Masters of the Planet, The Search for Our Human Origins

By Ian Tattersall

Pargrave Macmillan, 2012, 288 pages, $26.00

The title of his book suggests a certain degree of anthropocentric hubris, but Ian Tattersall’s take on the paleohistory of the genus Homo is commendably restrained. Too many books on human origins present in­genious speculation as firmly established fact, linking the exceptional success of our lineage to cranial capacity, or to the ability to walk upright, or even to the peculiar ability to throw rocks. Such speculation makes for a smooth narrative, per­haps, but leaves the reader feeling a bit uneasy.

Tattersall, a curator emeritus at the American Museum of Natural History in New York City, is no slouch in the storytelling department, but his narrative empha­sizes the necessarily fragmentary nature of the fossil record and the provisional nature of what we can safely conclude from it. The earliest hominids, discovered in just the last dozen years, date from 7 million to 4 million years ago, and all we have of their remains are some crushed skulls and partial mandibles, with only a few relatively complete but crumbling skeletons. Add to the crushed bones some scattered flakes of chipped stone, along with later (perhaps no more than a half-million-year-old) stone handaxes and cleavers, and that’s pretty much all scientists have to go on for the span of thousands of millennia. Ancient hominids didn’t even leave behind symbolic artifacts prior to the ap­pearance of carvings 70,000 years ago and, beginning around 30,000 years ago, the Cro-Magnon art in European caves.

Yet scientists have been able to extract a surprising amount of information from those tantalizing finds. The shape and articulation of bones in a skeleton can be a clue to biped­ality, even if the skeleton is grossly incomplete. Quadrupeds such as chimps have spines that articulate with the back of the skull, for instance, whereas bipedal humans have skulls that perch on top of an erect spine. Even toe bones connect together differently in bipeds than they do in quadrupeds.

Only have a tooth, or a fragment of bone? Good enough for an analysis of paleodiets, since animals are what they eat. Animals that have higher abundances of carbon-13 in their bones and teeth have ingested savanna grasses, while those whose diet consists of forest fruits and vegetation have a higher ratio of carbon-12. Grazers such as antelopes fall into the former category, but so do many australopithecines, homi­nids that lived in East Africa as early as 4 million years ago. Since it’s hard to imagine any primate subsisting on grasses, the high carbon-13 levels in those early hominids suggest that they ate a fair amount of meat from animals that grazed on grasses, and that they had already developed considerable ingenuity in chasing, trapping, or scavenging food for dinner. A few atoms, in other words, imply the emergence of nov­el social and cognitive skills.

Tattersall’s account highlights the major advances in paleoanthropology that have been made in the last decade or two. A variety of new fossil finds have given us a picture of an evolutionary tree with many branch­es. DNA sampling of modern world populations has enabled us to con­firm the origin of Homo sapiens from a tiny population in Africa and to trace our species’ growth and spread south to the tip of that continent, as well as northward out of Africa and eastward and westward throughout the world. Our understanding of how we made the journey from the tropical forest to technological soci­ety is only in its infancy, but then, as a species, so are we.