Getting Down to the Bone

For the archaeologist, the excavation of a bone represents the happy completion of a long and assiduous process. It is also when the equally persnickety process of bone analysis begins. Those analyses have the power to transform a dusty artifact into a gripping story.

From a single bone tool, archaeologists can learn volumes about the intellect, behavior, and culture of a people. But what stories can a bone tool tell? And exactly how do archaeologists read them?

They must be translated through the scientific process, says Curtis Marean, ASU professor of anthropology and member of the Institute of Human Origins. Every bone requires meticulous study using several different techniques. Then, through a series of checks and balances, researchers confirm their accuracy before drawing any conclusions.

The bone tools unearthed in South Africa’s Blombos Cave were studied using this approach. By examining each artifact from multiple perspectives, the researchers were able to piece together the past.

“We reconstruct the whole process of the technology,” says Marean. “That way we can observe the choices people are making and try to understand why they’re making those choices.”

The scientific objective is to recreate the entire construction process. Marean says that it is clear that the Blombos Cave tools’ construction began with selection of the right bones.

“Some bone is better than other bone for making tools,” says Marean. “They’re making conscious choices to go out and select certain materials.”

Marean determined what bones were used to build the tools by comparing them to the bones of modern antelope.

He found that most of the bones came from lower legs and feet of deer-like animals. These animals were primarily hunted for meat. After fracturing the bones to get their marrow, people used the remaining fragments to fashion tools. They focused on parts of the bone that were naturally strong and would make an effective tool.

How did early humans transform broken animal bones into fine tools? To uncover this process, the researchers examined the angle, depth, and shape of each marking on the bones.

“Every tool was looked at under a scanning electron microscope,” a high-powered microscope that can magnify up to 2 million times. “That allows us to see the finest traces of wear,” says Marean.

Francisco d’Errico, of the Institut de Prehistoire de Geologie du Quaternaire in France, helped interpret the markings on the tools from Blombos Cave.

D’Errico’s specialty is making bone tools, using them for a variety of tasks, and studying how the processes influence the tools’ appearance. He has created his own library of tools and microscopic images of their wear patterns.

D’Errico compares his library with historical bone tools collected in the field. If the microscopic markings are similar, an excavated tool was probably produced and used similarly to d’Errico’s experimentally produced tool.

In a second sequence of tests, Chris Henshilwood, a professor at the State University of New York at Stony Brook, confirmed how the tools were used. Like d’Errico, Henshilwood did this by comparing the ancient tools to his own library. His library contains a set of more modern bone tools. Based on previous research, he knew their function. By comparing the basic forms, he inferred the function of the Blombos Cave tools.

The results of tests by Henshilwood and D’Errico showed that the tools from Blombos Cave were chipped, scraped, and polished into their final forms.

“The people would chip the bone down and create what we call a pre-form. Then they would take a stone tool and scrape it into shape further. With some of the bone tools, that would be the end. Then they went and used it,” says Marean.

“With other bone tools, they then ground that scraped surface,” he explains. “To polish bone, you would take a piece of leather and put a very light abrasive on it,” such as ochre. “It would take you hours to get that thing polished.”

The finely polished tools were projectile points used in hunting. The more roughly hewn tools were awls used to pierce clothing.

These exhaustive studies seem to have solved the mystery of how the tools were created. Equally vital to understanding human origins is the question of who produced them. Marean suspects that they were people who looked much like the native people living in South Africa today.

“The indigenous people of South Africa are Khoi-San people,” explains Marean. “We know from genetics that they are one of the most ancient lineages on the planet. Are they the original modern humans? That’s very possible,” he says.

“They, or people who looked like them and were their ancestors, may have been the people who were making those bone tools. My personal feeling is that, if we could put a face on the earliest modern humans, they would look like a Khoi-San person.”—Danika Painter