Behavioral Ecology of Tobacco and Cannabis Use Among Aka Foragers of the Congo Basin
Roulette, Casey Jordan
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Little is known about substance use among extant hunting-gathering populations. I therefore conducted one of the first biocultural, and biomarker validated, studies of tobacco and cannabis among the Aka foragers of the Congo Basin. Because tobacco and cannabis contain anthelmintic compounds, and because the Aka suffer from high rates of helminthiasis, I also tested a hypothesis that recreational use of neurotoxic plants helps defend against parasites. Self- and peer-reports of tobacco and cannabis were collected from all Aka residing in the study area (n=379). Detailed questions about substance use were asked among a subset of these. Because female use was low, I restricted saliva, urine and stool sample collections to men. Saliva samples were assayed for cotinine, a nicotine metabolite; urine samples were assayed for THCA, a metabolite of THC; a subsample was genotyped for the CYP2A6 enzyme, which metabolizes nicotine. Stool samples were assayed for intestinal helminth eggs as an index of worm burden. Aka men pay more for tobacco, yet have a higher smoking prevalence (95%) than men in most other populations, whereas Aka women have a low prevalence. Aka thus have one of the largest known gender differences in smoking. Tobacco is widely shared, and might play a central role in this defining aspect of Aka culture. Significant negative correlations between cotinine and worm burden and THCA and worm burden were found. Treating helminths with a commercial anthelmintic reduced cotinine concentration two weeks later, compared to placebo controls. Significant negative rank correlations were found between year 1 cotinine concentrations and reinfection by year 2 and between year 2 THCA concentrations and reinfection. Finally, younger and older participants with slow nicotine-metabolizing alleles had lower worm burdens compared to those with extensive metabolizing alleles. Tobacco advertising cannot easily explain the high prevalence of smoking among Aka men, nor can socioeconomic disparities, proscriptions, or the addictiveness of nicotine easily explain the low prevalence among Aka women. Aka smoking might be better explained by internal, rather than external, cultural and political-economic factors. In addition, these results provide the first support for the hypothesis that substance use helps defend against parasites.