About 250,000 years ago, Stone Age human relatives butchered a bunch of animals with stone tools and didn’t wash up afterwards. Now scientists have analyzed the gunk crusted to the tools and figured out what was on the menu.
“We were really excited by the antiquity of the residue,” said April Nowell, an anthropology professor at the University of Victoria and lead author of the research published online today in the Journal of Archaeological Science.
She said the variety of animals butchered there suggests the people using the site had a lot of knowledge about the resources available in the area at different times of year and were socially sophisticated.
Newell took part in an archeological dig in the area called Shishan Marsh, which was an oasis in the desert used by many animals and prehistoric humans between 220,000 and 300,000 years ago. Geological and plant-based evidence shows it was originally a lake surrounded by lush vegetation, but over several thousand years became “as arid or more arid than today.”
That made it a “challenging” environment for the Stone Age nomadic hunter-gatherers who used it, Nowell said.
“They’re definitely pre-modern humans,” she added. They likely belonged to the species Homo erectus or Homo heidelbergensis.
None of their remains have been found at the site and the researchers don’t think they lived at the oasis — they simply visited to forage for food and water. In the process, they left behind stone tools used for hunting, scavenging and butchering meat, such as spearheads or arrowheads, scrapers, knives and hand axes.
Some were larger tools made from stone found further away and likely brought with them. Others were smaller ones made from local pebbles.
The researchers excavated about 10,000 tools in all, and found protein residue on 17 of them.
In order to identify the proteins, the researchers exposed them to immune system antibodies, mostly produced from goat blood, designed to recognize different types of animals. The tools tested positive for horse, camel, cow, rhinoceros and duck blood, but not cat or goat.
The researchers say it’s the first time this technique has been used to identify protein residues on such old stone tools. They’re now working on making antibodies that can recognize elephant and ostrich so they can test for those in the future, Nowell said.
Scientists have previously found other evidence suggesting what Stone Age humans ate – generally animal remains featuring cut marks or signs of burning, such as a 400,000-year-old prehistoric meal of roast tortoise found in a cave in Israel and reported earlier this year.
However, protein residues are more direct evidence of what people were eating, Nowell said. They can also preserve evidence of types of animals whose fragile bones don’t preserve well, such as birds, or evidence at sites where animal remains in general don’t preserve well.