirrels evolve into two separate species. What is the name of the process by
which isolated populations of the same species become new species?
A. genetic variation
B. speciation
C. reproductive isolation
D. natural selection
Mechanisms of Evolution
27. Severe flooding in an area caused a population of minnows to become split into two separate
ponds. Prior to the separation, the male minnows all had a moderate number of spots.
Following the separation, the first pond was filled with larger fish that fed on minnows, so male
minnows with fewer spots were better able to avoid detection by predators. The minnows in the
second pond, however, had very few predators, and female minnows in this pond preferred to
mate with males that had the most spots.
After many generations, the two minnow populations evolved into different species and could no
longer interbreed.
Fish Species
Average # of Spots
Original Species
four to six
New Species 1
zero to two
New Species 2
eight to ten
Which of the following best describes why the two minnow populations evolved into separate
species?
Different selective pressures were acting upon the two populations, leading to an increase
A. in genetic variation and the formation of two new species.
The same selective pressures were acting upon both populations, leading to a decrease in
B. genetic variation and the formation of two new species.
Natural selection acted upon the traits of the minnows in the first pond only, causing these
C. fish to evolve into a new species with new adaptations.
Natural selection acted upon the traits of the minnows in the second pond only, causing
D. these fish to evolve into a new species with new adaptations.
Mechanisms of Evolution
28. An individual hydra is swept by an ocean current to an area of the ocean where no other
hydras reside. The hydra asexually reproduces, as does its offspring, until there is a population of
genetically identical hydra. Is it possible for this population to undergo natural selection?
A. No, there is no genetic variation upon which natural selection can operate.
B. Yes, all populations are capable of undergoing natural selection.
C. No, natural selection does not occur in organisms that reproduce asexually.
Yes, the population will undergo changes in order to become better adapted to the new
D.
environment.
Mechanisms of Evolution
29. A small population of a specific bird species lives on an island in the Pacific Ocean. All of
the birds of this species have a crest of feathers on their heads. The color of the crest can be
orange, yellow, or white. An individual's crest color does not effect its chance of survival or its
reproductive success.
A hurricane hits the island and all of the birds with orange crests are killed, as well as many of
the individuals with yellow and white crests. This causes the gene for orange crests to be lost
from the population.
The loss of the gene coding for an orange crest in the bird population described above is an
example of _______.
A. genetic drift
B. gene flow
C. natural selection
D. genetic recombination
Theory of Evolution
30. Technology Enhanced Questions are not available in Word format.
Mechanisms of Evolution
31. Several species of finch live on the Galapagos Islands. They are very similar in appearance,
but have adapted beaks of different sizes and shapes based on their major food source. Finches
with large beaks eat mainly large seeds and cacti. Finches with small beaks eat mainly small
seeds and insects.
Which of the following best explains the variety of beaks found in finches on the Galapagos
Islands?
Biological evolution only affects the species diversity of plants in an ecosystem.
A.
Evolution through natural selection always causes a decrease in the species diversity of an
B. ecosystem.
C.
D.
Biological evolution does not have any effect on the species diversity of an ecosystem.
Evolution through natural selection can increase the species diversity of an ecosystem.
Theory of Evolution
32.
Look at the organisms in the image above. Which of the following organisms are most closely
related evolutionarily?
A. fish and clam
B. starfish and sand dollar
C. crab and starfish
D. fish and starfish
Mechanisms of Evolution
33. A population of lizards lives on Island A. On nearby Island B, another population of the same
species is present. The lizards on Island A have evolved to have a large frill around their necks.
The lizards on Island B, on the other hand, have evolved to have a much smaller neck frill.
Both islands are colonized by humans and some of the lizards on Island A are transferred to
Island B. The lizards from Island A interbreed with the lizards on Island B. The alleles coding
for the large neck frill are passed onto the offspring resulting from these breedings, introducing
new genetic variation into the population.
The transfer of genetic information that occurs between the two lizard populations above is
known as
A. genetic recombination.
B. gene flow.
C. genetic drift.
D. natural selection.
Theory of Evolution
34.
W.
X.
Y.
Z.
The figures above show the forelimb structure of four extinct species of crawling animals. The
circles represent wrist bones, and the digits extend from the wrist.
All living descendants of this group have three digits attached to a single wrist bone. Based on
the evidence provided, which species diverged from the common ancestor earliest?
A. W
B. Y
C. Z
D. X
Theory of Evolution
35. Charles Darwin originally published the idea that all species have descended over time from
common ancestors. This idea is known as evolution. Evolution is best categorized as
A. an unproven observation about a small number of organisms.
B. a scientific fact that has not been modified since Darwin's time.
C. a scientific hypothesis that has not been researched.
D. a scientific theory that is supported by evidence.
Mechanisms of Evolution
36.
The figure above shows plates made from a culture growing bacteria during specified
generations. The culture has white and dark bacteria. After generation 1, scientists applied an
experimental drug intended to kill the bacteria and kept the experimental drug in the culture
during successive generations.
Which statement best explains the results of the experiment?
The dark bacteria showed resistance to the drug.
A.
B.
C.
D.
Both the dark and the white bacteria showed equal resistance to the drug.
The drug had no effect on the population.
The white bacteria showed resistance to the drug.
Theory of Evolution
37. The theory of endosymbiosis claims that millions of years ago, aerobic bacteria were taken
inside of anaerobic cells through endophagocytosis. The aerobic bacteria then fed on the halfdigested food molecules in the cell's cytoplasm and gained a great amount of energy, which, in
turn, benefited the host cell.
Since both organisms benefited, they formed an endosymbiotic relationship, the bacteria evolved
into organelles, such as mitochondria and chloroplasts, and the aerobic cells evolved into
eukaryotic cells.
Which of the following can be cited as evidence for the theory of endosymbiosis?
Mitochondria contain multiple linear chromosomes similar to those found in eukaryotic
A. cells.
Mitochondria are typically above 50 microns in size, whereas eukaryotic cells are typically
B. smaller than 10 microns.
The ribosomes of chloroplasts are more similar in structure to ribosomes found in
C. prokaryotes than to ribosomes found in eukaryotes.
Eukaryotic cells appeared on Earth around 1.5 billion years ago, whereas chloroplasts
D. appeared on Earth only 2.5 million years ago.
Theory of Evolution
38. Which of the following is a direct observation that could be used as evidence to support the
theory of evolution?
A.
Humans, cats, whales, and bats all have similar forelimb skeletal structures.
Species that have similar DNA sequences are probably closely related in terms of
B. evolution.
C.
D.
Populations that are separated for thousands of years can evolve into diverse species.
Fossils found deeper in the ground are older than fossils found near the surface.
Mechanisms of Evolution
39. A population of deer gets exposed to a pesticide that produces mutations in one of the
following types of cells. In which type of cell will a mutation be most likely to alter the make-up
of the population?
A. muscle cell
B. brain cell
C. sperm cell
D. blood cell
Mechanisms of Evolution
40. Technology Enhanced Questions are not available in Word format.
Mechanisms of Evolution
41. A scientist shines low levels of ultraviolet radiation on a dish containing colonies of ruby-red
bacteria. He then makes several replicate plates from this dish over many generations. He finds
that in addition to the ruby-red color, there are also pink, orange, and light red bacteria.
Which of the following is the best explanation for these findings?
A.
Natural selection produced the changes in the bacterial color.
Mutations occurred in the gene for color of the bacteria, which were passed on to
B. successive generations.
C. The scientist selected new types of bacteria by making plates of successive generations
over time.
D.
One bacterial colony changed its color to better blend in to the media.
Mechanisms of Evolution
42. Speciation is the process by which new species
A. die out.
B. are discovered.
C. interbreed with another species.
D. are formed.
Theory of Evolution
43. Scientists know that organisms that are more closely related will have DNA sequences more
similar to each other than organisms that are distantly related. Which two organisms below
would most likely have the fewest similar nucleotide sequences in a given gene?
A. scorpion and tarantula
B. alligator and earthworm
C. orangutan and howler monkey
D. lion and horse
Mechanisms of Evolution
44. In their first attempts to genetically engineer a cow that will make and secrete human growth
hormones in milk, scientists found that they could insert the growth hormone gene into an
embryonic calf. When the calf matures, it produces the hormone. However, they discovered that
the altered gene gets lost from the genome during meiosis.
What is the best explanation of what will happen in a population of genetically altered cows?
A.
B.
The cows will not reproduce because only females will reproduce the altered gene.
The cows will reproduce, but only males will reproduce the altered gene.
C. The cows will not reproduce because neither males nor females will reproduce the altered
gene.
D.
The cows will reproduce, but neither males nor females will reproduce the altered gene.
Mechanisms of Evolution
45. Technology Enhanced Questions are not available in Word format.
Theory of Evolution
46. Technology Enhanced Questions are not available in Word format.
Theory of Evolution
47. The front leg of an iguana and the wing of a bird look different, but both limbs likely evolved
from the same limb of a shared ancestor.
Structures such as these are said to be _______.
A. homologous
B. vestigial
C. heterogeneous
D. differentiated
Mechanisms of Evolution
48. The drastic reduction in genetic variation that results when a new, isolated population is
established by a very small number of individuals from a larger population is known as
A. the founder effect.
B. gene flow.
C. speciation.
D. natural selection.
Theory of Evolution
49. A scientist is doing research on the evolutionary relationship between whales and
hippopotamuses. Which of the following is a reasonable hypothesis that the scientist could make
about this relationship?
Whales are more closely related to dolphins and porpoises than they are to other marine
A. animals.
B.
How did whales evolve to live in the ocean instead of on the land like other mammals?
Which mammalian species are whales most closely related to in terms of their evolutionary
C. history?
Whales are more closely related to hippopotamuses than they are to cartilaginous fish such
D. as sharks.
Theory of Evolution
50. The following data table summarizes the number of differences in amino acid sequences
found for four different species.
Amino Acid Dissimilarities
for Beta Hemoglobin Protein
A
A
B
C
B
C
D
8
3
5
0
1
5
D
Based on the data table, which two species are most closely related?
A. species B and species D
B. species B and species C
C. species A and species B
D. species C and species D
Theory of Evolution
51. Which of the following facts implies that humans and fish had a common ancestor?
A. Both species have the ability to swim.
B. Both species must expel waste materials.
C. Both species have gill slits when they are embryos.
D. Both species are consumers.
Theory of Evolution
52. The study of structural differences and similarities among living things is called _______.
A. neurology
B. comparative biochemistry
C. embryology
D. comparative anatomy
Mechanisms of Evolution
53. Which of the following is best defined as the transfer of genetic information from one
population to another?
A. gene flow
B. natural selection
C. genetic drift
D. genetic recombination
Mechanisms of Evolution
54. Allele frequency refers to the fraction of individuals with a particular version of a given gene.
What effect does the founder effect have on the allele frequency of a population?
It causes random changes and the allele frequency of certain traits may increase or
A. decrease.
It causes the allele frequency to resemble that of a small number of individuals that became
B. separated from the rest of the population.
It greatly reduces the total population, which increases the effects of genetic drift on allele
C. frequency.
It increases the frequency of alleles that improve a species' survival in a particular
D. environment.
Mechanisms of Evolution
55. A mutation exists in a gene that controls hair growth on the middle digit of human fingers.
Some people have mid-digital hair, while others do not. The gene can be passed from one
generation to the next.
Which explanation best predicts what should happen to this trait over time?
The incidence of mid-digital hair will not change because it offers no selective advantage
A. or disadvantage.
B.
The incidence of mid-digital hair will increase because it offers no selective advantage.
The incidence of mid-digital hair will decrease in the population because it has a selective
C. disadvantage.
The incidence of mid-digital hair will increase in the human population because it offers a
D. selective advantage.
Mechanisms of Evolution
56. All species have a certain amount of genetic diversity within their populations. How is
genetic diversity important to the concept of natural selection?
A. Genetic diversity controls the speed at which natural selection is able to occur.
B.
The more genetic diversity a species has, the less likely it is that natural selection will
occur.
C.
Genetic diversity decreases the generation time of species, which contributes to rapid
natural selection.
D. Without genetic diversity, natural selection cannot occur.
Mechanisms of Evolution
57. In a population of field mice, favorable traits in the mice are likely to _______ over time, and
unfavorable traits are likely to _______ over time.
A. decrease, decrease
B. increase, increase
C. decrease, increase
D. increase, decrease
Mechanisms of Evolution
58. In order to be classified in the same species, a group of organisms must be able to
A. live in a common area.
B. express the exact same genes and phenotypic traits.
C. interbreed and produce fertile offspring.
D. eat similar foods and possess a similar diet.
Mechanisms of Evolution
59. Technology Enhanced Questions are not available in Word format.
Mechanisms of Evolution
60. Some organisms have favorable traits that are well-suited to the environment in which they
live. Organisms with this advantage are more likely to thrive, reproduce, and pass their traits to
future generations than organisms without favorable traits.
This process is known as
A. geographic isolation.
B. reproductive isolation.
C. mimicry.
D. natural selection.
Answers
1. C
2. A
3. B
4. A
5. B
6. C
7. C
8. C
9. D
10. D
11. B
12. B
13. D
14. B
15. D
16. C
17. A
18. A
19. D
20. -21. B
22. -23. C
24. D
25. B
26. B
27. A
28. A
29. A
30. -31. D
32. B
33. B
34. C
35. D
36. A
37. C
38. A
39. C
40. -41. B
42. D
43. B
44. D
45. -46. -47. A
48. A
49. D
50. B
51. C
52. D
53. A
54. B
55. A
56. D
57. D
58. C
59. -60. D
Explanations
1. One of the ways scientists judge whether two species are related is through comparative
biochemistry--the study of organisms' DNA sequences.
While each species has its own unique DNA sequence, sequences of related organisms will be
more similar than sequences of unrelated organisms.
2. The earliest known fossilized organisms are single-celled organisms known as prokaryotes.
Prokaryotes are the simplest form of life found on Earth. Most likely, the first prokaryotes were
archaebacteria, with eubacteria following closely behind.
3. The theory of endosymbiosis is part of the theory of how eukaryotes, or organisms composed
of one or more nucleus-containing cells, first evolved. Endosymbiosis also explains the origins
of other eukaryotic organelles, such as chloroplasts. The fact that both mitochondria and
chloroplasts contain their own DNA is evidence for endosymbiosis.
4. The theory of endosymbiosis claims that millions of years ago, aerobic bacteria were taken
inside of anaerobic cells through endophagocytosis. The aerobic bacteria then fed on the halfdigested food molecules in the cell's cytoplasm and gained a great amount of energy, which, in
turn, benefited the host cell.
Since both organisms benefited, they formed an endosymbiotic relationship, and the bacteria
evolved into organelles, such as mitochondria and chloroplasts, and the aerobic cells evolved
into eukaryotic cells.
The theory of endosymbiosis has important significance in terms of the history of life on Earth.
For example, the development of chloroplasts through endosymbiosis led to the oxygenation
of Earth's atmosphere, which allowed the evolution of more complex oxygen-breathing
organisms, such as humans.
5. Comparative embryology is the study of similarities and differences in embryological
development among species. By locating similarities in development, scientists can determine if
species are related, even if only distantly.
For instance, gills are present in all vertebrate embryos at some stage in development. This
common feature likely means that all vertebrates descended from a common fish-like organism.
6. Diverse organisms in the animal kingdom possess similarities in their developmental stages.
Overall, these similarities are more pronounced during the earlier stages of development (i.e.,
zygote through embryo) than in the later stages (i.e., fetal).
By comparing developmental stages of organisms (and by examining and interpreting fossils),
information can be gained about relationships among living organisms and those that inhabited
Earth in the past. This information is often used to modify and clarify existing classification
systems. By studying embryological development, scientists hope to gain a better understanding
of how different animal species have changed over time and how closely they are related to one
another.
7. Structural similarity is one criterion for determining whether organisms share a common
ancestor. The fact that most mammals have seven neck vertebrae implies that they descended
from a common ancestor and are therefore related.
8. Evolution does not always progress in one set direction.
The evolution of species can be charted by making a diagram that resembles a bush or tree. It
begins with a first species, and then "branches" off into other species that evolved from the first,
and so on.
Throughout the process of evolution, the "branch" of a species can die out completely, remain
mostly unchanged, or branch off many times and change into several new species.
9. Organisms classified into the same genus, family, and even order will have DNA sequences
that are more similar to each other than organisms outside of that grouping. Scorpions and
tarantulas are both invertebrates. Lions and horses are both mammals. Orangutans and howler
monkeys are both primates. An alligator is a vertebrate and an earthworm is an invertebrate.
10. Natural selection encourages the survival and reproduction of individuals who are especially
well-adapted to their environment. This means that natural selection causes increases in the
frequency of alleles that improve the species' survival in a particular environment.
11. Often scientists use relative dating to determine when species evolved. They examine
consecutive rock layers to do this. Organisms fossilized on the highest rock layers must have
died more recently than organisms fossilized on the lowest rock layers.
12. Natural selection is a process by which organisms with traits well suited to an environment
survive and reproduce at a greater rate than organisms less suited to that environment. Natural
selection causes changes in populations of organisms, not individual organisms, because
differential reproductive success caused by genetic variation is necessary for the process of
natural selection.
13. Codons are triplet nucleotide sequences that are derived from RNA as opposed to DNA.
These sequences code for specific amino acids in addition to start and stop codons.
The genetic code is read as a nonoverlapping sequence of codons. The genetic code is almost
universal in that the same codons are assigned to the same amino acids in most living things. It
is only nearly universal because there are some exceptions where a few of the codons differ from
the standard ones. For instance, it has been seen that one or two of the stop codons have been
assigned to amino acids instead.
The fact that the genetic code is the same in nearly all living organisms is evidence that they all
share a common ancestor. That is, it is evidence for biological evolution.
14. The environment differs from place to place. Therefore, populations of the same species
living in different places tend to evolve in different directions. When two populations that are
evolving in different directions become isolated from one another and cannot reproduce with
each other, speciation may occur.
15. The graph shows that the average size of the population increased. You can conclude from
the breeding program that the scientists selected for larger individuals. This is artificial
selection, but demonstrates directional selection.
16. When two different species have similar anatomy and similar DNA, it shows that they have
a recent common evolutionary ancestor.
Since evolution is a very slow process that happens over thousands or millions of years, a recent
common ancestor, in terms of evolution, is still much further back in generations than a parent or
grandparent.
17. There are many sources of genetic variation among living organisms.
Mutations, or changes to an organism's genetic material, are a significant source of genetic
variation.
Sexual reproduction results in an offspring that has a combination of genetic material from its
parents, which contributes to genetic variation.
Meiosis is the process by which sexually-reproducing organisms produce unique gametes, or sex
cells. The unique gamete of one parent can fuse with the unique gamete of another parent to
produce a unique offspring, resulting in increased genetic variation.
Asexual reproduction requires only one parent and produces offspring that are geneticallyidentical to the parent. Therefore, asexual reproduction is least likely to be a source of genetic
variation.
18. Genetic drift is a change in the allelic frequency within a population due to random
chance. It is especially apparent within small breeding populations.
For example, genetic drift can result in an allele being completely lost from a population by
random chance, regardless of whether the allele has any effect on an individual's chance of
survival or its reproductive success.
19. Examining the fossil record can offer new insights into the relationship between species and
their evolutionary history.
The forelimb of humans, cats, dolphins, and bats have the same skeletal elements because these
species most likely are distantly related and share a common ancestor. This common
ancestor most likely possessed these skeletal structures, and each divergent species inherited this
trait from the ancestor. As the new, divergent species moved into different habitats, their
forelimbs adapted based on their function. The original skeletal structure, however, remained the
same.
20. -21. Organisms that have the highest percentage of matching nucleotide sequence in protein
structure are the most closely related by evolution. For this protein, C and B had the highest
level of matching: 85%.
22. -23. Observations over time have led scientists to conclude that prokaryotic organisms living
inside the cells of other organisms evolved into mitochondria and plastids.
This theory, known as the endosymbiotic theory, claims that aerobic bacteria were taken inside
of anaerobic cells through endophagocytosis. The aerobic bacteria then fed on the half-digested
food molecules in the cell's cytoplasm and gained a great amount of energy, which, in turn,
benefited the host cell. Since both organisms benefited, they formed an endosymbiotic
relationship, and the bacteria evolved into organelles, such as mitochondria and plastids, and the
aerobic cells evolved into eukaryotic cells.
24. Anatomical evidence was the data that originally led Charles Darwin to the idea that different
species evolved from common ancestors.
Today, genetic testing of DNA can further support this idea. Animals that have more
similarities in their DNA are more likely to have a recent common ancestor than those that have
fewer similarities.
Different species with a recent common ancestor are said to be related to one another.
25. After the Industrial Revolution began, the pollution began staining buildings and trees in a
dark, blackish color. While on these dark-colored surfaces, the light-colored peppered moths
were much more visible to predators than before. On the other hand, the rare, dark-colored
peppered moths had a new advantage: they camouflaged well with the dark surfaces, and thus
were less visible to predators.
So, the most likely effect of the Industrial Revolution on peppered moths in cities was that
population of light-colored moths decreased and the population of dark-colored moths increased.
26. The accumulation of differences between groups is called divergence. Divergence leads to
the formation of new species through the process of speciation.
27. Different selective pressures were acting upon the two minnow populations, leading to
an increase in genetic variation and the formation of two new species.
Organisms evolve to best fit their environment. When a species is put into new environmental
conditions, this often leads to the formation of a new species. If a population is split, it is
possible for two new populations to form because of different selective pressures acting on the
two populations.
28. Natural selection could not occur if there was no genetic diversity amongst species. In this
case, the only way natural selection could occur is if one of the offspring experiences a genetic
mutation, which would introduce genetic diversity into the population.
29. Genetic drift is a change in the allelic frequency within a population due to random chance.
It is especially apparent within small breeding populations.
For example, genetic drift can result in an allele being completely lost from a population by
random chance, regardless of whether the allele has any effect on an individual's chance of
survival or its reproductive success.
30. -31. The diversity of species is the result of speciation, or the splitting and divergence of former
species into new species. Speciation occurs as organisms evolve to better fit their environment.
For example, the finches on the Galapagos Islands evolved different sized and shaped beaks
based on the food sources that were easily accessible to them.
Evolution through natural selection can increase the species diversity of an ecosystem.
32. Darwin cited animals with similar body plans as having evolved from a common ancestor.
The starfish and the sand dollar both have radial or circular symmetry, while the fish, crab, and
clam have a bilateral symmetry. Therefore, of the animals presented, the starfish and sand
dollar are most closely related evolutionarily.
33. Gene flow is the transfer of genetic information from one population to another. Gene flow
can be caused by many different events, such as pollen being spread to a new area by the wind or
humans transferring animals from one location to another.
Gene flow can be an important source of genetic variation when unique genetic information from
one population is introduced into a different population.
34. Animal Z has each digit attached to a compound wrist bone, while all the others have 3
digits attached to a single wrist bone. This suggests that animal Z diverged earlier than the other
three.
Since living relatives of this group have only one wrist bone, it is likely that the presence of three
wrist bones is the ancestral state. Over time, environmental pressures may have have favored a
reduction in the number of wrist bones. However, evidence from biochemical and fossil records
could help verify this hypothesis.
35. A scientific theory is a widely accepted explanation for a scientific phenomenon that is
supported by extensive amounts of data. Scientific theories can be modified over time as new
information is discovered, but they are rarely discarded.
Therefore, evolution is classified as a scientific theory because it is supported by evidence
gathered through extensive experimentation and observation.
36. The frequency of dark bacteria in the population was low. The presence of the drug reduced
the frequency of the white bacteria and increased the frequency of the dark bacteria. You can
conclude that the dark bacteria were resistant to the drug and were able to reproduce
successfully over time.
37. There is much evidence to support the theory of endosymbiosis. Some of this evidence is
cited below.

The 70S ribosomes of chloroplasts and mitochondria are more similar to the 70S
ribosomes found in prokaryotes than the 80S ribosomes found in eukaryotes.

Eukaryotic cells, mitochondria, and chloroplasts all appeared on Earth at around the same
time - 1.5 billion years ago.

Prokaryotic cells, mitochondria, and chloroplasts are typically smaller than 10 microns,
whereas eukaryotic cells are usually larger than 50 microns.

Prokaryotic cells, mitochondria, and chloroplasts contain one single, circular
chromosome, whereas eukaryotes contain multiple linear chromosomes.
38. An observation is something that can be measured or directly perceived with the senses. A
scientist could examine the skeletons of various species and directly observe that humans, cats,
whales, and bats all have similar forelimb skeletal structures. Structures that are similar
because species share a distant common ancestor are known as homologous structures.
The other answer choices cannot be directly observed; they require making inferences or
conclusions based on interpretations of observations.
39. Natural selection acts upon the mutations that are inherited from one generation to the next.
Of the cell types listed, only the genes in the sperm cell will get passed on to future generations
and will have the potential to alter the make-up of the population.
40. -41. Evolution needs both variations and natural selection to evolve a species. Mutations are
important in how populations change over time because they result in genetic changes to the
gene pool.
In this experiment, ultraviolet radiation induced mutations in the gene for color, which is why
new colors of bacteria appeared. However, since neither nature nor the scientist applied any
selection, the variations in colors remained.
42. Speciation is the process by which new species are formed.
Speciation can occur when groups of the same species become separated by a natural occurrence,
such as formation of a deep gorge.
During speciation, organisms in the various groups develop sufficient genetic differences they
can no longer interbreed with each other.
43. Organisms classified into the same genus, family, and even order will have DNA sequences
that are more similar to each other than organisms outside of that grouping. Scorpions and
tarantulas are both invertebrates. Lions and horses are both mammals. Orangutans and howler
monkeys are both primates. An alligator is a vertebrate and an earthworm is an invertebrate.
44. The altered gene gets lost during meiosis, which produces the reproductive sex cells: eggs
and sperm. The cows will reproduce normally, but none of the offspring will have the altered
gene. So, the presence of the altered gene will not affect the genetic make-up of the population
from one generation to the next.
45. -46. -47. Animals with homologous structures evolved from the same distant ancestor. A horse's leg, a
bat's wing, and a bird's wing appear different, but they all evolved from the limbs of that same
distant ancestor, so they are all homologous.
48. The founder effect is an extreme form of genetic drift that occurs when a few members of a
larger population establish a new, isolated population.
The genetic variation of the new population will be drastically reduced from that of the original
population since only the alleles carried by the founding members will be present in the new
population. Genetic traits from the original population can be lost or over-represented by the new
population, depending on the alleles present in the founding members.
49. A hypothesis is written in a statement rather than question form. For a hypothesis to be valid,
it does not have to be correct, but it must be testable. Statements which are not testable, such as
statements about an animal's emotional state, cannot be hypotheses.
A reasonable hypothesis that the scientist could make on the evolutionary history of whales and
hippopotamuses would be: Whales are more closely related to hippopotamuses than they are
to cartilaginous fish such as sharks. The scientist could then gather evidence to prove or
disprove the hypothesis.
50. Species of organisms that are more closely related have fewer differences in their sequences
of amino acids. Similarities in amino acids reflect a similarity in DNA because DNA sequences
determine which amino acids are produced.
Based on the amino acid sequences for beta hemoglobin protein, species B and species C are
most closely related because they have the fewest difference in their amino acid sequences.
51. Both species have gill slits when they are embryos.
In fish, gill slits are retained after birth. In humans, however, the gill tissue develops into the jaw,
tongue, larynx, and middle ear.
Scientists use similarities in embryonic development to determine whether species share a
common ancestor. In this case, humans and fish seem to be related, even if the relation is distant.
52. The study of structural differences and similarities in living things is called comparative
anatomy. Much can be learned by comparing the structural similarities and differences of living
things.
For example, the identification of homologous structures, or structures in different species that
may look different but have origins in a common ancestor, implies that the species are related.
Also, the identification of vestigial structures, non-functional remnants of structures that were
operational in a distant ancestor, can also imply relatedness between two species.
53. Gene flow is the transfer of genetic information from one population to another. Gene flow
can be caused by many different events, such as pollen being spread to a new area by the wind or
humans transferring animals from one location to another.
Gene flow can be an important source of genetic variation when unique genetic information from
one population is introduced into a different population.
54. When a small number of individuals become separated from the rest of the population and
breed only among each other, the allele frequency in this population is mostly determined by
the allele frequency of the founding members, which is why it is called the founder effect. The
founder effect is a kind of genetic drift.
55. Whether you have mid-digital hair or not gives you no special advantage or disadvantage for
survival. So, natural selection does not change the frequency of this gene in the population.
Therefore, the incidence of mid-digital hair should not change in the human population.
56. Natural selection could not occur if there was no genetic diversity amongst species.
Furthermore, the process of natural selection, which leads to speciation, can enhance the genetic
diversity of species.
57. If an organism dies before reproducing, then its unique traits will be eliminated from the
population. On the other hand, if an organism has favorable traits that allow it to survive and
produce many offspring, then its traits will be more prevalent within the population.
So, over time, favorable traits in a population of field mice are likely to increase, and
unfavorable traits are likely to decrease within the same population. In this way, natural
selection plays an important role in the way a species changes over time.
58. Species are reproductively distinct groups of organisms. That is, in order to be classified in
the same species, a group of organisms must be able to interbreed and produce fertile
offspring.
59. -60. Favorable traits are traits that promote an organism's success in a particular environment.
Organisms with favorable traits are more likely to thrive, survive, and reproduce than organisms
without favorable traits. In this way, nature "selects" which traits (or even which types of
organisms) will continue to exist in a population.