Most archeologists are content to dig up pottery, bones and other relics of the past. Thomas H. Loy takes a different approach--he analyzes ancient blood.
Loy, of the Australian National University in Canberra, has developed a technique for literally lifting minute splotches of blood off stone tools and bones. Not only does the blood possess features that identify what species of animal it came from, but it can be used to date artifacts up to 50,000 years old. Researchers may even be able to extract bits of genetic material from prehistoric blood that will provide insights into human evolution.
Loy introduced his technique of blood residue analysis to the scientific world in 1983. In his laboratory, he studied 104 stone tools unearthed in British Columbia that range in age from 600 to 1,000 years and found blood deposits on nearly all of them. The blood belonged to a variety of animals, he reported, including blacktailed deer, moose, snowshoe rabbits, caribou and grizzly bears. A few of the younger artifacts contained human blood.
Since then, he has taken blood residue analysis out of the lab and into the field. At a 10,000-year-old farming village in Turkey, Loy and Andree R. Wood of the University of Chicago recently extracted the blood of humans, sheep and an extinct type of cattle from a stone slab near the entrance of a structure ominously known as the "skull building."
Rooms in the rear of the skull building in the Turkish village of Cayonu Tepesi contained more than 90 human skulls and the remains of several human skeletons.
"We don't know exactly what was going on in the skull building, but human and animal blood was abundant on the slab," Wood said. The occasional cutting up of humans and animals, for whatever reasons, may have taken place there, she added.
The grisly practice of human sacrifice is one possibility, but bodies may have been carted to the skull building after death and placed on the slab for some type of ritual before burial. The skeletal remains in the back of the building may have come from individuals placed on the slab, although there are no decapitation marks at the base of the skulls.
Whatever purpose the skull building served, Loy's blood analysis demonstrates that people living in one of the world's earliest known farming villages had surprisingly complex cultural practices. This suggests that the village had existed for some time prior to 10,000 years ago, which in turn strengthens the notion that humans crossed the threshold from hunting and gathering to a farming life considerably earlier than many had believed.
The process of studying ancient blood begins by locating dark patches of suspected blood with a low-power microscope. The samples are analyzed with a coated paper strip sensitive to hemoglobin in the blood. Confirmed blood deposits are scraped off and subjected to a chemical process that crystallizes hemoglobin. The size and shape of hemoglobin crystals differ among animal species, allowing researchers to identify what type of beast spilled the blood. To further check the results, hemoglobin is placed in a gel and exposed to an electric field; its molecules then line up in patterns that correspond to specific animal species.
If the blood appears to be from a human being, it is tested for the presence of human immunoglobulin, which aids in the body's defense against disease.
At Cayonu Tepesi, Loy and Wood isolated human and sheep blood on the stone slab, but were puzzled by the presence of another type of blood from an unknown, nonhuman species. They lifted blood from bone fragments of an extinct cattle species discovered at the site and found that its hemoglobin crystals matched those of the unknown species taken from the slab. This is the first time the blood of an extinct animal has been identified, Loy said.
Further excavations in the skull building uncovered several skulls and horns belonging to the same extinct form of cattle. Loy and Wood also found a large flint knife containing traces of cattle and human blood. The knife may have been used in human sacrifices or mortuary rituals, but Loy noted that human blood often ends up on stone tools when toolmakers accidentally cut their fingers while adjusting an edge.
Minute quantities of blood taken from the skull building's slab were also placed in a machine that separates and counts carbon atoms of different mass. The decay of specific carbon atoms in the samples allowed Loy and Wood to calculate that the blood is about 9,000 years old. Carbon dating is typically used with charcoal and is considered accurate back to about 50,000 years ago.
In another study, Loy found that blood can survive on stone for much longer than 9,000 years, or even 50,000 years. A stone tool from a site in Iraq that dates to between 75,000 and 125,000 years ago yielded human blood that Loy originally thought came from a Neanderthal.
However, further analysis indicated that the hemoglobin crystals in the prehistoric blood were comparable to those of modern humans, Loy said. He acknowledged that it is unclear now which species left behind the blood on the stone tool.
Neanderthals and modern humans inhabited the Near East at around the same time, but the bulkier Neanderthals became extinct around 35,000 years ago.
Many anthropologists contend that modern humans--who are considered modern because of shared changes in the anatomy of the skull and lower body--originated in Africa and rapidly spread throughout the world around 200,000 years ago, driving Neanderthals to extinction in the process. Others argue that modern humans originated nearly 1 million years ago in several regions of the world and interbred to some extent with Neanderthals.
One way to help resolve the debate is to study the genetic material, or DNA, of Neanderthals and modern humans for evidence of chemical similarities or differences, Loy said. He and his colleagues plan to extract and analyze DNA from the ancient Iraqi blood using the techniques of modern DNA fingerprinting, which rely on enzymes that chop up DNA into distinct patterns.
In addition, a method developed by British researchers to extract DNA from bone could enable scientists to compare the chemical makeup of DNA from Neanderthal and modern human fossils. Similarities would point to a shared genetic heritage between Neanderthals and ourselves.
If such studies are conducted, confirmed samples of Neanderthal DNA can be compared to DNA taken from the Iraqi blood sample, Loy noted.
Beyond disputes over human evolution, blood residue analysis also has the potential to clarify the history of specific diseases, according to Loy. The human body contains a library of antibodies formed to fend off particular illnesses. Those antibodies can be isolated from ancient blood samples and researchers can determine the ailments afflicting people who died thousands, or tens of thousands, of years ago.
Yet archeologists are not clamoring to conduct independent blood analyses and DNA studies on prehistoric stones and bones, Loy lamented, because they simply are not trained in the new techniques.
Moreover, the blood of Neanderthals and even earlier members of the human evolutionary family undoubtedly stains some of the millions of stone tools lying in the museums of the world. "There's a tremendous blood bank on ancient stone tools just waiting to be studied," Loy said.