Реферат: The Earliest Hominines Essay Research Paper The

some Miocene sivapithecine ancestor. Evolution of the hominines was not steady;

it was far more likely periods of stasis punctuated by short episodes of rapid

changes, as evidenced by long periods of little change between the diversification

of the various Australopithecus species.

At the close of the Miocene, the climates changed, with the Mediterranean Sea

drying up temporarily and the vast forests undergoing a reduction in size. More

open country was available, requiring the ancestors of the hominines, as well as the

early hominines themselves, to spend more time on the ground. New foods were

made available as older arboreal ones disappeared; dentition therefore was altered.

With the reduction of canines came, it is believed, a reliance on hands for defense,

using clubs or rocks. This use of objects for defense may have set the stage for

tool-use/tool-manufacture. There is no evidence of tool use or manufacture among

australopithecines, but modern chimps and orangs can and do make tools; in fact,

under experimental conditions, chimps have been able to make crude chipped stone

tools. Based on the abilities of modern chimps and orangs, it is believed that the

australopithecines used natural objects as tools.

There is a 2 million-year gap between the last sivapithecine and the first

australopithecine; the individuals in this gap likely were undergoing the transition

to bipedalism.

Bipedalism has drawbacks: exposure of soft belly to attack; slower running and

poorer ability to change direction instantly; back problems, hernias, circulatory

problems associated with the upright posture; and the consequences of serious leg

injury.

So why bipedalism? Perhaps for: carrying foraged foods from place to place

carrying infants so that fatal falls from mother were minimized; faster food

gathering and longer treks with less fatigue; spotting food sources or predators

from a distance with the increased height and visual perspective of standing on the

hind limbs; or freeing hands to fend off predators by using natural objects as

weapons. In any case, the bipedal adaptation was likely the result of several