One theory behind human bipedalism speculates that it originated in a mostly ground-based ancestor that practiced four-legged 'knuckle-walking,' like ...
GMAT Information and Ideas : (Ideas) Questions
One theory behind human bipedalism speculates that it originated in a mostly ground-based ancestor that practiced four-legged 'knuckle-walking,' like chimpanzees and gorillas do today, and eventually evolved into moving upright on two legs. But recently, researchers observed orangutans, another relative of humans, standing on two legs on tree branches and using their arms for balance while they reached for fruits. These observations may suggest that ______
Which choice most logically completes the text?
bipedalism evolved because it was advantageous to a tree-dwelling ancestor of humans.
bipedalism must have evolved simultaneously with knuckle-walking and tree-climbing.
moving between the ground and the trees would have been difficult without bipedalism.
a knuckle-walking human ancestor could have easily moved bipedally in trees.
Step 1: Decode and Map the Passage
Part A: Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "One theory behind human bipedalism speculates that it originated in a mostly ground-based ancestor that practiced four-legged 'knuckle-walking,' like chimpanzees and gorillas do today, and eventually evolved into moving upright on two legs." |
|
| "But recently, researchers observed orangutans, another relative of humans, standing on two legs on tree branches and using their arms for balance while they reached for fruits." |
|
| "These observations may suggest that ______" |
|
Part B: Provide Passage Architecture & Core Elements
Main Point: New observations of tree-dwelling orangutans using bipedalism may challenge the ground-based theory of how human bipedalism evolved.
Argument Flow: The passage presents one established theory about bipedalism originating in ground-dwelling knuckle-walkers, then introduces recent observations of orangutans being bipedal in trees, setting up a contrast that leads to a new possible conclusion about bipedalism's origins.
Step 2: Interpret the Question Precisely
This is a fill-in-the-blank question asking us to choose the best logical connector. The answer must create the right relationship between what comes before and after the blank.
Step 3: Prethink the Answer
- The orangutan observations show our close relatives being bipedal in trees, which contrasts with the ground-based knuckle-walking theory
- This new evidence suggests that bipedalism might have evolved differently than previously thought - perhaps it was useful for tree-dwelling ancestors rather than ground-dwelling ones
bipedalism evolved because it was advantageous to a tree-dwelling ancestor of humans.
✓ Correct
- This directly connects the orangutan observations to an alternative origin theory
- Matches our prethinking that tree-dwelling behavior could explain bipedalism evolution
bipedalism must have evolved simultaneously with knuckle-walking and tree-climbing.
✗ Incorrect
- Claims simultaneous evolution of different locomotion types
- The passage doesn't suggest these evolved at the same time
moving between the ground and the trees would have been difficult without bipedalism.
✗ Incorrect
- Focuses on difficulty of moving between environments
- The orangutan observations don't suggest this
a knuckle-walking human ancestor could have easily moved bipedally in trees.
✗ Incorrect
- Tries to reconcile knuckle-walking ancestors with tree bipedalism
- Misses the point that the orangutan evidence suggests an alternative to the knuckle-walking theory