Anthropologists at the University of Colorado at Boulder have discovered a groundbreaking new technique that will allow them and their colleagues around the world to study ancient human bones without destroying them.
It’s a problem that anthropologists have been grappling with for some time. Do they destroy rare bone samples from prehistoric sites in order to learn more about them or do they work to preserve them without gaining any new information that could shed light on a period of human history and development that we still don’t know a whole lot about?
One way to gather data about bones is by analyzing the bits of collagen that may still be intact, but this requires techniques that damage the bones.
“Bone collagen is really a treasure within the realm of archaeology,” Department of Anthropology graduate student Christina Ryder says.
However, once a bone is damaged or destroyed, there is no reversing it.
So, the anthropologists over at Colorado University, led by study coauthor Matt Sponheimer tried a simple “game-changer” method to analyze ancient bones using “near-infrared spectroscopy as a tool for gauging the collagen content of ground and whole bone from about 500 to 45,000 years ago.”
“These remains have lain intact for thousands of years, so it always hurts a little bit to destroy a sample,” Sponheimer said. “It’s doubly tragic if you do it, and it’s all in vain. That’s what we’re trying to prevent. My student was spending weeks and, ultimately, months of lab time trying to get dietary info from ancient collagen, and it was working incredibly poorly. I thought to myself, ‘There has to be a better way.’”
Here’s a YouTube demonstration of near-infrared spectroscopy being used to analyze plants at a zoo:
To test the “better way”, the team needed samples to work with, which they found at two different institutions, one in the United States, and the other in Germany.
According to the study published by Nature:
Extractions of collagen for ground bone specimens of Holocene age took place in the Archaeological Stable Isotope Lab at the University of Miami…Extractions of collagen for whole bone specimens of Pleistocene and Holocene age took place at the Max Planck Institute for Evolutionary Anthropology in Leipzig.
And using near-infrared spectroscopy (NIR), a simple technology, was a complete success that now gives scientists the ability to analyze many samples in a short period of time without damaging or destroying them.
For instance, sites often contain thousands of bones or fragments that might prove useful for radiocarbon, paleodietary, or paleoproteomic analyses. Even sites with relatively poor bone preservation (typically less than 1% collagen by weight) can contain specimens with reasonably intact collagen. For instance, of 50 bones analyzed from the Neanderthal site Zafarraya, three retained more than 4% collagen. Acquisition of NIR spectra takes roughly five seconds per sample, so one could scan hundreds of samples to identify these rarities in a single afternoon.
Ryder mused that “the longest part of the process is typing in the file name.”
It’s that quick and efficient, and also allows researchers to scan other parts of bones.
Another benefit of this technique would be the ability to more adequately pick specific spots of individual bones for analysis. Archaeological bone is far from homogenous when it comes to collagen preservation, yet typically only one small area is sampled to determine a bone’s suitability.
The technology could be of particular use at archaeological sites lacking collagen preservation, allowing researchers to scan and analyze rare samples to spare them from more destructive techniques.
It is easy to envision taking NIR scans of multiple spots on a bone to pinpoint areas where sampling might be most fruitful. This is likely to be of greatest importance at sites where collagen preservation is especially poor, making the identification of even a few fragments with moderate preservation crucial. At a different scale, the speed and cost effectiveness of the technique could make it easier to address questions about inter- or intra-site variation in preservation and post-depositional processes.
The technology was particularly handy in Germany, where one researcher had few samples to work with, which makes destroying them for analysis purposes a tough choice that renders few rewards.
“The grad student on this project had only six vials of samples from human burials,” Ryder said. “That was all she had, and that was all anyone was going to have for the foreseeable future.”
Overall, the team “used 50 archaeological ground bone samples of Holocene age to create our proof of concept NIR model.”
Principal component analysis (PCA) was carried out to ascertain whether or not patterns relating to collagen preservation existed in the spectral data. After it was apparent that there were clear spectral differences relating to collagen content, the data were sorted by collagen yield and the even and odd samples were assigned to the calibration and validation sets respectively.
The team isn’t saying that the technology will totally replace other methods, but it can be a very useful option in unique circumstances that will save time in the lab and identify contaminants that need to be removed.
We are not suggesting that NIR spectroscopy should supplant %N or other spectroscopic techniques for addressing the question “Does this individual specimen have sufficient collagen for analysis?” However, the results presented here suggest that this tool has significant advantages over commonly employed techniques for answering the question, “Which of the hundreds or thousands of bones at this site (or in this collection) are especially well-preserved?”
Near-infrared spectroscopy can do this form of cherry-picking quickly and inexpensively on site, and as a bonus, it should reveal environmental or conservation contaminants that must be removed for radiocarbon or isotopic paleodietary analyses. This might save weeks of lab work, not to mention considerable analytical and labor costs. Most importantly, however, with such prescreening fewer specimens would be exposed to destructive analysis.
The last, but most important aspect of this technology is that it could very well become developed enough to one day scan for and find ancient DNA, which would be incredibly useful to researchers.
“For those who do this work, the practical benefits are obvious,” Sponheimer said.
Indeed, finding DNA can help re-write human history. We can learn about how humans have moved around the world and interacted with it. We can learn about past human health and solve age-old questions that have been debated for decades, even centuries.
This new method of analyzing bones truly is exciting and gives anthropologists and other academics an opportunity to study specimens without collateral damage all while providing a future hope that it will develop into a DNA detector. That would be the real game-changer.
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