The Origin of Humankind Read Online Free PDF Page B

know whether they were those of a bipedal ape or a conventional ape? It’s an exciting challenge.
    If we could visit the Africa of 7 million years ago to observe the behavior of the first humans, we would see a pattern more familiar to primatologists, who study the behavior of monkeys and apes, than to anthropologists, who study the behavior of humans. Rather than living as aggregations of families in nomadic bands, as modern hunter-gatherers do, the first humans probably lived like savanna baboons. Troops of thirty or so individuals would forage in a coordinated way over a large territory, returning to favored sleeping places at night, such as cliffs or clumps of trees. Mature females and their offspring would make up most of the troop’s numbers, with just a few mature males present. The males would be continually looking for mating opportunities, with the dominant individuals achieving the most success. Immature and low-ranking males would be very much on the periphery of the troop, often foraging by themselves. The individuals in the troop would have the human aspect of walking bipedally but would be behaving like savanna primates. Ahead of them lay 7 million years of evolution—a pattern of evolution that was complex, as we shall see, and by no means certain. For natural selection operates according to immediate circumstances and not toward a long-term goal. Homo sapiens did eventually evolve as a descendant of the first humans, but there was nothing inevitable about it.

CHAPTER 2
A CROWDED FAMILY
    B y my count, fossil specimens of varying degrees of incompleteness, representing at least a thousand individuals of various human species, have been recovered from South and East Africa from the earliest part of the record—that is, from about 4 million years ago up until almost a million years ago (many more have been found in the later record). The oldest human fossils found in Eurasia may be close to 2 million years old. (The New World and Australia were populated much more recently, some 20,000 and 55,000 years ago, respectively.) It is fair to say, therefore, that most of the action of human prehistory took place in Africa. The questions anthropologists must answer about this action are twofold: First, what species populated the human family tree between 7 million years ago and 2 million years ago, and how did they live? Second, how were the species related to each other evolutionarily? In other words, what was the shape of the family tree?
    My anthropological colleagues face two practical challenges in addressing these problems. The first is what Darwin called “the extreme imperfection of the geological record.” In his Origin of Species , Darwin devoted an entire chapter to the frustrating gaps in the record, which result from the capricious forces of fossilization and later exposure of bones. The conditions that favor the rapid burial and possible fossilization of bones are rare. And ancient sediments may become uncovered through erosion—when a stream cuts through them, for instance—but which pages of prehistory are reopened in this way is purely a matter of chance, and many of the pages remain hidden from view. For instance, in East Africa, the most promising repository for early human fossils, there are very few fossil-bearing sediments from the period between 4 million and 8 million years ago. This is a crucial period in human prehistory, because it includes the origin of the human family. Even for the time period after 4 million years we have far fewer fossils than we would like.
    The second challenge stems from the fact that the majority of fossil specimens discovered are small fragments—a piece of cranium, a cheekbone, part of an arm bone, and many teeth. The identification of species from meager evidence of this nature is no easy task and is sometimes impossible. The resulting uncertainty allows for many differences of scientific opinion, both in identifying species and in discerning the