A long-term health decline—including a gradual shrinking—among prehistoric Indians in California may be linked to their everyday use of tar, which served as "superglue," waterproofing, and even chewing gum, scientists say.
Naturally occurring polycyclic aromatic hydrocarbons (PAHs) in bitumen tar could at least partially explain a decrease in skull size over a period of about 7,500 years in the Chumash people, a recent study proposes. Decreased head size usually reflects decreased stature - a biological indicator of a population's declining health.
The Chumash lived in dense villages of up to 20,000 people in the Channel Islands (see map) and used shell beads as currency. The hunter-gatherers collected tar from the plentiful natural seeps on the islands and used the gummy substance for everything from building canoes to casting broken bones to making chewing gum.
Though the PAHs in bitumen are known toxins, "this is a health risk that no one has brought up" in the context of the Chumash, said study co-author Sabrina Sholts, an anthropologist at the University of California, Berkeley. The decline "we're talking about is a very gradual process over thousands of years, and it could have been the chemicals, these carcinogens [the Chumash were] exposed to everyday."
In the modern world, PAHs are widespread as byproducts of fossil fuel combustion, cigarette smoking, road paving, and roofing. Previous research has shown the chemicals are easily taken up by the human body through breathing, ingestion, or skin contact—and can be distributed to organs, tissues, and fetuses.
While analyzing skeletons of 269 Chumash males and females from various periods, the team found a marked decrease in skull size over time, according to the research (May, Journal Environmental Health Perspectives.)
The researchers tested modern tar from seeps in ancestral Chumash territory. The tar turned out to have high levels of toxic PAHs.
Next, the team examined previous studies about how PAHs enter the human body.
For instance, the Chumash would have literally drunk PAHs, since bitumen was used to waterproof tightly woven fiber baskets that served as water bottles.
The Chumash not only used the tar regularly, they used it more and more as the years went by, based on increasing levels of bitumen found in artifacts.
The Chumash began building canoes with multiple wooden planks about 1,500 to 2,000 years ago, noted archaeologist Lynn Gamble. Tar was used to seal any spaces where the planks met and to plug holes, as well as as an adhesive in a canoe's body and paddles, said Gamble, of the University of California, Santa Barbara.
Despite the bitumen evidence, study co-author Sholts said, "the most significant health impact experienced by the population was contact with Europeans." Beginning in the 1700s, the new arrivals moved many Indians into Spanish missions on the mainland. There, many Chumash died from diseases and mistreatment.
Sholts also emphasized that that there's no established way to test for hydrocarbons in ancient bones. The link between PAHs and bone change is "somewhat speculative—To actually target PAHs more specifically, we need to do a biochemical analysis of bone."
The Chumash tar-use study is more than a history lesson. Examining PAH exposure's long-term effects in a past population can help scientists understand the chemical's toxicity today, study co-leader Sholts said.
"Currently the effects of modern PAH exposure—most significantly from major accidents such as the Gulf oil spill—are not fully understood," she said. "This is a great example of how studies of ancient human remains can shed light on contemporary problems."
For much more, read the article at news.nationalgeographic.com.Thanks for coldrum for the link.
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