Word: upright
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...that kadabba walked upright at all is hugely significant. Paleontologists have suspected for nearly 200 years that bipedalism was probably the key evolutionary transition that split the human line off from the apes, and fossil discoveries as far back as Java Man in the 1890s supported that notion. The astonishingly complete skeleton of Lucy, with its clearly apelike skull but upright posture, cemented the idea a quarter-century...
...wisdom has long focused on the fact that eastern Africa became significantly dryer about the time that humans first evolved. The change would have tended to favor grasslands over forests, and, so went the theory, our ancestors changed to take advantage of the new conditions. We learned to walk upright so that we could see over the tall grasses to spot predators coming; an upright posture, moreover, would offer a much smaller target for the oppressive heat of the grassland sun, and a larger target for cooling breezes...
...advantages of walking upright were somehow so great that the behavior endured through thousands of generations. Indeed, the anatomy of our ancestors underwent all sorts of basic changes to accommodate this new way of moving. Many of the changes help the body stay balanced by stabilizing the weight-bearing leg and keeping the upper torso centered over the feet. Lovejoy, who studies the anatomy and biomechanics of locomotion, thinks the changes may have improved coordination as well. "To walk upright in a habitual way, you have to do so in synchrony," he says. "If the ligaments and muscles...
...allowing the lower spine to curve, which locates the upper body over the pelvis for balance. The pelvis grew broader, meanwhile, and humans developed a hip joint and associated muscles that stabilize the pelvis. Explains Lovejoy: "That's why a chimp sways from side to side as it walks upright and humans...
Changes also had to take place in the femur, or thighbone. For example, the femoral neck--the bent portion at the top of the bone--is broader in humans than it is in apes, which improves balance. The human knee is specialized for walking upright too: to compensate for the thighbone's being at an angle, there's a lump, or groove, at the end of the femur that prevents the patella from sliding off the joint. "A chimp doesn't have this groove because there is no angulation between the hip and the knee," Lovejoy says. "This change says...