Under the scorching heat of Tanzania, in the outskirts of the Serengeti National Preserve, a disheveled band of archaeologists crawls on top of one of the richest sites of ancient human fossils and artifacts in the world. It is the Olduvai Gorge, a location so remote that water and food have to be delivered by trucks in a three day journey. As they brush away dirt and pebbles under the indifferent gaze of the Maasai guards scouting for lions and wild animals, bioarchaeologist Ainara Sistiaga runs around the excavation collecting soil samples. She will send these samples to her lab at MIT for analysis, hoping to find invisible chemical trails preserved in the sediments after millions of years. She hopes her work will reveal information about the environment, diet and habits of our ancestors in ways unattainable by traditional archaeology.
Sistiaga is spearheading a new wave of archaeologists and paleontologists using a new array of analytical methods that go beyond collecting and measuring bones and stone artifacts. These techniques are largely based on biomarkers –natural products that can be traced to their biological origin. The new information they are unearthing is challenging long-held notions about our extinct ancestors, including Neanderthals and other human species. They are also providing accurate measurements of the climate, abundance of vegetation and presence of water in prehistoric times in places like Olduvai.
“Archeology has changed from being a very traditional field to something resembling a scene from CSI,” explains archaeologist Manuel Dominguez-Rodrigo, director of the Olduvai Paleoanthropological and Paleoecological Project, one of the two active excavation projects in the Olduvai Gorge. “New techniques are allowing us to see things invisible to the naked eye that are revealing aspects of our human ancestors’ behavior we had never imagined.”
Years ago archaeologists studying ancient humans lacked the tools to do complex biochemical analysis of their findings. They had to draw conclusions by proxy, inferring what they knew about diet, behavior, intelligence or skills from the shapes and measurement of fossilized bones and stone tools. When dating these artifacts, they relied on the geological strata in which they were found. Starting in the late 1940s carbon 14 dating became available and scientists could reliably determine the age of samples containing organic matter up to 50,000 years old.
The development of new analytic techniques like mass spectrometry and gas chromatography during the second half of the twentieth century allowed researchers to precisely identify chemicals compounds and isotopes present in a given sample. This marked the beginning of the use of organic residue analysis in archeology. Over the years biochemists have identified and characterized dozens of molecules that can serve as biomarkers and reveal information about the living organisms that produced them. However, they have not been widely used by archaeologists who usually lack the specialized equipment and cross-disciplinary laboratory skills. “They are expensive and not every archaeology department has the technical expertise and lab access to use them,” says Tommas Plummer, an anthropology professor at Queens College in New York.
In 2014 Sistiaga made waves after she made a surprising discovery. She was looking for proof of food processing in ancient fireplaces at the Neanderthal archaeological site of El Salt in southern Spain when she found a chemical compound called 5β-stigmastanol. This substance is a product of the digestion of vegetable lipids by human gut bacteria. Sistiaga, then a graduate student at a small Spanish university, appeared in the international press and television as the discoverer of “the world’s oldest poop.” Her finding was a direct proof that Neanderthals ate vegetables and challenged the long-standing view that they were exclusively meat eaters.
Now she is applying similar techniques in Olduvai, joining an ongoing effort to paint the complete picture of the prehistoric environment where at least two species of our oldest known ancestors, Homo habilis and Paranthropus boisei, once thrived and evolved. Thanks to biomarkers, researchers can know the amount of vegetal cover in any specific area and track changes in terrain features. Since they already had the fossils, they also have a clear idea kind of fauna that inhabited these lands. They can also know how long a group stayed in a certain location, even if it was only a couple of days. “Now we are able to recreate the whole topography and vegetation of a site as it was two million years ago,” says Dominguez-Rodrigo, “and have a very complete image of the environment where those humans lived.”
This knowledge is allowing Dominguez-Rodrigo and his team to start figuring out our ancestors’ behavioral patterns. They have realized that animal remains with marks of stone tool cuts have been found in higher quantities in the zones that used to have thicker vegetation, showing that ancestral humans preferred to butcher their prey in the safety of the woods. This precise knowledge of the habitat offers great opportunities to explain ancient peoples’ hunting and living habits beyond speculation based on anatomical features.
Biomarkers are also allowing researchers to understand the environmental changes that forced early humans to leave the comfort of ancestral forests and venture into open lands. Plummer has found that grasslands were becoming the predominant landscape and forests were in retreat two million years ago, at the time when the humans at Olduvai where hunting in open terrain and retreating to forested areas for safety. In 2009 he published a study based on the isotopic content of fossilized teeth enamel of herbivores found at the Kanjera archeological site in Kenya, proving that they ate mostly grass. He thinks that at that time humans were repeatedly venturing into the open pastures and that situation lasted thousands of years.
Archeologists are now asking new and bolder questions. In early 2016, a group of researchers recovered proteins from fossilized ostrich eggshells dating from four million years ago. Since proteins are a direct product of DNA expression, the scientists expect to open new avenues to resolve the family tree of the genus Homo in Africa. Sistiaga in now trying to shed light into Neanderthal microbiome, a field of study opened by her own findings. That would be a great breakthrough since access to a richer diet could have been a key driver in the evolution of early humans. Finding the bacteria able to process that diet would yield a more detailed picture of the whole process. Dominguez-Rodrigo and Plummer aim to get new insights in behavioral aspects. “These techniques are just taking off but thanks to them we are already able to know the size of the human groups that inhabited this lands and determine how long they stayed in a certain site with a precision of days,” says Dominguez-Rodrigo.
As new analytical tools become available and more archaeologists embrace them, the picture of human evolution gains depth and detail. Now we can imagine Neanderthals complementing their meaty diet with seasonal berries and fruits. In Eastern Africa we see how two million years ago certain groups left the safety of shrinking forests and ventured into the grasslands, where they hunted ungulates and other herbivores. Eventually they sought shelter in forested patches where they stayed for days or weeks while butchering their prey and, presumably, manufacturing tools and other artifacts. “Soon, we expect to be able to know the whole spectrum of ancient diet and get a better understanding of how they used the territory,” Dominguez-Rodrigo predicts.