11A/B PP - Classification & Bipedalism

Classification of Homo sapiens

Animalia → Chordata → Vertebrata → Mammalia → Primates → Hominoidea → Hominidae → Hominini → Homo → sapiens

What defines Kingdom Animalia?

Organisms are:

• Multicellular

• Eukaryotic

• Lack cell walls

What defines Chordata and Vertebrata?

Chordata: possess a rod-like support structure.

Vertebrata: possess a vertebral column (backbone)

What defines Mammalia?

Mammals have:

• Mammary glands that produce milk

• Hair or fur

Characteristics of primates

Primates have:

• Stereoscopic 3D colour vision

• Prehensile hands with opposable thumbs

• Large brains relative to body size

• Nails instead of claws

Characteristics of hominoids (Hominoidea)

Hominoids include great apes and lesser apes (gibbons).

They have:

• Distinctive molar teeth

• Broad rib cage and pelvis

• Shorter spine between rib cage and pelvis

• No tail

Most have longer arms than legs, except humans.

Characteristics of hominids (Hominidae)

Hominids:

• Include the great apes

• Have larger brains than other primates

• Have flatter faces

• Display a more upright posture

Characteristics of hominins (Hominini)

Hominins are characterised by:

• Bipedalism

• A large cerebral cortex

Examples include:

• Ardipithecus

• Australopithecus

• Homo

Characteristics of Homo and Homo sapiens

• Reduced tooth size

• Recognisably human

Homo sapiens

• High forehead

• Well-developed chin

• Thin skull bones

What is the foramen magnum?

The foramen magnum is the hole at the base of the skull where the spinal cord connects to the brain.

How does the foramen magnum provide evidence for bipedalism?

A foramen magnum positioned toward the back of the skull is associated with quadrupedal movement.

A more central position supports upright posture and bipedal walking.

Over time, the foramen magnum became more central in hominins.

How did the pelvis change in hominins?

Human pelvises are:

• Shorter

• Shallower

• More bowl-shaped

The bowl-shaped pelvis helps support the upper body during upright walking

What is the significance of angled femurs?

Human femurs angle inward toward the knees.

This places the foot more directly beneath the body and improves stability when walking upright.

How is the human foot adapted for bipedalism?

Humans have:

• A big toe aligned with the other toes

• No prehensile foot

• Two arches

• A wide heel

The foot is adapted for propulsion and efficient walking rather than climbing or grasping

How did the spine change during hominin evolution?

Apes have a C-shaped spine.

Humans have an S-shaped spine with upper and lower curves that:

• Support body weight vertically

• Assist upright movement

How did the arm-to-leg ratio change?

Apes and earlier hominins generally had longer arms relative to legs.

Humans have:

• Longer legs

• Shorter arms

Longer legs improve the efficiency of long-distance walking.

Advantages of bipedalism

Bipedalism allowed:

• Carrying offspring

• Carrying food

• Efficient long-distance movement

• Better thermoregulation

• Seeing above long grass

Tool use was likely a consequence of bipedalism rather than its original cause.

How does bipedalism improve thermoregulation?

Walking upright:

• Exposes less surface area to direct sunlight

• Increases airflow across the body

These factors improve cooling.

How did hominin hands evolve?

Humans have:

• Shorter, straighter fingers

• Longer thumbs relative to fingers

These features improve manipulative control.

What is a precision grip?

The precision grip allows fine manipulation of objects using the thumb and fingers.

It is possible because humans have opposable thumbs and highly dexterous hands.

Why were changes in hand anatomy important?

Improved hand and wrist control enabled:

• Manipulation of objects

• Tool use

• Development of hunting equipment

These adaptations contributed to human success

Power grip vs precision grip

The opposable thumb enables both:

• Precision grip for delicate tasks

• Power grip for strength and forceful holding

Both were important for tool use and survival

Mammals

• three middle ear bones

• single lower jaw bone

• mammary glands

• variety of teeth

• hari/fur

Primates

• flexible spines and hip rotation

• prehensible hands and/or feet

• binocular colour 3D vision

• opposable thumb/big toe

• sensitive touch receptors

Hominoids

• Y5- shaped molar teeth

• broad rib cage

• large cranium

• no tail

Hominins

• bipedalism

• structural consequences of bipedalism- centralised foramen magnum, S-shapes spine, broader rib cage, bowl-shaped pelvis, increasing carrying angle of the femur

• communication and formation of complex social groups