Article 1

Investigating the Inconsistencies in College Student Responses to Natural Selection Test Questions

by John Settlage , Cleveland State University, and Murray Jensen University of Minnesota



This study was designed to investigate whether a student's responses to test questions about natural selection were influenced by the extent of the student's identification with the organism. The hypothesis was that students would be reluctant to invoke the ravages of natural selection upon species with which they possessed a greater empathy than upon species about which they cared less strongly. This "pulling for the furry guy" outlook is being called "the Disney effect."
Several studies examining students' understanding of evolution by natural selection have appeared in the science education research literature (Bishop & Anderson, 1990; Demastes, Settlage, & Good, 1995; Demastes, Good, & Peebles, 1996; Jensen & Finley, 1995; Settlage, 1994; Tamir & Zohar, 1991). Students' explanations of evolution represent a complex mixture of ideas relating to Lamarckian evolution, Darwin's theory, and teleological reasoning, with the students' conceptions repeatedly proving to be resilient to change (Deadman & Kelly, 1978; Brumby, 1979; Halldén, 1988). To further compound the problem of teaching evolution, students respond to questions about natural selection in different ways depending upon the species in question. For example, Demastes, Good, and Peebles (1995) found that during individual interviews, high school students became, over one school year, more capable at applying evolutionary principles to various scenarios. However, some students were reluctant to extend the possibility of natural selection to include humans. This suggests that students struggle to apply the principle of "survival of the fittest" to organisms that are perceived as more like themselves.

The history of taxonomic systems provides insights into what organisms humans consider to be more and less like themselves. The Great Chain of Being depicted nature as a highly structured system based on a hierarchical, linear pattern (Bowler, 1983). The hierarchy placed humans at the top (most superior) and inert objects at the bottom (Appendix 1). This classification scheme was initially developed by the Greeks and was extensively used into the early 1800s. One intent of the chain was to show the divine plan of creation: a very orderly, well-thought-out design. The Chain of Being model lost popularity when more and more species were discovered and the relationships between them could no longer be explained through a simple linear hierarchy (Gould, 1985).

Though the Chain of Being is not taught in most biology courses, students still identify organisms as being more and less like humans, and it is our assumption that the more closely students identify an organism with humans, the less likely they will perceive the organism to endure the negative effects of natural selection. For example, students employing a Great Chain of Being mindset might feel that dogs would be less affected by a selection event than bacteria because dogs possess more human qualities; they are closer to the top of the chain than are bacteria.

We predict the existence of the Disney effect for two reasons. First, students have been found to recapitulate historical views in their own explanations of natural phenomena (Wandersee, 1985; Jensen & Finley, 1995; Jensen & Finley, in press) and remnants of ideas about the Chain of Being are still present in our language (e.g., "advanced" and "primitive"). For many students, the term "advanced" relates to intelligence (the ability to out-smart natural selection) and/or morphological complexity, whereas "primitive" implies an organism's relative simplicity, making it a more plausible target for selection events.

The second reason the existence of the Disney effect was hypothesized is the prevalent anthropomorphic depictions of animals in popular media. Children's movies and stories frequently portray nature in unrealistic terms: predators rarely eat but still survive, potential prey successfully avoid selection events, and specific instances of individual death are but rarely presented. Hundreds of examples of inaccuracies can be found in children's literature, all potentially influencing students' views of nature before entering a biology course.


Two groups of general biology students at a large midwestern research university were administered a twelve-item multiple-choice test [version B of the two-tier test "Understanding Biological Change" (Settlage & Odom, 1995)] to assess the extent of their understanding of natural selection. (See Appendix 2 for the instrument.) The test consisted of six parallel items describing evolutionary scenarios. The difference between parallel items was in the life form depicted in the scenario (see Figure 1). One group of students was taught during the spring of 1995 (n = 51) and the other was taught during the fall of 1995 (n = 79). The evaluation took place, in both sections, at the end of the quarter after the evolution instructional unit had been completed.

Figure 1: Sample parallel test items from the Understanding Biological Change test, version B (Settlage & Odom, 1995).

Question 4:  Seals                Question 10:  Bats                

Seals that live in Alaska have a  Bats that feed at night have a    

fat layer.  Their ancestors may   very sophisticated sense of       

not have had fat as thick as it   hearing.  Their ancestors may     

is today.  Over the centuries,    not have heard as well as bats    

changes in the seals have         of today.  Over the centuries,    

occurred since:                   changes in the bats have          

                                  occurred since:       

1.  the need to keep warm caused                                    

the fat of every seal to get      1.  the need to feed at night     

thicker,                          caused the hearing sense of       

2.  more seals each generation    every bat to increase,            

have had thicker fat,             2.  more bats each generation     

                                  have had better hearing,     &n

BECAUSE                                         &n

                                  BECAUSE        &

A.  the seals wanted to adapt to                                    

their surroundings.               A.  the bats wanted to adapt to   

B.  the offspring inherited a     their surroundings.               

thicker layer of fat from their   B.  the offspring inherited       

parents.                          better hearing from their         

C.  the few individuals that had  parents.                          

a thicker fat layer lived to      C.  the few individuals that had  

produce offspring.                better hearing lived to produce   

                                  offspring.       &nbs

After responding to the twelve two-tier test items, the students were presented with six lists of organisms. Each list contained four organisms, two of which appeared in the test as parallel test items (the other two organisms within each foursome were from version A of the Understanding Biological Change test). For three lists, the students were to rank the organisms on the basis of their relative "appeal," with the term left to the students' interpretation. On the other three lists, the students were to rank the sets of four organisms according to how "advanced" they felt the organisms were relative to each other. The intention of the ranking activity was to identify each student's disposition toward the organisms in the natural selection scenarios provided in the test items. There was some uncertainty about whether the Disney effect, if it in fact existed, could be attributed to an individual's affection for one organism over another or to the fact that the individual had a greater regard for one organism because it resided higher on the Great Chain of Being. The decision to ask for both "appeal" and "advancement" rankings was with the intention of investigating both possibilities.

Responses on the two-tier items were subjected to two different types of statistical analysis; the first was chi-square. Six separate tables were constructed, one for each pair of parallel test items. Student responses were considered correct when they selected the desired response on both tiers. Data were coded dichotomously, correct or incorrect. A total of 130 tests provided usable data. The frequencies in the 2 X 2 tables reflect how consistently the students responded to parallel items (Tables 1 & 2). Student responses were not randomly distributed: chi-squared values (df = 1) ranged from 27.607 to 57.767, all of which were significant (p < .001).

Table 1: Distribution of responses to parallel items on Understanding Biological Change test, version B (n = 130). 

A             Bullfrogs            

              0      1      TOTAL  

Sharks 0      50     15     65     

       1      7      58     65     

       TOTAL  57     73     130    

B             Butterflies          

              0      1      TOTAL  

Birds  0      31      9     40     

       1      21     69     90     

       TOTAL  52     78     130    

C              Evergreens           

               0      1      TOTAL  

Raccoon 0      55     22     77     


        1      8      45     53     

        TOTAL  63     67     130    

D             Bats                 

              0      1      TOTAL  

Seals  0      40     15     55     

       1      14     61     75     

       TOTAL  54     76     130    

E             TB bacteria          

              0      1      TOTAL  

Locust 0      50     17     67     

       1      18     45     63     

       TOTAL  68     62     130    

F             Lizards              

              0      1      TOTAL  

Moths  0      16      6     22     

       1      16     92     108    

       TOTAL  32     98     130    

The data indicate that students were fairly consistent in their success on parallel items (see Table 2). For the six pairs of parallel items, the number of students who responded correctly on one item but not on its partner ranged from 22 (16.9%) for item pairs A and F to 35 (26.9%) for item pair E. In other words, the pattern of student responses suggests the instrument was reliable since no fewer than 70% of responses to both items were both right or both wrong on parallel items. Statistics support the speculation about the instrument's quality: reliability for Version B of the Understanding Biological Change test, when calculated as a Spearman-Brown coefficient, was 0.835.

Table 2: Frequency of discrepant responses to parallel items on Understanding Biological Change test, version B (n = 130). 

Parallel       Frequency              Percent             

items                                         &nbs

A              22 / 130               16.9%             

B              30 / 130               23.1%             

C              30 / 130               23.1%             

D              29 / 130               22.3%             

E              35 / 130               26.9%             

F              22 / 130               16.9%             

Totals         168 / 780              21.5%               

Although the instrument proved to be highly reliable, the number of students who had differential success on parallel items was substantial (21.5%); subsequent analyses were based upon these particular responses. For this analysis, the "appeal" and "advancement" rankings were used. Whenever a student had selected the correct response on one item but not the other in a parallel pair, the ranking of the organisms was tabulated. In spite of the initial intention to keep "advancement" and "appeal" rankings separate, the attenuated sample size precluded analysis. Consequently, the decision was made to collapse rankings into relative "preference" and continue the statistical analyses without maintaining the distinctions.
For all discrepant responses, the relative rankings for the organisms included in the particular items were examined. The organism receiving the higher ranking was considered "preferred," regardless of the difference in the values ascribed to the organisms. In other words, one organism was coded as preferred over the other if the ranking difference was small (2 versus 3) or large (1 versus 4). Because some students did not provide decipherable responses on the ranking section of the test, the sample size became reduced further.

The data were arranged into 2 X 2 tables and subjected to a chi-square analysis (see Figure 2). Recall that the Disney effect posits that students will be less likely to apply natural selection principles to organisms with which they have greater empathy. If a student expressed a preference for Organism #1, then the response on this pair of parallel items fell within the first row. Furthermore, if the Disney effect was at work, then the student would be more likely to NOT select the correct answer on the test item describing that organism (cell B). Likewise, should a student express a preference for Organism #2 and be subconsciously reluctant to employ natural selection to explain its evolution, that student's response would fall within cell C. If the Disney effect explains the discrepancy in individuals' responses, we would expect smaller frequencies for cells A and D and greater frequencies in cells B and C.

Figure 2: Frequency table template designed to investigate for the presence of the Disney effect. 

                                   Correct response ONLY on parallel   

test item that describes            

Organism #1       Organism #2       

Preference for   Organism #1       A                 B            &n

Preference for   Organism #2       C                 D            &n

The instrument retained its highly reliable nature with this group of students. The reliability, as calculated with KR-20, was 0.868 with a mean score of 6.985 and a standard deviation of 3.673. Because the Understanding Biological Change test (version B) had such high reliability, the frequency of inconsistent responses on parallel test items caused there to be fewer than thirty sets of responses for the chi-square analysis, as appears in Table 3. The chi-square values for the six tables ranged from 0.00 to 0.89 (df = 1). None of these values represents a statistical significance (p values from 0.344 to 1.00). These data do not support the existence of a Disney effect. The numbers indicate that the discrepancies in student responses cannot be explained by the relative preference the students ascribed to the organisms depicted in the test items.

Table 3: Cross-tabulations of contradictory responses on parallel items compared to preference rankings 

Q1            Correct              

and           answer only          

Q7            for                  

              shark  frog          

Prefer shark  6      12     18     

Prefer frog   1      2      3      

              7      14     21     

chi-square = 0.000, p = 1.000, 1 d.f. 

Q2            Correct              

and           answer only          

Q8            for                  

              birds  bflies        

Prefer birds  9      5      14     

Prefer bflies 12     3      15     

              21     8      29     

chi-square = 0.895, p = 0.344, 1 d.f.

Q3            Correct              

and           answer only          

Q9            for                  

              rcoon  evrgr         

Prefer rcoon  4      13     17     

Prefer evrgr  3      9      12     

              7      22     29     

chi-square = 0.008, p = 0.927, 1 d.f.

Q4            Correct              

and           answer only          

Q10           for                  

              seals  bats          

Prefer seals  10     9      19     

Prefer bats   4      5      9      

              14     14     28     

chi-square = 0.164, p = 0.686, 1 d.f.

Q5            Correct              

and           answer only          

Q11           for                  

              locust TB            

Prefer locust 6      6      12     

Prefer TB     12     9      21     

              18     15     22     

chi-square = 0.157, p = 0.692, 1 d.f.

Q6            Correct              

and           answer only          

Q12           for                  

              moth   lizard        

Prefer moth   4      1      5      

Prefer lizard 11     5      16     

              15     6      21     

chi-square = 0.236, p = 0.627, 1 d.f.
Because the data in the above analysis made use of only those student responses that were discrepant for parallel items, the number of samples available was considerably smaller than the size of the original pool of student responses. For this reason, paired t-test analyses were conducted. The number of correct responses for higher ranked organisms was compared to the number of correct responses for lower ranked organisms. Separate analyses were conducted for "appeal," "advancement," and "preferred" rankings. By tallying each student's correct answers according to the ranking of the organisms, the analyses were not restricted to include only discrepant responses on paired items. In other words, this type of analysis allowed the testing for the Disney effect across all six pairs of parallel items for each student.

The t-test results confirmed what had been revealed through the chi-square analysis. When correct responses on higher versus lower "appeal" organisms were compared, the mean difference was only 0.016 (t = 0.192, df = 128, p = 0.848). Comparisons of the number of correct responses on "advance" rankings also failed to be statistically significant (t = -0.491, df = 128, p = 0.624). Finally, after combining the two types of rankings into a super-category of "preference," the results were similarly unremarkable (t = -0.142, df = 128, p = 0.887).


College students enrolled in a general biology course took a two-tier test designed to assess conceptions of evolution by natural selection. Approximately 20% of students' responses were correct on only one of two parallel test items demonstrating a substantial number of students responding in a discrepant manner. It was hypothesized that the students might have responded differently on parallel items because of an intrinsic regard for the organisms depicted in the test items; this proposed factor was called the "Disney effect." The students were presented with lists of organisms and asked to rank their relative regard for the organisms. Rankings were converted to determine which organism for each pair of parallel items was preferred. Multiple statistical analyses failed to support the hypothesized existence of the Disney effect.

It is worth noting the limitations inherent in this study. While the investigation might have benefited with interviews of the students, there is no evidence that one-on-one conversations would have completely eliminated the possibility that the misunderstandings revealed through the two-tier test are attributable to semantics or language difficulties. Our confidence in the two-tier instrument is supported by the consistently high reliability coefficients associated with each administration of this test. Likewise, it would be brash to claim that the ranking task provided unequivocal data about the students' attitudes toward the organisms. At best, we were able to obtain a glimpse of their relative empathy toward organisms. Certainly we would prefer obtaining the "truth" in the college students' minds, but as all but the most deeply entrenched positivists have come to realize, objectively and absolutely measuring what people think and believe is a goal we are being forced to abandon. Nevertheless, we feel that the data and analyses presented here have the potential for shaping subsequent research and classroom practices.

The preference rankings failed to explain the discrepancies in students' responses. The data revealed that although approximately twenty percent of the responses were inconsistent (i.e., one item was correct while the other was incorrect), the rankings did not sufficiently explain the differences. The question of why one out of every five sets of responses to parallel items is not identical remains open and unanswered. At this stage, there is no clear explanation for the situation described here but this has not been a cause for discouragement. Duschl (1990) indicated that scientific knowledge is not merely a cumulative process. In reality, science is typified by "many instances of retrograde motion, stasis, and dead-end lines of inquiry. Theory building is more accurately described as an activity involving replacement and substitution than as an activity involving accretion and addition" (pp. 82-83). If we can be so bold as to suggest that this study contributes to theory about evolution education, then our findings represent a dead end, but an informative one.

For years biology educators intuited that students' religious beliefs interfere with efforts to help them learn about Darwin's theory. And even though it may appear sensible that a negative predisposition toward a science concept would serve as a barrier to students' conceptual understanding, evoluation education research has failed to support this view (cf. Bishop & Anderson, 1990). In a similar fashion, the results of this study are being offered to clarify what apparently does not influence students' response on natural selection test items. This information gives us the ability to state that "knowing what is not" is an improvement over "not knowing what is." No longer can science educators categorize students' apparent misunderstandings about natural selection as an artifact of an empathy with the organisms described in test items. This line of reasoning is no longer viable, indicating that subsequent research about how to overcome students' misconceptions about evolutionary mechanisms should be directed elsewhere.

In a subsequent study, the Understanding Biological Change test will be used before instruction on evolution to identify students who respond differentially to multiple parallel items. Those individuals will be interviewed before, during, and after the evolution instructional unit. Data from this study will allow the derivation of a more detailed picture of the development of students' understandings of evolution.


Bishop, B., & Anderson, C. W. (1990). Student conceptions of natural selection and its role in evolution. Journal of Research in Science Teaching, 27, 415-427.

Bowler, P. J. (1983). Evolution: The history of an idea. Berkeley, CA: University of California Press.

Brumby, M. (1979). Problems in learning the concept of natural selection. Journal of Biological Education, 13, 119-122.

Deadman, J. A., & Kelly, P. J. (1978). What do secondary school boys understand about evolution and heredity before they are taught the topics. Journal of Biological Education, 12, 7-15.

Demastes, S. S., Good, R. G., & Peebles, P. (1995). Students' conceptual ecologies and the process of conceptual change in evolution. Science Education, 79, 637-666.

Demastes, S. S., Good, R. G., & Peebles, P. (1996). Patterns of conceptual change in evolution. Journal of Research in Science Teaching, 33, 407-431.

Demastes, S. S., Settlage, J., & Good, R. G. (1995). Students' conceptions of natural selection and its role in evolution: Cases of replication and comparison. Journal of Research in Science Teaching, 32, 535-550.

Duschl, R. A. (1990). Restructuring science education: The importance of theories and their development. New York: Teachers College.

Gould, S. J. (1985). The flamingo's smile: Reflections in natural history. New York: W. W. Norton.

Halldén, O. (1988). The evolution of the species: Pupil perspectives and school perspectives. International Journal of Science Education, 10, 541-552.

Jensen, M. S., & Finley, F. N. (1995). Teaching evolution using historical arguments in a conceptual change strategy. Science Education, 79, 147-166.

Jensen, M. S., & Finley, F. N. (in press). Teaching evolution using historical arguments in a conceptual change strategy. Journal of Research in Science Teaching,

Jiménez, A. M. P. (1992). Thinking about theories or thinking with theories? A classroom study with natural selection. International Journal of Science Education, 14, 51-61.

Mayr, E. (1982). The growth of biological thought. Cambridge, MA: Harvard University Press.

Settlage, J., & Odom, A. L. (1995). Natural selection conceptions assessment: Development of the two-tier test "Understanding Biological Change." Paper presentation at the National Association of Research in Science Teaching annual meeting, April 1995, San Francisco, CA.

Settlage, J. (1994). Conceptions of natural selection: A snapshot of the sense-making process. Journal of Research in Science Teaching, 31, 449-457.

Tamir, P., & Zohar, A. (1991). Anthropomorphism and teleology in reasoning about biological phenomena. Journal of Biological Education, 75, 57-67.

Wandersee, J. H. (1985). Can the history of science help science educators anticipate students' misconceptions? Journal of Research in Science Teaching, 23, 581-597.


Appendix 1: The Great Chain of Being, after Charles Bonnet's mid-1700s ranking [excerpted from Bowler (1983)]. 

Highest      Man                   


Ø            Quadrupeds (Mammals)  



Ø            Birds                 

             Aquatic Birds         

             Flying Fish           

Ø            Fish                  


             Sea Serpents          

Ø            Reptiles              



Ø            Insects               



Ø            Sensitive Plants      



Ø            Herbs                 


Ø            Mold                  



Ø            Water                 


Lowest       Ethereal Matter       

Appendix 2
Understanding Biological Change, Form B
version 0.8 *
April 20, 1994
John Settlage, Jr.
1355 Rhodes Tower
Cleveland State University
Cleveland, OH 44115
216 / 687-5571

DIRECTIONS Each question on this test contains two parts. Your response to the first part involves selecting the option that best completes the phrase. These options are indicated with a 1 or a 2. The second part asks you to select the reason for the choice you made in the first part. After the word "BECAUSE"; you will find three choices marked with A, B or C. Choose the reason that best matches your understanding.

Your response to each item will consist of a two-part answer. On the blank next to each item, you are to write the number and letter that best matches your understanding of biological change.


The energy in almost every food chain can be traced back to:
1. the Sun
2. insects
A. more animals belong to this group than to any other.
B. plants absorb their energy from the soil.
C. photosynthesis is the first step in most food chains.

Explanation: The Sun is the correct answer for the first part. Even though reason A is a true statement, it is not the reason that best matches the first half of the question. Reason B seems to match with the Sun, except that soil provides minerals for plants, not energy. Therefore, the complete correct response is 1C.

Modern-day sharks can swim at speeds up to 30 knots. Suppose their ancestors swam at a much slower speed. The ability to swim fast probably:
1. developed for all the sharks in a few generations,
2. involved an increase in the percentage of sharks that can swim faster,
A. there was first a random genetic change in a few individuals.
B. the more the sharks used their muscles, the faster they became.
C. the need to catch prey caused them to swim faster.

Birds with long legs can feed in watery regions much better than can birds without long legs. If a large population of birds without long legs were transported to a remote island covered with very little dry land and lots of marshes, swamps, and ponds:
1. some birds would live and some would die,
2. the birds would gradually develop long legs,
A. all of the birds' legs would slowly change so they would be better for feeding.
B. the few birds starting out with longer legs would survive to reproduce.
C. the legs of every bird would change in the same way since they are all related.

A population of raccoons exists in an area that has had several years of very cold winters. If the winters continue to be severe in the future, we would expect that:
1. most of the raccoons will be able to live through the winter,
2. many of the raccoons will live but some will freeze to death,
A. some individuals, by chance, have thicker fur than others.
B. the raccoons will adapt to the cold weather.
C. the need to survive the cold will cause the raccoons to develop thicker fur.

Seals that live in Alaska have a fat layer. Their ancestors may not have had fat as thick as it is today. Over the centuries, changes in the seals have occurred since:
1. the need to keep warm caused the fat of every seal to get thicker,
2. more seals each generation have had thicker fat,
A. the seals wanted to adapt to their surroundings.
B. the offspring inherited a thicker layer of fat from their parents.
C. the few individuals that had a thicker fat layer lived to produce offspring.

Many years ago, the spread of locusts was controlled with the chemical DDT. Recently, chemists have found that locusts do not seem to be harmed as much by DDT. The reason for this change is that:
1. a greater number of locusts each generation are unaffected by DDT,
2. over the years, all of the locusts gradually became less affected by DDT,
A. every generation, the individual locusts who survived DDT had offspring.
B. the need to survive caused the locusts to change.
C. the use of DDT led to a mutation of the DNA in the locusts.

A population of moths contains individuals that have either light or dark colored bodies. The forest where the moths live used to have trees with both light and dark trunks. Recently, a disease has wiped out all of the types of trees except those with the darkest trunks. The effect on the moths would be that every generation:
1. the light colored moths would develop slightly darker bodies,
2. there would be a greater proportion of dark moths in the population,
A. the moths would adapt to the change in the environment.
B. the need to survive would cause the moths to shift their color.
C. only those moths with dark bodies would escape predators and live to reproduce.

Bullfrogs can jump over 10 feet in a single hop. Suppose that the bullfrogs alive today had ancestors that could not jump as far. The ability to hop large distances probably:
1. developed for all the bullfrogs in a few generations,
2. involved an increase in the percentage of bullfrogs that could hop far,
A. the more that bullfrogs used their muscles, the further they could jump.
B. there was first a random genetic change in a few individuals.
C. the need to avoid predators caused them to jump further.

Butterflies with a long proboscis (feeding tube) can reach the nectar at the base of flowers better than can butterflies with shorter proboscis. Some flowers have shallow tubes with nectar at the bottom while other flowers have much deeper and narrower tubes. If a large population of butterflies with short proboscises were transported to a desert oasis covered entirely with plants whose flowers had very long tubes:
1. some butterflies would live and some would die,
2. the butterflies would gradually develop longer proboscises,
A. the few butterflies starting out with longer proboscises would survive to reproduce.
B. the proboscis of every butterfly would change in the same way since they are all related.
C. all of the butterflies' proboscises would slowly change so they would be better for reaching the nectar.

A population of evergreens exists in an area that has had several years of very hot and dry summers. If the summers continue to be severe in the future, we would expect that:
1. many of the evergreens will live but some will die because of the dryness,
2. most of the evergreens will be able to live through the summer,
A. the need to survive the summers will cause the evergreens to develop better ways to avoid drying out.
B. some individual evergreens have, by chance, better ways of conserving water.
C. the plants will adapt to the hot and dry weather.

Bats that feed at night have a very sophisticated sense of hearing. Their ancestors may not have heard as well as bats of today. Over the centuries, changes in the bats have occurred since:
1. the need to feed at night caused the hearing sense of every bat to increase,
2. more bats each generation have had better hearing,
A. the bats wanted to adapt to their surroundings.
B. the offspring inherited better hearing from their parents.
C. the few individuals that had better hearing lived to produce offspring.

Tuberculosis (TB) bacteria
Many years ago, bacteria that caused TB were controlled with a combination of three antibiotics. Recently, doctors have found that TB bacteria do not seem to be harmed as much by the three antibiotics. The reason for this change is that:
1. over the years, all of the bacteria gradually became less affected by penicillin,
2. a greater proportion of bacteria are unaffected by the penicillin each generation,
A. the need to survive caused the bacteria to change.
B. the use of antibiotics led to a mutation of the DNA in the bacteria.
C. every generation, the individual bacteria that survived the antibiotics reproduced.

A population of lizards contains individuals that have either solid green or green-striped bodies. The region where the lizards live used to have grass plants with both solid green and green-striped leaves. Recently, a disease has wiped out all of the types of grass except those with the solid green leaves. The effect on the lizards would be that every generation:
1. the green-striped lizards would develop slightly less striped bodies,
2. there would be a greater proportion of individuals with solid green bodies,
A. only those lizards with solid green bodies would escape predators and live to reproduce.
B. the lizards would adapt to the change in the environment.
C. the need to survive would cause lizards to change their body color.

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