Our Adaptable Ancestors

In novels and movies, archaeologists leap over pits, swing from vines and disarm ingenious traps as they gallivant around the world in search of buried treasure. They behave less like scientists than swashbuckling explorers with an old map and a loose grasp of history. But in the summer of 2003, a group of real archaeologists excavating a site in Olorgesailie, Kenya, discovered treasure as exciting as any in fiction. They were pursuing a greater understanding of humanity's ancestors, and their real-life adventure offers us revelations in the epic and evolving story of mankind.

The scientists, affiliated with the Smithsonian Institution and the National Museums of Kenya, uncovered 11 skull fragments belonging to a single, diminutive early hominid about 900,000 years old. The fragments, including a partial cranium, a portion of a brow ridge and pieces of the braincase, help to fill in a 400,000-year gap in the human fossil record in Africa. Studying the fragments and early tools found nearby and, especially, how the landscape and environment of the area changed over time can help the scientists at Olorgesailie and elsewhere determine how early hominids evolved to become today's Homo sapiens.

That new focus has led them to ask why the early hominid is so much smaller than those of a similar age found at sites in Europe and Asia. One hypothesis suggests scarce natural resources are the cause. Because scientists now believe that humans evolved from closely related but noticeably different groups of individuals, the smaller pre-humans may have existed for only a short while or may have eventually been drawn back into the main gene pool. Discoveries of such fossils also provide clues about the behavior of early humans, giving us an appreciation of how our ancestors interacted with plants and animals. For instance, bite marks along the individual's brow ridge imply he met an untimely end from a carnivore. Other discoveries reveal how skilled the early humans were. By studying the stones they used for making hand axes, scientists may match them with existing rock faces, thus deriving how far the early humans traveled. Those at Olorgesailie used mostly rocks they found within a three-mile radius, but some of their tools were made from rocks they found up to 30 miles away.

The Smithsonian's Human Origins Program—an international effort that encompasses four active archaeological sites stretching from East Africa to East Asia—has pioneered the study of how these hand-ax makers adjusted to rapidly changing natural surroundings, giving us a good glimpse of our ancestor, the toolmaker. The scientists' conclusions are made possible by several new excavation techniques they've developed. In the early 20th century, archaeologists typically dug pits, which provided narrow windows into the planet's history. Today, the scientists at Olorgesailie not only dig deeply but also follow a single layer of the fossil record for many miles across the landscape. They want to understand the roots of human adaptability, a new question for science but one of vital importance. Their research has already detailed the environmental conditions early humans faced, how those conditions changed and how early humans adapted.

The resourcefulness of early humans is one reason scientists find so few human fossils from that period. Early humans moved away from their first homes, near watering holes and lowlands. Fossils there are well preserved, but predators such as lions and hyenas posed a constant threat to the hominids. So they moved to higher ground, where fossils are not well preserved, and only went to the lowlands to obtain food and water. As the Olorgesailie scientists begin another season of digging and discovery, they will be looking for further traces of early toolmakers in regions where the lowlands meet the rocky Rift Valley, and they will continue to build on their long-term collection of data about the roots of human interaction with the natural world. Understanding that will help them tell us the complete story of our early ancestors and how they survived.

Lawrence M. Small | READ MORE

Lawrence M. Small was the eleventh secretary of the Smithsonian Institution, serving from 2000 to 2007.