Bipedalism

Bipedalism

Bipedalism - on two feet.

•The single most distinctive feature

of Hominids

•Hominid bipedalism is habitual and

required

Body Changes: knuckle

walkers vs. bipedalists

Body Changes: knuckle

walkers vs. bipedalists

foramen magnum

Circular hole at the bottom

of the skull where the

medulla oblongata (spinal

cord) enters and exits the

skull

The foramen magnum is

farther underneath the

skull, so the head is more

or less balanced on the

spine.

Body Changes: knuckle

walkers vs. bipedalists

spine

The spine has two

distinctive curves—a

backward (thoracic) one

and a forward (lumbar)

one—that keep the body

and weight centered

above the pelvis.

Body Changes: knuckle

walkers vs. bipedalists

pelvis

The pelvis is shaped

more in the form of a

bowl to support internal

organs.

Body Changes: knuckle walkers

vs. bipedalists

Hip bones

The hip bones are

shorter and broader,

stabilizing weight

transmission.

a) Homo sapiens.

(b) Early hominid (Australopithecus) from South Africa.

(c) Chimpanzee. Note especially the length and breath of the iliac blade and the line of weight

transmission (shown in red).

Body Changes: knuckle walkers

vs. bipedalists

Hip bones

Muscle attachment

ridges on the pelvis

become heavier.

Body Changes: knuckle walkers

vs. bipedalists

Body Changes: knuckle walkers

vs. bipedalists

legs

Lower limbs are

longer.

In humans the thigh

comprises 20% of

body height, while in

gorillas it comprises

only 11%.

Body Changes: knuckle walkers

vs. bipedalists

20 %11 %

of body height

Body Changes: knuckle walkers

vs. bipedalists

Leg muscle

structures

change

Body Changes: knuckle walkers

vs. bipedalists

Body Changes: knuckle walkers

vs. bipedalists

Body Changes: knuckle walkers

vs. bipedalists

Femur and knee action

The femur is angled

inward, keeping the legs

more directly under the

body.

Modified knee anatomy

also permits full extension

of this joint.

Body Changes: knuckle walkers

vs. bipedalists

Body Changes: knuckle walkers

vs. bipedalists

feet

The big toe is enlarged and

brought in line with the

other toes

An arch forms, helping

absorb shock and adding

propulsive spring.

Body Changes: knuckle walkers

vs. bipedalists

gibbons

gibbons

orangutans

orangutans

bonobos

bonobos

chimps

chimps

gorillas

gorillas

humans

humans

Body Changes: knuckle walkers

vs. bipedalists

.

Foot (pedal) anatomy

Understanding Physical Anthropology and Archaeology, 9th ed., p. 435

Body Changes: knuckle walkers

vs. bipedalists

Foot (pedal) anatomy

Understanding Physical Anthropology and Archaeology, 9th ed., p. 436

Body Changes: knuckle walkers

vs. bipedalists

Opposable thumb

Capable of bending in such

a way that it can touch all

the other digits on the hand

Body Changes: knuckle walkers

vs. bipedalists

Opposable thumb

Large role in the ancient

humans inventing and

using tools

Body Changes: knuckle walkers

vs. bipedalists

The Bipedal Adaptation

• Efficient bipedalism among primates is found

only among hominids.

• All the major structural changes required for

bipedalism are seen in early hominid fossils.

• Some researchers believe these early humans

also spent considerable time in the trees.

Disadvantages of Bipedalism

Difficult childbirth

Lower back painHernias Varicose veins

Why Hominids Became Bipedal

Many theories to explain why bipedality evolved.

Probably a combination of factors occurring over a

great deal of time.

Theories:• Carrying

• Long distance walking

• Hunting

• Gathering

• Visual surveillance

• Male provisioning

• Thermo-regulation

• Feeding from bushes

Theories:

Carrying

upright posture freed the arms

to carry various objects

including offspring.

Theories:

.

Theories:

.

Humankind Emerging, 7th ed., p. 275

Theories:

Long-distance walking

Covering long distances is

more energy effective for a

biped than for a quadped.

Theories:

.

Theories:

Hunting

carrying weapons and energy

efficient long-distance walking

made hunting more practical.

Theories:

.

Theories:

Gathering

feeding on seeds and nuts occurred

standing upright.

Theories:

Feeding from bushes

upright posture provided access to

seeds, berries, etc., in lower branches

Theories:

Visual surveillance

standing up provided better view of

surrounding countryside (view of

predators and other group members).

Theories:

Visual surveillance

Theories:

Visual surveillance

Theories:

Visual surveillance

Theories:

Visual surveillance

Theories:

Visual surveillance

Theories:

Male provisioning

males carried back resources to

dependent females and children.

Theories:

Humankind Emerging, 7th ed., p. 270

Theories:

Thermoregulation

for body cooling. Vertical posture

exposes less of the body to direct sun.

Theories:

Theories: