Book Review : Gaps in Tale of Human Beginnings

In the Age of Mankind: A Smithsonian Book of Human Evolution by Roger Lewin (Smithsonian Institution Press; $37.50; 256 pages; illustrated)

It’s easy to say that human beings evolved from lower animals and very hard to say exactly how it happened. As in most areas of knowledge, the closer you look at the details, the fuzzier they get.

At every stage in the story of human evolution there are puzzles and scholarly debates. The evidence--some of it very sketchy--can be read in many different ways, and each way has its adherents. Very little is settled.

“Archeology is a detective story in which all the principal characters are absent and only a few broken fragments of their possessions remain,” says Richard Leakey, one of the foremost practitioners in the field.

Roger Lewin, a science writer and biochemist with a special interest in evolution, explores the questions, the controversies and the evidence surrounding the origins of the human race in “In the Age of Mankind,” a lavishly illustrated survey of current knowledge.

Origin of Language

He masterfully traces the coming of human beings biologically and culturally, paying as much attention to the origin of language and of cities as to the descent from the trees. Though the book is somewhat dryly written, the content of the prose makes up for what it lacks in style.

The amazing part of the story is how much of it remains a mystery; 130 years after Charles Darwin published his “Origin of Species,” it is still not clear at what point our ancestors stopped being apelike and started being humanlike. It is not even clear what the criteria are for making that judgment. What is clear, Lewin says, is that humans are different in degree but not in kind from the animals that preceded us.

Until recently, human behavior was ascribed to our hominid ancestors at a fairly early stage in their development. The tide of expert opinion on this subject has now shifted.

Primitive Versions

“Our ancestors now appear to be more like apes than like primitive versions of ourselves,” Lewin writes.

Stone tools began to be used about 2.5 million years ago, but it was not until Homo erectus came along nearly a million years later that something different happened. He “was the first to use his environment as a modern hunter-gatherer does, and the first whose anatomy speaks of a humanlike social structure,” Lewin says. “For the first time, the Age of Mankind seemed at hand. Before then, however, the menagerie of hominid species inhabiting various parts of Africa lived the lives of intelligent, large-bodied, terrestrial primates, some of whom made and used stone tools.”

Crossed the Bridge

Still, modern humans did not arise until somewhere between 200,000 and 150,000 years ago, and they did not leave Africa until between 100,000 and 35,000 years ago. When they crossed the then-existent land bridge between Asia and North America remains unknown.

When did they begin to speak? When did they develop consciousness? When did the hunter-gatherers settle down and turn to agriculture? No one knows.

Nor is it clear, as long thought, that language was developed for the purpose of hunting. It now appears that the spur to communication was the need for social organization. This helps to explain why humans have to be so much cleverer than animals, who, after all, manage to make a living in their environments with much less brain power.

“While primates’ subsistence environment may be no more complex than that of other mammals, their social environment is much more demanding,” Lewin writes. “More and more, language is coming to be seen as a tool of consciousness: a way of thinking better, a way of more effectively reconstructing a picture of our social world in our heads.”

Organized Cities

Finally, social organization led to cities, which began in Mesopotamia only 6,000 years ago. Civilization and modern society began in the city of Uruk between the Tigris and Euphrates rivers.

“At Uruk, to a degree unimagined in earlier phases of human history, there emerged the need for control of uncertainty; control not only over the physical elements of nature but over fellow human beings,” Lewin says. “Once you had Uruk, New York was probably inevitable: The true city, once formed, generates a whole new array of social and technological selection pressures that set a new trajectory in human history.”

But how all this happened is a matter of great controversy. There is no clear-cut distinction between causes and effects. Different stories can be put together from the same sketchy facts.

Lewin’s book is an up-to-the-minute presentation of those stories that underscores what is known, what is unknown and what is guessed at. We still have a long way to go before we can answer humanity’s age-old question: Where did we come from and how did we get here?