Before You Begin
Question #47402
The Question
During hominid evolution, the transition to efficient bipedalism necessitated a restructuring of the pelvic girdle. Concurrently, the genus Homo experienced a rapid increase in cranial capacity. Which of the following represents the primary evolutionary compromise (often termed the 'obstetrical dilemma') resulting from these two conflicting structural demands?
Options
- A.
Maintenance of a narrow, bowl-shaped pelvis for bipedal efficiency, resulting in the birth of neurologically immature infants to accommodate the restricted birth canal.
- B.
Continuous lateral expansion of the coxal bones in later Homo species to fully accommodate the increasing fetal cranial capacity prior to birth.
- C.
Premature ossification of fetal cranial sutures in utero to withstand the mechanical stress of the restructured bipedal pelvic inlet.
- D.
Prolongation of the gestation period to ensure complete encephalization and motor development before navigating the narrow pelvic girdle.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Appendicular Girdle|Hominid Cranial Capacity|Foramen Magnum
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often assume evolution perfectly adapts all structures simultaneously without constraints.
The trap lies in failing to recognize evolutionary trade-offs.
A student might logically guess that the pelvis simply widened to accommodate the brain (Option B) or that gestation lengthened to support a bigger brain (Option D), missing the strict biomechanical constraints of bipedalism taught in Locomotion & Movement.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Locomotion and Movement - Class 11 |
| Concept | Appendicular Girdle Mechanics |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |