GENERAL SCOPE AND USES OF PHYSICAL/BIOLOGICAL ANTHROPOLOGY. Paper No. & Title: B.A./B.Sc. Anthropology 2 nd semester. Paper II

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1 GENERAL SCOPE AND USES OF PHYSICAL/BIOLOGICAL ANTHROPOLOGY Course name: Physical Anthropology Paper No. & Title: B.A./B.Sc. Anthropology 2 nd semester Paper II Topic No. & Title: 9/15 Human Skeleton :- Changes due to assumption of erect posture Pelvic Girdle, Femur and Foot

2 Objective: Unlike in a quadrupedal animal when an animal stand erect and walk bipedally his whole body weight is to be supported by lower extremity. In doing so a number of changes are expected particularly in the pelvic girdle, femur and foot. This module therefore attempts to explain the anatomical modification on human skeleton especially in the pelvic girdle, femur and foot and its function in carrying the body weight. Content & Script of the Programme Introduction: In the history of primate evolution man evolved from non human primates. Gradual evolution from terrestrial

3 quadrupedalism (pronograde) to semi-erect posture (clinograde) and finally to a fully erect posture (orthograde) with bipedal locomotion is the way how the evolution of locomotion from simians to man has been interpreted. Man deserves its name when he could stand erect and walk bipedally. We stand with our back vertical, legs straight and our arms and hands hanging down freely on the side of the body. On the other hand our primate relatives, even if they stand, they do it with a slopping back, bent legs and arms and hands hanging down in front of the body. The assumption of such an erect posture has consequences on our skeletal system. Anatomical modifications that took place on the skeletal system due to assumption of erect posture vary in magnitude in different parts of the skeleton. Changes are observed to be more prominent on skull, vertebral column, pelvic girdle, femur and foot.

4 Changes in Pelvic Girdle due to assumption of Erect Posture:- When an individual stands erect, his whole body weight is to be transmitted on the hind legs through pelvic girdle. Therefore the pelvis plays a great role in getting an erect posture and naturally had experienced a number of changes. It is said that pelvis changed rather more than the vertebral column during the evolution of habitual erect posture and bipedal gait (Buettner Janunsch). Some of the associated changes are : i) Among the quadrupeds, the pelvis may be like a bony cylinder flattened from side to side, with its long axis parallel to spine, and the spine parallel to the ground. When an animal stands up with its spine more or less perpendicular to the ground, the girdle is now to transmit the weight of the entire body. As a result of this

5 new stress the pelvis is now flattened downward and expanded laterally; it becomes lower and broader. Its anterior or superior end spreads out, making it funnel shaped with the small orifice directed downward. ii) It was observed that human pelvis had experienced a mosaic evolution. The three bones that make up the pelvis- ischium, ilium and pubis did not develop and change at the same rate. The ilium experienced change most and ischium the least. The ischium of man is almost the same as that of living pongidae (Washburn). The ilium shortened and broadened and bent back on ischium, and resembled fan shaped in appearance. Among the primates, the extreme shortness of human ilium puts man in position of lower pelvis relative to trunk height than any other primate (Hooten).

6 iii) The excessive breadth of the sacaral part of the human ilium also helps in transmitting the whole body weight. iv) The ilio-sacral articular surface of the ilium is placed far above the acetabulum in other primates, as such there is no bony structure opposite to acetabulum. In case of man the lower part of the sacrum lies opposite to the acetabulum. v) Proportionately, human pelvis exhibits much larger and thicker acetabular region than that of other primates. This also helps in transmitting and supporting the body weight femur whose head articulate with it. vi) The acetabulum lies in the middle of the ilium and ischium, unlike those of pongids among whom the acetabulum is located well below.

7 vii) The sacrum is shorter and broader and the inlet of the pelvis forms a broad bottomless basin which supports pelvic viscera. Changes in Femur due to assumption of Erect Posture:- In an erect standing animal the entire weight of the trunk and upper extremity is to be transmitted from the pelvis to the femur which in turn supports the same. Therefore in order the bear the load of the weight, the femur has to experience a number of modifications from the femur of the quadrupedal or semi erect postured primates. The following are the modifications are observed on the femur of man due to assumption of erect posture.

8 i) In contrast to other primates, human legs (lower extremity) are longer than arms, as such the femur is long and stout. To meet the pressure of the body weight. Infect femur is the longest, largest and strongest single bone of human body. ii) The condyles (lateral and medial) are comparatively larger than those of other nonhuman primates because of the fact that joints of the leg need to have large and stout structures for supporting the body weight. iii) The ridges for muscle attachments in the femur are much more sharply defined and differentiated than other non-human primates. To be more particular, the linea aspera a prominent rough ridge which runs along the length of the diaphysis on the posterior surface

9 is distinctly present. It is the ridge where the extensor muscles responsible for erect posture and bipedal gait are attached to iv) The femur is angled outward from the knee rather than standing upright as observed among the great apes. This carrying angle ensures that the knee is brought well under the body and closer to the line of action of body weight. v) The callo-diaphysial angle i.e. neck-shaft angle is larger in man compared to apes and other primates. This obtuse angle helps to support heavier weight as compared to lower angle. vi) The poplitial surface is also more concave as compared to apes. This may also have some significance in erect posture.

10 Changes in Foot due to assumption of Erect Posture:- With the assumption of erect posture and bipedal walk, the hind limb is no longer a grasping organ but locomotory organ. As such changes necessary for modifying this grasping foot into an organ capable of supporting the weight of the body is fairly clear. i) The great toe and its supporting metatarsal bones must be brought into the line of the long axis of the foot; for a divergent toe, sticking out like a thumb would be a hindrance to ground walking, since it would be stubbed almost constantly. Therefore, all the toes are in a line.

11 ii) The big toe is no more opposable since the foot as a whole is not a grasping organ. Because of this, it also became shorter than the thumb. iii) The four lesser toes being no longer used for grasping now underwent a process of shortening and degeneration. iv) The great toe is not separated from other toes and all the meta tarsal are bound together by a common ligament. v) The weight of the body is transmitted from heel to great toe during walking. Therefore the foot has been modified with the development of transverse and longitudinal arches which help to absorb shocks.

12 vi) Elongation and strengthening of the calcaneum is another modification so that the weight is easily transmitted. The talus bone is also enlarged and wedge shaped to serve the purpose of transmitting the weight to the great toe while walking. Conclusion: So these are some of the anatomical changes or modification that we have observed on the pelvic girdle, femur and foot of man due to assumption of erect posture. Glossary Acetabulum - Hemispherical articular socket where head of femur and pelvis articulate Calcaneum - Heel bone

13 Callo-diaphysial angle - Angle formed by neck and shaft of a femur Condyle - A concave or convex prominence forming part of a joint. Femur Thigh bone Ilium Thin, blade and fan shaped bone of pelvis superior to acetabulum Ilio-sacral articular surface Articular surface of ilium and sacrum Ischium Blunt, postero-inferior part of the pelvis bone Linea Aspera - A prominent rough ridge along the length of the shaft of femur on the posterior (backside) surface Orthograde Erect posture and bipedal gait Pelvis Hip bone of pelvic girdle Phalanges Bones of fingers and toes Pronograde Quadrupedal posture Pubis Antero-inferior part of the pelvis bone

14 References: Bender L, H. David, K.Denis, L.Gordon, P.Steve, S.Jamie Stokes; The Facts On File Illustrated Guide to the Human Body: Skeletal and Muscular Systems ; Facts On File, Inc.132 West 31st Street, New York (2005) B.D. Chaurasia. Human Osteology; CBS Publishers & Distributors, 435, Jain Bhawan, Bhola Nath Nagar Delhi (1991) Boyle Mike, B. Indge K. Senior. Human Biology. Collins Educational, Harper Collins Publishers, Ltd Fulham Palace Road. London ( 1999) Hooton E.A. Up From the Ape. Motilal Banarasidass, Bunglow Road, Jaahar Nagar, Delhi (1965) Gray sanatomy of the Human Body Comparative skeletal antomy,

15 Janusch Buettner.J. Origin of Man. Wiley Eastern Pvt. Ltd. New Delhi (1969) Jones Steve,M. Robin,D. Pilbeam. Cambridge Encyclopedia of Human Evolution; Cambridge University Press. (1992) Katzenberg.M.A, S.RShelley; Biological Anthropology of the Human Skeleton. John Wiley and Sons, Inc. Hoboken, New Jersey (2008) Singh I.P, M.K. Bhasin. A Manual of Biological Anthropology. Kamala-Raj Enterprises, Delhi, India (2004) Tim. D. White, F.A. Pieter; The Human Bone Manual. Elsevier Academic Press, 30 Corporate Drive Suite 400, Burlington, USA (2005) Frequently asked questions: 1. Briefly enumerate the modification of skull due to assumption of erect posture.

16 Ans - 1. Change in the position of foramen magnum from 8 th O clock position to 6 th O clock position, 2. The jaws (maxilla and mandible) recede and reduced in size, 3. The U-shaped dental arch has now changed to a parabolic shape, 4. The area of muscle attachment on the underside of the backend of the skull (nuchal region) reduced, 5. Cranium lacks mid sagittal and lateral crests, of supra-orbital torus, 7.Reduced facial region. 6. Absence 2. Briefly enumerate the modification of vertebral column due to assumption of erect posture. Ans - 1. Formation of four alternative curves, 2. The spinous process of the vertebrae are comparatively reduced in size, 3. The size of the vertebrae progressively and successively increased in width from cervical to sacral vertebrae, 4. The sacrum became wedge shape. Summary: Quadrupadal primates walk with their legs bent, trunk parallel to the ground and head drooping down. This mode

17 of locomotion gradually evolved to an orthograde posture of man where he walk with his trunk perfectly vertical, head well balanced on the vertebral column, legs straight and arms hanging down on the side of the body. And during this course of evolution a good number of anatomical modifications took place on the skeleton of man. Both the axial as well as appendicular skeleton experienced changes to adapt to the changing environment of bipedal gait. As for axial skeleton is concerned major changes are noticed in the skull and vertebral column. Skull experienced a change in the position of foramen magnum from 8 o clock position as observed among the pronograde primates to 6 o clock position in man. With the reduction of maxilla and mandible, the size of the teeth and corresponding parts of the jaw also proportionately decreased and making the U- shaped dental arch into a parabolic shape. The mandible being small, there is no need for supra-orbital torus to

18 fasten the muscles and facilitate the skull to be well balanced. The formation of four alternative curves viz. cervical convexity, thoracic concavity, lumbar convexity, and sacral concavity makes the vertebral column S shaped structure in man unlike the bow shaped as the Pronograde primates. Cartilaginous elastic tissues in the inter-vertebrae acts as shock absorber, widening of cervical to sacral vertebrae and sacrum helps in supporting and transmitting the body weight.

Bipedalism. Bipedalism - on two feet. The single most distinctive feature of Hominids. Hominid bipedalism is habitual and required

Bipedalism. Bipedalism - on two feet. The single most distinctive feature of Hominids. Hominid bipedalism is habitual and required 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