Evolution

10 Pages 2492 Words

in brain size may be related to changes in hominine
behavior. Over time, stone tools and other artifacts became increasingly
numerous and sophisticated. Archaeological sites, too, show more intense
occupation in later phases of human biological history. In addition, the
geographic areas occupied by our ancestors expanded during the course of human
evolution. Earliest known from eastern and southern Africa, they began to move
into the tropical and subtropical areas of Eurasia sometime after a million
years ago, and into the temperate parts of these continents about 500,000 years
ago. Much later (perhaps 50,000 years ago) hominines were able to cross the
water barrier into Australia. Only after the appearance of modern humans did
people move into the New World, some 30,000 years ago. It is likely that the
increase in human brain size took place as part of a complex interrelationship
that included the elaboration of tool use and toolmaking, as well as other
learned skills, which permitted our ancestors to be increasingly able to live in
a variety of environments. The earliest hominine fossils show evidence of marked
differences in body size, which may reflect a pattern of sexual dimorphism in
our early ancestors. The bones suggest that females may have been 0.9 to 1.2 m
(3 to 4 ft) in height and about 27 to 32 kg (about 60 to 70 lb) in weight, while
males may have been somewhat more than 1.5 m (about 5 ft) tall, weighing about
68 kg (about 150 lb). The reasons for this body size difference are disputed,
but may be related to specialized patterns of behavior in early hominine social
groups. This extreme dimorphism appears to disappear gradually sometime after a
million years ago.

Face and Teeth The third major trend in hominine development is the gradual
decrease in the size of the face and teeth. All the great apes are equipped with
large, tusklike canine teeth that project well beyond the level of the other
te...