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
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
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
feet
The big toe is enlarged and brought in line with the
other toes
An arch forms, helping absorb shock and adding
propulsive spring.
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
Hernias
Varicose veins
Lower back pain
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
• Visual
surveillance
• Long distance walking
• Male provisioning
• Hunting
• Thermo-regulation
• Gathering
• Feeding from bushes
Theories:
Carrying
upright posture freed the arms to
carry various objects.
Theories:
Long-distance walking
Covering long distances is more
energy effective for a biped than for a
quadruped.
Theories:
Hunting
carrying weapons and energy efficient
long-distance walking made hunting
more practical.
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:
Male provisioning
males carried back resources to
dependent females and children.
Theories:
Thermoregulation
for body cooling. Vertical posture exposes
less of the body to direct sun.
Theories:
Thermoregulation
for body cooling. Vertical posture exposes
less of the body to direct sun.