E. Blaker
Human ancestors were using stone tools and butchering animals for meat 800,000 years earlier than previously thought, according to a paper published in the science journal, Nature, last month. A multinational team of scientists discovered the fossil remains of butchered animals in Dikika Ethiopia, not far from the site where evidence for stone tool making was found, but the stone tools are hundreds of thousands of years younger than the newly discovered fossils.
“This discovery dramatically shifts the known timeframe of a game-changing behaviour for our ancestors,” says Zeresenay Alemseged, a paleontologist of the California Academy of Sciences. “Tool use fundamentally altered the way our earliest ancestors interacted with nature, allowing them to eat new types of food and exploit new territories. It also led to tool making – the precursor to such advanced technologies as aeroplanes, MRI machines, and iPhones.”
In early 2009, a group of scientists led by Dr. Alemseged found a smaller than six inch long piece of fossilized rib bone from a cow-like animal and a short length of thigh bone from another grazing animal the size of a goat. The fossils had weathered out of a sandy layer of rock in the harsh, treeless canyon-lands of the Ethiopian desert. What makes these small pieces of bone special is that they bear the cuts and scrape marks of purposeful butchering.
“Most of the marks have features that indicate without doubt that they were inflicted by stone tools,” explains Dr. Curtis Marean from the Institute of Human Origins at Arizona State University, who performed the mark identifications.
But how can scientists be sure the cut marks on the bones were made during ancient times, and not recently? To find out, the marks were examined using a special kind of scanning electron microscopy. The technique allows analysts to not only clearly see tiny details of the cut marks, but also to determine the chemical composition of the surface of the fossil. By comparing the chemical makeup of the interior of the cut marks with that of the uncut surfaces, the researchers were able to ascertain that the cut marks were of ancient origin.
To determine the age of the fossils, the researchers needed to know the age of the rock layers encasing them. So they measured the proportions of two forms of argon gas trapped within tiny crystals when the rock was formed. Geologists calculate the age of the rock using the known rate of change of the gas from one form to the other.
“We can very securely say that the cut-marked bones date to between 3.42 and 3.24 million years ago, and that within this range, the date of the bones is most likely 3.4 million years ago,” says project geologist Dr. Jonathan Wynn from the University of South Florida.
This begs the question of who, back in the hazy dawn of human ancestry, used the stone tools to butcher these particular animals. Who was in the neighborhood back then? “The only hominin species we have in this part of Africa at this time period is A[ustralopithecus] afarensis, and so we think this species inflicted these cut marks on the bones we discovered,” notes Alemseged. The most famous human ancestor, ‘Lucy,’ was a member of this species.
But so far, no stone tools or the evidence of their manufacture have been found that are as old as the recently discovered animal bones bearing the cut marks. There are no rocks within 6 kilometers of the area that are big enough to be used as tools, or for tool making. Were Lucy’s kin able to plan ahead well enough to bring the tools with them?
“This new discovery will cause us to refine our ideas about dietary and cognitive evolution in our early ancestors,” said Leslie C. Aiello, an anthropologist and the president of the Wenner-Gren Foundation in New York, who was not involved with the project. “It would be nice to have some stone tools from this period and more than two bones as evidence; however, this is enough to demonstrate that there is still a lot to learn about these early phases of hominin evolution.”
Shannon McPherron, a paleontologist from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany summed up the next challenge: “ One of our goals is to go back and see if we can find these locations and evidence that at this early date they were actually making, not just using, stone tools.”
Elizabeth Blaker - writer 