The uniqueness of man

Abstract

If an animal is to evolve from a quadruped to a biped its centre of gravity must be moved backwards to rest above the hindlimbs. Animals of this type tend to have large tails like kangaroos and most species of birds. The centre of gravity of a kangaroo lies behind its hindlimbs and its weight is supported partly by the tail. In birds the trunk is set at an angle on the lower limbs so that the head is well in front and the tail projects backwards and balances the forward part of the trunk. The penguin’s posture appears exceptional, but Joseph (1960) has observed it in detail. Although the trunk of the penguin appears to be vertical a considerable part of its lower end projects below and behind the articulation of the femur with the pelvis. In addition the penguin’s lower limbs are flexed at the hips and knees (Figure 5.1).