Man differs principally from all other animals by his attainment of the biped mode of locomotion. Instead of walking in a bending position supported by the arms like other animals, man walks erect.

 The changes that have undergone in the skeleton of man due to the fully erect posture are numerous and its implications of such changes are significant in understanding the evolution of man. 

The important changes in the various parts of the skeleton are noted below.

Vertebral Column

The triple curvature of the spine made the vertebral column a kind of spring-like structure that cushioned, for the head, the shock the entire body experiences with walking. 

Pectoral girdle 

Though less change is apparent in the anterior girdle, it also broadened and flattened into the scapulae.  

Forearm 

The forearm lengthened in proportion to the total length of the body, and the thumb and fingers became specialised as grasping organs.

Pelvis

The pelvis broadened and flattened, to become a kind of basin for the support not only of the internal organs, but also of the upper girdle, arms and head, that pressed down upon it. The pelvis is comparatively much shorter and broader and extends around to the side. This configuration helps to stabilise the line of weight transmission in a bipedal posture from the lower back to the hip joint. 

The Femur 

When man stood up on his feet, the femur (thigh-bone) became straighter and longer, 

The ridge or crest (Linea aspera) at the back of the human femur also became emphasised to allow for the stronger musculature that was necessary for walking and bending. 

The articulations between the bones of the leg and foot underwent alterations at knee and ankle and thus allowed more effective adjustment to erect posture.

Lower limb 

Remodelling of the lower limb to allow full extension of the knee and to keep the legs close together during walking, this maintained the centre of support directly under the body. 

The foot

The foot of man -has witnessed remarkable changes due to the assumption of erect posture. The foot is used like a prop, landing on the heel and pushing off on the toes, particularly the big toe. 

The function of the foot was completely changed from grasping to supporting which resulted in the following anatomical changes.

(a) Loss of opposability of the great toes.

(b) Development of the shock-absorbing arch.

(c) Tendency towards monodactyly.

(d) The axis of the foot running through in between the first and the second toe.

(e) Formation of the medial and lateral arches.

(f) In the fifth digit, reduction in the number of phalanges is in progress.

(g) The calcaneum becomes larger.

(h) Wedge-shaped development of the other tarsal bones.

Skull 

The human skull is well-balanced on the first vertebra, known as the atlas. At the base of the skull is the foramen magnum, a large opening that allows the spinal cord to connect to the vertebral column. This central positioning contributes to the balanced alignment of the head, resulting in a vertical orientation of the face.

Head and Face 

The changes in the head and face were profound. The jaw became much lighter, and the teeth, especially the canines, became smaller. The jawbone, or mandible, is attached to the skull by the muscles that move it, and its lighter character meant that it could be manipulated by lighter muscles. Lighter muscles meant that there was more room inside the jaw for the tongue, 

while the bones of the skull could become less rugged, when they were no longer called upon to provide the surfaces that heavy muscles require as points of attachment.  Finally, brains of a size distinctive of man alone could develop.

These changes gradually assumed the characteristics of present-day man.

There is no unanimity among scholars on why these changes occur. One scholar will argue that these came about from need, another from chance, another from the physical forces involved and another from selection. 

Implications 

Bipedal locomotion because of the inherent advantages was fundamental in bringing about the changes that made man the erect, speaking, tool-using, culture-building creature 

• Bipedal locomotion freed the hands for carrying objects and for making and using tools.
• In a bipedal locomotion, having a wider view of the surroundings and in open (or semi-open) terrain, early spotting of predators (particularly large cats, such as lions, leopards, and saber-tooths) would be of critical importance.
• Moreover, bipedal walking is an efficient means of covering long distances,