Humans: An Evolutionary History ORIGINS - Rebecca Stefoff Part 4 ppsx

grasp things—on all four feet; flat nails rather than claws on at least some

of their digits; a brain that is large for their overall body size; and eyes that

are large and set facing forward in the front of the face. The Eocene world

was warmer than the modern world, with tropical temperatures and forests

extending far north and south of the equator. The forest-dwelling primates

spread throughout the world, with the likely exception of Australia and

Antarctica, where no primate fossils have been found.

Scientists think that all of these early primates were arboreal. They

moved around by jumping and by running along branches. Their main food

was insects, although later some of them began eating plant foods. Most

early primates were probably nocturnal, or active at night. Their eyes were

bigger and their noses were smaller than those of the ancestral mammals,

showing that the primates relied more on sight and less on scent.

About 40 million years ago temperatures on Earth began to cool. The

lush forests disappeared from places like North America and Europe, and

so did the primates. Only in Africa, which remained covered with thick trop￾ical forests, did primates continue to flourish. New types of fruit-eating pri￾mates evolved. Fossil deposits from Fayum, Egypt, show that North Africa

had a large and diverse group of these species between 36 and 31 million

years ago. Scientists think that the primates of this era were the ancestors

of both monkeys and apes. By about 35 million years ago some primates—

the ancestors of the New World monkeys—had reached the Americas.

(The details of this migration are unknown, but primates could have been

carried on floating logs or mats of vegetation across the Atlantic Ocean,

which was narrower than it is now.) And by 20 million years ago a new kind

of primate had evolved in Africa: the ape.

Ancient Apes

Several features set apes apart from other primates. Apes lack tails. Apes’

elbow joints allow them to rotate their forearms far more than monkeys

can (humans can do the same thing). Apes are generally larger than mon￾ORIGINS

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