A long-term health decline among prehistoric Indians in California (USA) may be linked to their everyday use of tar, which served as glue, waterproofing, and even chewing gum.
     The Chumash lived in dense villages of up to 20,000 people in the Channel Islands 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. While analysing skeletons of 269 Chumash males and females from various periods, a team of anthropologists found a marked decrease in skull size over time, according to the research, published in May in the journal Environmental Health Perspectives.
     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, the recent study proposes. Decreased head size usually reflects decreased stature, which is a biological indicator of a population's declining health.
     PAHs in bitumen are known toxins - byproducts of modern fossil fuel combustion, cigarette smoking, road paving, and roofing. The chemicals are easily taken up by the human body through breathing, ingestion and skin contact, and can be distributed to organs, tissues, and foetuses. Major health problems - including cancer, altered hormone levels, and damage to internal organs - have been connected to PAH exposure.
     Modern tar from seeps in ancestral Chumash territory have high levels of toxic PAHs. 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 artefacts.
     Bitumen was used to waterproof tightly woven fibre baskets that served as water bottles. The Indians also heated the tar to make it more malleable, producing fumes that could have easily been inhaled. Tar was also used as an adhesive in bone whistles, flutes, shell containers, abalone dishes, the mouthpieces of smoking pipes, and musical rattles. Women wore grass skirts weighted with bits of tar. They began building canoes with multiple wooden planks about 1,500 to 2,000 years ago, using tar to seal any spaces where the planks met, to plug holes, and as an adhesive in a canoe's body and paddles.
     In general, the study presents "an intriguing idea - it certainly deserves more research," said noted archaeologist Lynn Gamble, of the University of California, Santa Barbara.

Edited from National Geographic News (6 October 2011)