After years studying the Baka pygmy people of Cameroon, Fernando Ramirez Rozzi was surprised when he detected a sudden drop in fertility among young women in 2011. As he analyzed data on birth rates over a decade, Ramirez Rozzi tried to remember what had happened in the community in southeastern Cameroon that could have caused the change. The biggest news was a bar that opened in late 2010 in the heart of Moange-le-Bosquet village, selling a cheap, dangerous mix of methanol and ethanol. Since then, the bar had displaced the Catholic mission as the village’s “center of gravity,” and men, women, and even small children were sipping on $0.09 bags of booze there many nights.
But was alcohol to blame for the decline in births? To answer that question, Ramirez Rozzi, a human paleontologist at the French national research agency CNRS’s Molecular Anthropology and Synthesis Imaging Laboratory in Paris, compared the number of births before and after the bar opened.
In nomadic hunter-gatherer societies, where most people give birth in their camps, birth and death records are rare. Ramirez Rozzi, however, was lucky enough to have access to records of births since 1980 kept on index cards by nuns at the Catholic mission’s medical center in Moange-le-Bosquet, where more than 800 Baka now live in scattered settlements.
Between the nuns’ archive and his own data on family sizes, collected in the field from 2007 to 2017, Ramirez Rozzi found that the total fertility rate in Baka women for the whole period was relatively high—about seven babies on average over the reproductive lifetime of a woman. But the fertility rate dropped significantly after 2011—from an average of 8.8 babies per woman from 2007 to 2010 to 5.6 babies per woman from 2011 to 2016. And the rate plunged even more—by half—in younger women. For example, the rate among women ages 15 to 25 in the same time period.
Alcohol—especially the dangerous mix sold at the new bar run by a Bantu-speaking woman—has been shown to contribute to many serious health conditions, including infertility in women. Indeed, government authorities in Cameroon have banned the manufacture of the kind sold at the new bar because it causes major disorders of the nervous system, cancers, and death. (Since 2011, alcohol poisoning has been a leading cause of death among the Baka.) It is also associated with poor semen quality in men, Ramirez Rozzi says. That the drop in fertility was especially high among young women also pointed to alcohol as the culprit, because they generally hung out at the bar more than older women, listening to loud music and getting drunk.
Finally, Ramirez Rozzi looked into other major changes, such as higher rates of disease, that could explain the reduction in fertility. He found nothing. So he concludes that alcohol is to blame, in a paper released today in the Proceedings of the National Academy of Sciences. The data provide a “first-hand record of the impact of alcohol on fertility in a hunter-gatherer society which appears to be seriously compromising the survival of the Baka,” Ramirez Rozzi writes.
Other researchers say Ramirez Rozzi’s argument is convincing. “The case for alcohol abundance causing a drop in fertility is persuasive,” says Nicholas Blurton-Jones, professor emeritus at the University of California, Los Angeles. Blurton-Jones was not involved with the new work, but he has studied another group of hunter-gatherers, the Hadza, who also struggle with alcohol when they settle in towns.
The drop in fertility could threaten the Baka people’s chances of survival over time, Ramirez Rozzi says. And it could impact infant and child mortality: Even small children and infants suck on the drops of alcohol they find in discarded plastic bags on the ground, Ramirez Rozzi says.
When Ramirez Rozzi shared his data with the Baka women in a meeting last year, they told him that men returning from work in the fields would spend their coins on alcohol and arrive home drunk—and that young women also were drinking, and having more trouble getting pregnant. “They were very, very concerned when we told them about these fertility rates,” he says.