A team of international researchers led by the University of Victoria's April Nowell has discovered 250,000-year-old protein residue – the oldest ever found – extracted from stone tools used by early humans.
The finding, from Azraq, Jordan, has led to direct evidence that humans from this period were pursuing specific animals in an attempt to survive.
Dr. Nowell says researchers have long suspected this type of behaviour, but evidence this ancient is unprecedented.
Information accessible through the testing of protein residue from this period could change the way researchers study the diets of early humans, especially in cases where no animal bones can be recovered.
A report into the findings, co-authored by a group of collaborating Canadian, American and Jordanian researchers, will be published in next month's edition of the Journal of Archaeological Science.
Dr. Nowell, a professor of anthropology, says that while researchers had found bones at the site belonging to some of the species they were able to identify in the protein residue tests, some species came as a surprise.
"It really makes visible something that was previously invisible to us," she said.
Dr. Nowell says that by knowing what kinds of species were hunted and scavenged during this time – in this case, horse, rhinoceros, duck, wild cattle and camel – researchers can tackle more nuanced questions about the strategies that were used to do so.
She says the findings show that hundreds of thousands of years ago, early humans were adapting to tough conditions by going after a range of prey.
Dr. Nowell's team has been working on the research in Azraq since 2013, during which they uncovered 10,000 stone tools, examining 7,000 of them.
Of these, 44 were sent for protein-residue tests at a lab in Portland, Ore., and 17 came back with positive results.
Francesco Berna, an assistant professor at Simon Fraser University's Department of Archeology, explained in an e-mail that the team's findings will "allow us to learn about the behaviour and diet of human ancestors" and provide "new scenarios for the study of stone tools and ancient societies."
But Dr. Berna noted that the while the Azraq basin is a "very arid" area that could permit the preservation of organic material for a long time, 250,000 years "seems unlikely."
Cameron Walker, a professor at Oregon Health and Science University and a co-author of the report, said few archeologists have considered using protein-residue testing to find the information they seek.
"What's helpful about doing that is that most animals have a differing immunoglobulin G [a protein antibody] from each other … for example, you and I don't have the same proteins as a rhinoceros would, nor do we have the same proteins as a duck or a squirrel or any other mammal," he said.
Dr. Walker says protein-residue analysis is often dismissed due to an assumption that the preservation required to keep samples intact isn't possible.
Hopefully, he says, that notion is changing.
"There have been soft tissues preserved from the era of dinosaurs 60 million years ago and change, so in an appropriate burial environment where we get lucky and everything is dry and the stone tool was used and then covered up right away," there is potential for protein-residue testing to be used on tools from an even earlier period, he said.
Daniel Stueber, one of the report's co-authors, explained that the science of protein-residue testing was adapted for archeology from forensic science, and is still a relatively underused tactic in the field.
"I think since we have these great results, it will inspire other researchers to try this method in other places," he said.
"If they have the right environment, the blood residue will be there. People have always been sort of skeptical that you can find blood residue at this antiquity, they know eight, 10, 12, 14,000, maybe 100,000, but 200,000 years – you know, more than that, people would assume that you can't find it."
Dr. Stueber is happy his team tried: "If you don't look for it, you don't know whether it's there or not," he said.
"We were just courageous enough to take the chance and test for it and we got really strong results."
The research received grant funding from the Social Sciences and Humanities Research Council of Canada, and protein tests were done at The Residue Analysis Lab of Archaeological Investigations Northwest in Portland.