Lecture_8_comparative UPPER LIMB

Overview of the Upper Limb

  • Presented by: A/Prof. Michael Knapp, Slides by Dr. Charlotte King

Today's Plan

  • Explore differences between human and great ape upper limbs:

    • Shoulder

    • Wrist

    • Hand

  • Discuss evolutionary significance of these differences

Characteristics of the Human Upper Limb

  • Flexible, Strong, Precise

  • Capable of complex tasks

Key Differences between Human and Great Ape Upper Limbs

  • Main Factors

    • Differences in locomotion

    • Adaptation for precision grip (tool use)

Locomotion in Apes

  • Brachiation:

    • Gibbons: true brachiators

    • Other great apes (chimpanzees, gorillas, orangutans): modified brachiators

Quadrupedal Locomotion

  • Chimpanzees, gorillas, orangutans:

    • Use ground locomotion

    • Chimpanzees and gorillas: knuckle-walkers

    • Orangutans: fist-walkers

Bipedalism

  • Humans:

    • Only habitually bipedal ape

    • Upper limb freed for manipulation

Shoulder Adaptations in Apes

  • Mobility Needs

    • Brachiators require mobile shoulder joints

  • Features:

    • Globular humeral head

    • Shallow glenoid fossa

Issues with Brachiator’s Shoulder

  • Mobility vs. Stability:

    • Common shoulder dislocations

    • Rotator cuff issues

Adjustments to Brachiator’s Shoulder

  • Differences include:

    • Longer, narrower scapula

    • Adaptations for hanging

    • Glenoid fossa orientation helps in hanging vs. energy storage in humans

Adaptations in the Wrist

  • Increased wrist mobility:

    • Meniscus helps in motion

    • Ulna adjustment for enhanced range

Limb Proportions

  • Arboreal apes: longer arms than legs

  • Humans: shorter forearms for effective hand positioning

Hand Adaptations

  • Adaptations for knuckle-walking in apes:

    • Ridges on metacarpal heads

    • Extended distal radial surface

    • Fused carpals for stability

  • Human Advantages:

    • Shorter, straighter fingers

    • Larger thumbs for manipulation

Grip and Hand Adaptations

  • Humans exhibit two grips:

    • Power grip: Whole palm engagement

    • Precision grip: Opposition of fingers and thumb (fingertips)

Power vs. Precision Grip

  • Power Grip:

    • Symmetrical wrap around objects

    • Similar to ape hook grip

  • Precision Grip:

    • Fine control via intrinsic hand muscles

    • Larger, complex thenar muscles involved

Saddle Joints

  • Allow thumb rotation

Reasons Behind Human Precision Grip

  • Wider fingers with larger surface area

  • Unique proportion and shape allowing enhanced grip

Evolutionary Development

  • Gradual changes in hand structure over millions of years

    • Finger curvature and thumb proportions

  • Mosaic evolution: combining ape-like and human features in hominins

Functional Importance of Grip Evolution

  • Adaptations for improved tool use in human evolution

  • Indicate behaviors not limited to Homo species (e.g., in Australopithecus)

Summary

  • Upper limb adaptations linked to locomotion and hand usage

  • Evidence of arboreal constraints in human anatomy

  • Variations in the hand reflect complex movement capabilities

Further Reading

  • Tocheri et al. (2008) on hominin hand evolution

  • Kivell et al. (2015) studying primate hand evolution.