Ian Tattersall's 'Masters of the Planet' looks to pinpoint what made us human

By Alan Nalbach

masters.jpgMacMillan, 266 pp., $26
For millennia, philosophers have struggled to define what makes us human. Today, paleoanthropologists -- archaeologists, biologists and social scientists studying ancient hominids and early humans -- grapple with an even thornier question: What made us human?

Ian Tattersall, curator of the Division of Anthropology of the American Museum of Natural History in New York, illuminates the challenges of this endeavor in "Masters of the Planet," an efficient survey of 7 million years of evolutionary development and two centuries of evolutionary thought.

The core of the work is "a chronological account of the long and astonishing process whereby our ancient ancestor, an unusual but not particularly extraordinary primate variation, became transformed into the amazing and unprecedented creature that Homo sapiens is today."

In deft combinations of authority and caution, expertise and wit, Tattersall invites the lay reader to the party. Throughout, he remains grounded in the salient details culled from archaeology, anatomy, genetics, primatology, nutrition and social science.

He offers close descriptions of stones and bones -- craniums and teeth, pelvises and ankles, thumbs and wrists, even shoulder blades -- and their significances for mobility, dexterity and other attributes. I often found myself clicking my teeth or rolling my hips as I read.

Still, the story of hominid evolution remains cloudy and contentious, and the lack of resolution requires Tattersall to take detours into paleoanthropological discoveries and debates. There is the challenge of determining the defining criteria by which hominid species should be distinguished from one another. There is also the question of whether morphology (shape) or chronology (age) should determine how individual specimens should be assigned to particular species.

The "persistence of the old along with the new," both between and among hominid species, renders both undertakings especially tricky.

That persistence illuminates one of Tattersall's more thought-provoking insights: namely, that most major breakthroughs in human behavioral development -- upright walking, the creation of particular types of tools or the development of symbolic cultures -- likely occurred not at the origin points of particular species, but well within their development.

As Tattersall notes, you can't use a structure -- a hip socket, an opposable thumb, a larger brain -- until you have it. Rather than physical "adaptations" to environmental changes, potentially advantageous physical traits might be better thought of as "exaptions"--"features that are acquired through random changes in our genetic codes, to be co-opted only later for specific uses."

In this way, he argues that our capacity for symbolic thought evolved without environmental pressure.

Tattersall also provocatively reminds us of the difficulty, if not the impossibility, of imagining the consciousness and cognitive systems of other species. Earlier hominids and human species were not, he insists, like us but merely dumber. The archaeological evidence of their ways of life suggests they likely knew a great deal of information, but (if analogies to modern-day primates are valid) they were unable to reflect on what they knew, why they knew it or what others knew.

Archaeologists have found no evidence of the symbolic mental manipulation of information among the remains of australopithecines, Homo erectus, the Neanderthals or any other hominid or human species but our own. This, Tattersall believes, is what distinguished "us" from "them": "We are symbolic."

The earliest traces of decorative arts have been found in South Africa, dating to around 76,000 years ago. But Tattersall posits that it was the development of language, "the ultimate symbolic activity," which proved decisive in modern humanity's mastery of the planet.

Tracking the diffusion of genotypes has revealed that modern humanity originated in Africa; the global diffusion of phonemes (the sounds used to make speech) suggests that language may also have originated there. But the precise development responsible for this breakthrough -- intensifying sociability, a certain part of the brain, or a cognitive system --remains unclear.

Fellow paleoanthropologists have audaciously staked their reputations on this and other questions, but Tattersall maintains a prudent if tantalizing circumspection in "Masters of the Planet."

Alan Nalbach is a critic in Bay Village, Ohio.