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MCAS Evolution

Feb 2016 MCAS.  Scientists often compare fossils of extinct organisms with living organisms to help determine evolutionary relationships. What is the primary information that scientists use when comparing fossils with living organisms?

A. the types of minerals that formed the fossils
B. the size of the rocks that contained the fossils
C. the cause of death for the fossilized organisms
D. the physical characteristics of the fossilized organisms


Feb 2016 MCAS .

The pictures below show the shells of some species of land snails found on a Pacific island. Each species was found on a different hill on the island. Based on the snails’ shell shapes, scientists made hypotheses about the evolutionary relationships among the snails. Which of the following would be the best characteristic to compare in order to test these hypotheses?

Snail shells 16

A. the size of the snails
B. the diet of the snails
C. the DNA of the snails
D. the average age of the snails


Scientists hypothesized that several species of frogs called tiger frogs evolved from a recent common ancestor. The hypothesis was based on fossil evidence and on physical similarities among living species.

Which of the following provides the best additional support for the scientists’ hypothesis?

A. Tiger frogs have longer life spans than other frog species.
B. Tiger frogs have the same diet and all use enzymes to digest food.
C. Tiger frogs live near each other and are all preyed upon by the same predator species.
D. Tiger frogs have similarities in their mitochondrial DNA that are not shared by other frog species.


Spring 2017

Some populations of Atlantic tomcod fish have an allele that makes the fish resistant to toxic pollutants called PCBs. Tomcod populations in several rivers were analyzed for the presence of this allele. Each river had varying levels of PCB pollution. Which of the following results would best support the conclusion that natural selection is influencing the presence of this allele in the tomcod populations?

A. All of the tomcod in each of the rivers have this allele.

B. The percentage of tomcod with this allele remains the same from year to year in each river.

C. The rivers with high PCB levels have larger percentages of tomcod with this allele than the rivers without PCBs.

D. Eggs from tomcod without this allele can hatch in rivers with or without PCBs, and eggs from tomcod with this allele can only hatch in rivers without PCBs.


Spring 2017.

A researcher observed army ants, which form colonies with one queen ant and many worker ants. The researcher observed worker ants moving from place to place to hunt and collect a variety of food for the colony. The queen ant was observed mating with a male ant from another ant colony. The queen produced many eggs after this mating. Which of the following could help increase the genetic diversity in the colony of army ants?

A. the queen ant mating with the ant from a different colony
B. the worker ants collecting the food for the colony to eat
C. the worker ants moving from place to place
D. the queen ant eating a variety of food


Scientists discovered a 375-million-year old fossil in Canada. The diagram below shows the top and side views of the fossil.

Transitional form fossil amphibian
Which observation would best support the hypothesis that this organism was
a transitional form between amphibians and fish?



A. The fossil has a long body, which both modern amphibians and modern fish have.
B. The fossil is larger than most modern amphibians, but smaller than most ancient fish.
C. The fossil has some body structures that are similar to amphibians and some body structures that are similar to fish.
D. The fossil was discovered near a lake, which shows that the organism
needed water to reproduce, as do amphibians and fish.


Some plants in an area produce a toxin that protects them from being eaten by a variety of insect species. The toxin decreases reproductive rates in insects. Because of a genetic mutation, some fruit flies can detect the plant toxin and therefore avoid eating the plant.

a. Describe how the number of fruit flies in the population that can detect the toxin will most likely change over the next 25 years.

b. According to the mechanism of natural selection, explain how the change you described in part (a) will occur.

c. Based on the changes in the fruit fly population, describe what will most likely happen to the plants’ production of the toxin. Explain your answer.


Sperm whales have vestigial hip bones, and a small percentage of sperm whales
also have vestigial hind limbs. Which of the following statements best explains
the presence of these vestigial structures in sperm whales?

A. Sperm whales evolved from ancestors that walked on land.
B. Sperm whales are in the process of evolving into land mammals.
C. These structures are acquired by each individual sperm whale during its lifetime.
D. These structures resulted from sperm whales having a long period of embryonic development.


2014 MCAS Open response question

An elephant shrew and a shrew are pictured below.

Elephant Shrew and shrew

For many years, scientists had classified elephant shrews in the same family as shrews. In the 1990s, however, scientists gathered evidence for the evolutionary tree below and reclassified elephant shrews into a different family from shrews.

MCAS Elephant Shrew cladogram phylogeny

a. Describe the most likely reason why scientists originally classified elephant shrews with shrews.

b. Using the evolutionary tree, identify the groups to which elephant shrews are most closely related.

c. Identify and explain the evidence scientists most likely used to build the evolutionary tree and reclassify elephant shrews.

d. Identify one other type of evidence that scientists use to determine evolutionary relationships and build evolutionary trees.


Scientists measured and recorded the average body size in a bird population over time. One year, a period of cold weather killed many of the birds. A few generations later, the scientists observed that the average body size in the population was larger than it had been before the cold weather. The scientists concluded that the population had evolved through natural selection. Which of the following would provide the best evidence to support the scientists’ conclusion?

A. The size of the bird eggs also increased over time.
B. The birds with the largest body size were the males.
C. The frequency of alleles for body size changed in the bird population.
D. The number of birds in the population had decreased by 50% or more.


The three-spined stickleback is a species of fish. It lives in the ocean and in streams that flow into the ocean. Some scientists think that the ocean populations and stream populations may be evolving into separate species. Which of the following statements describes how speciation of these fish would most likely occur?

A. Fish from stream populations would start to reach maturity at the same time as fish from ocean populations.

B. Fish from stream populations would sometimes swim into the ocean but fish from ocean populations would stop swimming into streams.

C. Ocean populations and stream populations would each mate fewer times per year and would have decreased birth rates over time.

D. Ocean populations and stream populations would each adapt differently to their environments and would accumulate enough differences over time to prevent interbreeding


In a certain insect species, body color varies from very light gray to very dark gray. These insects are eaten by birds that find their prey by sight. A brush fire occurs, blackening the ground where one population of this insect species lives. Which of the following is most likely to occur over the next few years?

A. The body color in the population will mutate to black.
B. The percentage of very dark gray individuals will increase.
C. The distribution of body color in the population will not change.
D. The very light gray individuals will learn how to reproduce at a later age.





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