UNIT 10 COMPARATIVE ANATOMY OF HUMAN AND NONHUMAN PRIMATES REVISION NOTES

 Primate Behaviour and Adaptations

Introduction:

• Triangular Model of Primate Adaptation:

  • Behaviour: Influences and is influenced by anatomy and environment.
  • Anatomy: Affected by evolutionary history and determines behavioural capabilities.
  • Environment: Shapes anatomy and behaviour.

• Evolutionary History:

  • Affects behaviour, anatomy, and the environment's impact on them.
  • Example: Human body adaptations for bipedalism and arm-swinging from ancestral past.

Key Concepts:

• Behavioural Ecology: How primates use their environment, affecting their anatomy and evolution.
• Evolutionary History: Provides context for understanding current survival abilities and morphological changes.
• Mosaic Structures: Reflect both evolutionary history and current survival adaptations.

Adaptations and Niche:

• Adaptation: Characteristics that allow an organism to survive and reproduce.
• Niche: The way an organism makes a living, finding resources to survive and compete.
• Adaptive Radiation: Evolution of a single group into various forms to exploit different ecological niches.

Key Points:

1. Behaviour:

   • Determines movement and interaction with the environment.
   • Example: Locomotion abilities influencing habitat use.

2. Anatomy:

   • Reflects evolutionary adaptations for survival in specific environments.
   • Example: Human hips and legs for bipedalism, upper body for arm-swinging.

3. Environment:

• Influences and is influenced by behavioural patterns and anatomical structures.
• Example: Arboreal environment shaping primate adaptations for climbing and brachiation.

Adaptive Radiation:

• Definition: Evolution of diverse species from a common ancestor to exploit different niches.
• Importance: Central to understanding biological diversity and evolution.

Study of Primates:

• Purpose: Understanding adaptations to comprehend survival abilities and evolutionary history.
• Implications: Helps sequence morphological changes and explain primate phylogeny.

Primate Evolutionary Trends

Introduction

Primate evolutionary trends provide a comparative understanding of the anatomy and behavior of human and non-human primates. These trends highlight shared common characteristics rather than progress and reflect adaptations to environmental challenges.

General Trends:

• Generalized Structure:
  • Primates are less specialized compared to other mammals.
  • Retain versatile anatomical features without extreme specialization.

1. Limbs and Locomotion

• Retention of Five Digits:
  • Pentadactyl limbs (five digits on hands and feet).
• Nails Instead of Claws:
  • Provides better manipulation abilities.
• Flexible Hands and Feet:
  • High degree of prehensility (grasping ability).
• Erect Posture:
  • Particularly in the upper body.
• Retention of Clavicle:
  • Maintains shoulder mobility and stability.

2. Teeth and Diet

• Generalized Dental Pattern:
  • Especially in molars, allowing a varied diet.
• Lack of Specialization in Diet:
  • Correlated with the generalized dental structure.

3. Senses, Brain, and Behavior

• Reduction of Snout:
  • Proportionate reduction in olfactory (smell) brain areas.
• Increased Emphasis on Vision:
  • Elaborate visual brain areas; reduced reliance on smell.
  • Color vision likely present in most primates.
• Brain Expansion and Complexity:
  • Larger, more complex brains.
• Efficient Foetal Nourishment:
  • Longer gestation, single births are common.
• Extended Life Span:
  • Longer periods of infancy and overall lifespan.
• Dependency on Learned Behavior:
  • Longer infant and child dependency periods.
  • Increased parental investment in fewer offspring.
• Permanent Adult Male Association:
• Males often remain with the group permanently.

MORPHOLOGICALAND ANATOMICAL FEATURES OF APES 

Apes Overview

• Native Regions: Africa and Southeast Asia
• Anthropoid Primates: Apes are part of this group.
• Traditional Exclusion: Apes are traditionally differentiated from humans.
• Locomotion: Key factor differentiating apes from other primates.
• Branches/Super Families:
• Hominoidea: Gibbons (lesser apes)
• Hominids: Great apes

Characteristics of Apes

• No Tail: Apes do not have tails.
• Teeth: Apes and humans have five cusps on their molars (Y-5 pattern), unlike monkeys which have four cusps.
• Locomotion: Apes move using various methods including tree-swinging and knuckle-walking on the ground (quadrupedal movement).
• Arm and Limb Ratio: Apes have longer arms compared to their hind limbs.
• Rib Cage: Apes have rib cages that are flattened from front to back.
• Brain Size: Apes have larger brains than monkeys, enabling them to learn complex behaviors.
• Facial Expression: The upper lip is free from the gums, allowing for mobile and expressive faces, facilitating communication through facial expressions.

Gibbons: Characteristics

• Size: Smallest of the apes, with the largest weighing up to 10.5 kg.
• Habitat: Dense tropical forests of Southeast Asia.
• Locomotion:
  • Acrobatic brachiators 75% of the time.
  • Move quadrupedally or bipedally the remaining 25% of the time.
• Sexual Dimorphism: None.
• Hair Coverage: Face and ischial callosities are hairless.
• Digital Formula: 3>2>4>5>1.
• Digits: All except the thumb have nails.

Orangutans: Characteristics

• Habitat: Thick tropical rain forests in Sumatra and Borneo.
• Diet: Primarily fruit eaters.
• Appearance: Reddish hair coating on the body.
• Locomotion:
  • Brachiate and often hang by their very long arms.
  • Have long, curved hands.
  • Too heavy to swing between trees, often knuckle-walk on the ground to move between trees.
• Social Structure: Live in small groups of 2-4 members.
• Sleeping Habits: Make a new nest each night to sleep in.
• Digital Formula: 3>4>2>5>1.
• Digits: Short thumb, long other fingers with flat nails.

Chimpanzees: Characteristics

• Habitat: Forest fringe and open woodland in Africa.
• Locomotion:
  • Knuckle-walk on the ground and in trees.
  • Brachiate and can walk on two legs.
• Diet: Mainly fruit, supplemented by insects like termites; meat is rarely eaten but greatly relished.
• Senses: Highly developed visual sense; individuals are recognized by facial features.
• Social Structure:
  • Live in troops of about 20 animals.
  • Offspring stay with their mothers for 4-5 years, learning complex behaviors.
• Intelligence:
• Capable of fashioning tools from sticks.
• Can throw stones when frightened and use sticks for defense.

Gorillas: Characteristics

• Habitat: Africa
• Lifestyle:
  • Forest dwellers, spending most of their lives on the forest floor.
• Diet: Primarily celery, leaves, and shoots, rather than fruit.
• Movement: Nomadic, traveling daily to new feeding areas in groups of about 12-20 animals.
• Sexual Dimorphism: Males are larger and have large canine teeth.
• Behavior:
• Make nests each night.
• Forelimbs are considerably longer than hind limbs.

COMPARISON OF MORPHOLOGICAL AND ANATOMICAL FEATURES OF MAN AND APES

Ape Skull:

• Structure:
  • Rounded brain case for brain protection and muscle attachment.
  • Foramen magnum located towards the rear, requiring strong neck muscles.
  • Large nuchal crest for neck muscle attachment.
• Specific Features:
  • Large mandible with no prominent chin.
  • Prominent snout/muzzle.
  • Massive zygomatic arch with a gap for jaw muscle passage.
  • Large sagittal crest for strong jaw muscle attachment.
  • Receding forehead with large brow ridges.
  • Smaller cranium capacity.

Human Skull:

• Structure:
  • Balanced foramen magnum towards the center of the skull.
  • Requires less muscular effort to support the head.
• Specific Features:
• Small mandible with a prominent chin.
• No sagittal crest and reduced jaw muscles.
• Vertical face without a snout/muzzle.
• No brow ridges and a vertical forehead.
• Large brain size, particularly in the frontal and occipital regions.
• Associated with increased reliance on vision, advanced thinking, and speech.

Teeth and Jaws: Ape vs. Human

Ape Teeth and Jaws:

• Teeth Characteristics:
  • Large teeth with thick enamel, especially molars.
  • Noticeable size difference between incisors and canines.
  • U-shaped dental arcade.
  • Lower jaw protrudes due to large teeth and thick enamel.
• General Features:
  • Sloping face due to protruding lower jaw.
  • Upper teeth arranged in a U-shaped dental arcade.

Human Teeth and Jaws:

• Teeth Characteristics:
  • Smaller teeth with reduced enamel thickness.
  • Reduced size difference between incisors and canines.
  • Parabolic (bow-shaped) dental arcade.
  • No diastema (gap) between upper canine and first premolar.
• General Features:
• Flatter face due to reduced size of lower jaw.
• Upper teeth arranged in a parabolic (bow-shaped) dental arcade.

Ape Backbone:

• Single gentle curve.
• Weight distribution is not directly above the hip joints.

Human Backbone:

• 'S' shaped curvature.
• Enables weight to be carried nearly directly above the hip joints.

Quadrupedal Mammals (Apes):

• Long hip bone.
• Supports quadrupedal locomotion.

Humans:

• Hip bone forms a bowl-shaped support for abdominal organs.
• Reduced height and brings the sacroiliac joint close to the hip joint.

Apes:

• Not knock-kneed.
• Each knee is not directly underneath the center of the hip girdle.
• Sway from side to side when attempting to walk on two legs to avoid falling over.

Humans:

• Knock-kneed.
• Each knee is almost directly underneath the center of the hip girdle.
• Larger "carrying angle" or valgus angle.
• Allows the leg to be closer to the body's center of gravity, reducing the tendency to lose balance when one foot is lifted off the ground.

Humans:

• Foot primarily supports and transmits body weight, acts as a locomotor organ.
• Great toe (hallux) is non-opposable, largest digit, aligned with other toes.
• Lateral toes are reduced in size, fifth toe (little toe) is very small.
• First or second digit is the longest.
• Dorsal and ventral surfaces of all digits are aligned, ventral surfaces face downward.
• First metatarsal included in common transverse metatarsal ligament.
• Metatarsals of all digits are incorporated into the foot tissue.
• First metatarsal has a flattened area at its posterior for articulation with cuneiform bone.

Apes:

• Foot acts as both a grasping organ and a locomotor organ.
• Great toe is opposable, not well-developed, not aligned with other digits.
• Lateral toes are well-developed.
• Third digit is the longest.
• Ventral surface of the great toe does not face downward laterally.
• First metatarsal is not included in the common transverse metatarsal ligament.
• Great toe is free from the common covering.
• Articular region of the cuneiform bone is convex, and that of the metatarsal is concave.

Comparison of Femur between Man and Gibbon:

General Form and Arrangement:

• Man:
  • Femur is comparatively stout and not as long.
  • Shaft is slightly curved, presenting three surfaces and three borders, resulting in a non-circular cross-section.
• Gibbon:
  • Femur is long, slender, with a straight and cylindrical shaft, showing a more or less circular cross-section.

Upper Extremity:

• Man:

  • Neck of femur forms a more obtuse angle with the shaft.
  • Lesser trochanter is placed posteriorly.

• Gibbon:

  • Neck of femur is short, stout, forms a less obtuse angle with the shaft.
  • Lesser trochanter is placed postero-medially.

Shaft:

• Man:

  • Linea aspera is well-developed, forming a distinct ridge.
  • Popliteal area is well-marked, convex from side to side and above to downwards.

• Gibbon:

  • Linea aspera is faintly developed.
  • Popliteal area is convex from side to side but straight from above to downwards.

Lower Extremity:

• Man:

  • Medial condyle is larger than the lateral condyle.
  • Medial condyle extends below the level of the lateral condyle.

• Gibbon:

• Two condyles are almost equal in size.
• Medial condyle does not extend below the level of the lateral condyle.

Comparison of Hands between Humans and Apes:

Human Hand:

• Thumb:
  • Relatively longer compared to apes.
  • Connected to the wrist by a saddle joint.
  • Allows the thumb to oppose and touch the tip of any finger, enabling precision grip.
• Phalanges (Fingers):
  • Straight shape.
  • Facilitates fine manipulative movements and precision grip.
• Grips:
  • Capable of both power grip (grasping objects with entire hand) and precision grip (grasping small objects between fingers and thumb).

Ape Hand:

• Thumb:
  • Typically shorter than in humans.
  • Not as mobile due to different joint structure.
• Phalanges (Fingers):
  • Curved shape.
  • Adapted for grasping branches during brachiation (swinging from tree to tree).

General Comparison:

• Functionality:
• All primates, including humans, can perform a power grip.
• Humans uniquely capable of a precision grip, allowing for intricate and fine manipulations.

Comparison of Human and Ape Characteristics:

Chest:

• Human chest is flatter from front to back compared to apes.
• This alignment concentrates body weight closer to the spine.

Shoulder:

• Humans have a longer clavicle (collar bone) than apes.
• Scapula (shoulder blade) in humans is positioned on the back, unlike in quadrupeds where it's on the sides of the chest.

Skin:

• Humans have as many hairs per square centimeter of skin as chimpanzees.
• Human hair is finer and shorter, giving the impression of nakedness compared to apes.
• Humans have a higher density of sweat glands compared to apes.

SUMMARY OF SIMILARITIES AND DIFFERENCES BETWEEN CHIMPANZEES, AUSTRALOPITHS AND MODERN HUMANS AS A RESULT OF MILLIONS OF YEARS OF EVOLUTION

Relation of Anatomy and Posture in Primates:

• Siamang Example:

  • Ability to hang by arms and legs crucial for feeding from small branches.
  • Hanging posture influences anatomy to support feeding behaviors.

• Marmoset Example:

  • Hand structure adapted for holding and processing food, as well as grasping supports during movement.
  • Anatomy reflects dual function of feeding and locomotion needs.

• Reconstructing Behavior from Anatomy:

  • Primate anatomy linked to locomotion and posture helps reconstruct behaviors of fossil species.
  • Details of anatomy provide insights into how extinct species moved and interacted with their environment.

• Diversity in Locomotion:

• Various primate species exhibit different locomotion methods:
• Some leap, others are arboreal quadrupeds.
• Some swing by their arms, while one species, humans, are bipedal.

Anatomy and Movement in Primates:

• Field Studies Insight:

  • Field observations reveal species-specific movements and their ecological contexts.
  • Primates exhibit versatility in movement, including leaping, quadrupedal running, and suspending themselves from branches.

• Complex Relationship:

  • Anatomy is intricately linked to various types of movement.
  • Primate anatomy reflects compromises to accommodate multiple locomotor behaviors.

• Muscles and Bones Reflect Locomotor Differences:

  • Differences in locomotion frequency among primate species are mirrored in their muscular and skeletal anatomy.
  • Example: Two closely related Presbytis species in Malaysia differ in anatomy; one leaps about 20% more frequently than the other.