Revision summary
Erect posture frees the hands for tools and carrying. It favours endurance walking and a high visual field. Costs include lumbar strain, difficult birth, and venous problems. The obstetric dilemma pits a narrow pelvis against a large brain. Selection kept the bargain because making and ranging paid.
Model answer
Introduction
Bipedal erect posture is the hominin hallmark. It freed the hands and strained the spine, pelvis, and birth canal. Gains and losses are one design.
Body
Gains
- Hands free for tools, carrying, and gesture. Washburn and Darwin already tied bipedalism to culture.
- A high, scanning eye-line and endurance walking, later used by Homo erectus on open landscapes.
- Thermoregulation in savanna sun is argued: less surface to noon radiation, more sweating skin.
Losses
- Lumbar lordosis, slipped discs, and osteoarthritis of the lower back and knees.
- A narrow pelvic inlet versus a large neonatal brain: the obstetric dilemma, with rotational birth and risk to mother and child.
- Inguinal hernia, varicose veins, and haemorrhoids from vertical viscera and valves.
- Foot arches and fallen arches; a locked knee that saves energy but fails in injury.
Balance
- Natural selection kept the posture because foraging and making paid more than a perfect back.
Flow diagram
flowchart TD BP[Bipedalism] --> G[Hands tools endurance] BP --> L[Spine pelvis veins feet] L --> OB[Obstetric dilemma]
Conclusion
Erect posture bought tools, range, and a scanning stance. It cost backs, births, and veins. The human body is that bargain.
Quick related
Students also ask
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Explain the skeletal changes due to erect posture and their implications.
Next question on this syllabus topic (2016 · Q8(c)). View answer →
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Was bipedalism for running first?
Early hominins walk. Endurance running is clearer later, with erectus-grade bodies.
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Can culture remove the losses?
Midwifery, chairs, and surgery mitigate. They do not rewrite the skeleton.
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