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Item CA041002: Similar skeletal features in organisms (chimpanzees and gorillas) indicate a common ancestor.

A class of students is visiting the primate room of a natural history museum. Some of the students are looking at the skeleton of a chimpanzee next to the skeleton of a gorilla.

 A sign next to the skeletons reads:

“Do chimpanzees and gorillas share a common ancestor?”

The teacher asks the students to think about that question and then to write an argument to justify their answer. This is what one of the students writes:

Common ancestors are a topic in evolution. Similar skeletal features likely indicate a common ancestor.  Chimpanzees and gorillas have similar anatomical features. For example, chimpanzees and gorillas both have opposable thumbs and their ribcages are very similar. Chimpanzees and gorillas may have a common ancestor.

Identify the claim, evidence, and reasoning statement in the student’s argument.

  1. Claim: Similar skeletal features likely indicate a common ancestor.

    Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

    Reasoning: Chimpanzees and gorillas have similar skeletal features.

  2. Claim: Similar skeletal features likely indicate a common ancestor.

    Evidence: Chimpanzees and gorillas have similar skeletal features.

    Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

  3. Claim: Chimpanzees and gorillas may have a common ancestor.

    Evidence: Similar skeletal features likely indicate a common ancestor.

    Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

  4. Claim: Chimpanzees and gorillas may have a common ancestor.

    Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

    Reasoning: Similar skeletal features likely indicate a common ancestor.

Pre-Test

Distribution of responses (prior to studying evolution in high school)
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 580
6–8
n = 25
9–12
n = 514
Male
n = 254
Female
n = 286
English
n = 526
Other
n = 13
A.

Claim: Similar skeletal features likely indicate a common ancestor.

Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

Reasoning: Chimpanzees and gorillas have similar skeletal features.

20% 28% 19% 20% 18% 19% 23%
B.

Claim: Similar skeletal features likely indicate a common ancestor.

Evidence: Chimpanzees and gorillas have similar skeletal features.

Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

19% 16% 19% 22% 16% 19% 23%
C.

Claim: Chimpanzees and gorillas may have a common ancestor.

Evidence: Similar skeletal features likely indicate a common ancestor.

Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

23% 28% 22% 26% 20% 23% 23%
D.

Claim: Chimpanzees and gorillas may have a common ancestor.

Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

Reasoning: Similar skeletal features likely indicate a common ancestor.

39% 28% 40% 32% 46% 39% 31%

Post-Test (Control)

Distribution of responses (following typical high school instruction on evolution)
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 255
6–8
n = 15
9–12
n = 195
Male
n = 97
Female
n = 119
English
n = 205
Other
n = 6
A.

Claim: Similar skeletal features likely indicate a common ancestor.

Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

Reasoning: Chimpanzees and gorillas have similar skeletal features.

18% 47% 16% 22% 16% 17% 67%
B.

Claim: Similar skeletal features likely indicate a common ancestor.

Evidence: Chimpanzees and gorillas have similar skeletal features.

Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

14% 0% 14% 19% 9% 14% 17%
C.

Claim: Chimpanzees and gorillas may have a common ancestor.

Evidence: Similar skeletal features likely indicate a common ancestor.

Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

19% 13% 20% 18% 20% 19% 0%
D.

Claim: Chimpanzees and gorillas may have a common ancestor.

Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

Reasoning: Similar skeletal features likely indicate a common ancestor.

49% 40% 49% 42% 55% 50% 17%

Post-Test (Treatment)

Distribution of responses (following completion of an evolution curriculum module)
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 301
6–8
n = 8
9–12
n = 274
Male
n = 134
Female
n = 150
English
n = 274
Other
n = 9
A.

Claim: Similar skeletal features likely indicate a common ancestor.

Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

Reasoning: Chimpanzees and gorillas have similar skeletal features.

18% 0% 19% 14% 21% 18% 22%
B.

Claim: Similar skeletal features likely indicate a common ancestor.

Evidence: Chimpanzees and gorillas have similar skeletal features.

Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

14% 13% 15% 19% 11% 15% 0%
C.

Claim: Chimpanzees and gorillas may have a common ancestor.

Evidence: Similar skeletal features likely indicate a common ancestor.

Reasoning: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

22% 25% 22% 23% 21% 22% 22%
D.

Claim: Chimpanzees and gorillas may have a common ancestor.

Evidence: Chimpanzees and gorillas both have opposable thumbs and similar ribcages.

Reasoning: Similar skeletal features likely indicate a common ancestor.

46% 63% 45% 44% 47% 45% 56%