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13_Human_Evolution (3)

13_Human_Evolution (3) - BI SC 002 LECTURE 13HUMAN...

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BI SC 002 LECTURE 13—HUMAN EVOLUTION Draft: December 3, 2010 Our final topic for this semester is also one of our most controversial—the topic of human evolution. To classify a human, first we are an animal, because we consume food for energy. Of the animals, we are chordates because we have a spinal cord. Of the chordates, humans are mammals, which mean we have body hair, give live births, and nurse our young. Of the mammals, humans classify as primates because we have ape-like features. Before we go any further, we must say one thing: just because humans have ape-like features does NOT mean that humans descended from apes. It does NOT mean humans descended from monkeys. What this means is that humans, apes, and monkeys all have the same common ancestor and each descended from this primate. It is more like humans, apes, and monkeys are cousins of each other instead of one being the parent/grandparent of the other. All primates shared a common ancestor millions of years ago. It is thought that this primate may have resembled a tree shrew in its size and structure. About 45 million years ago, there was an evolutionary split. The lemurs and other very small primates split from what was now the lineage for monkeys, apes, and humans. About 15 million years ago, the precursors of monkeys split from our lineage. About 7 million years ago was the other major split—apes separated from our lineage, and our line evolved into the hominids . Hominid is the group of classification that includes humans and human-like ancestors. Characteristics of hominids include bipedalism (the ability to walk upright, probably developed while our ancestors still lived in the trees), a shorter jaw, less specialized teeth than apes, and a larger brain size than other primates. The oldest hominid fossil, Sahelanthropus tchadensis , dates to about 7 million years ago and was discovered in eastern Africa. In fact, most of the fossils of the earliest hominids were found in East Africa.
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