It may have given our ancestors an evolutionary edge over Neanderthals.
On a chilly night 200,000 years ago, a group of our ancestors would have huddled around a fire to rest, cook meat, and keep warm. Meanwhile, a distant group of Neanderthals likely found themselves sitting around a similar fire. The big difference is that the Neanderthals were slowly poisoning themselves with every smoky inhalation and every bite of charcoal-broiled meat.
Writing in the journal Molecular Biology and Evolution, researchers have now pinpointed a genetic mutation that may have helped modern humans adapt to smoke exposure from fires. Neanderthals and Denisovans were found to lack this mutation, and no other primates are known to have it.
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There is evidence that our hominin ancestors and Neanderthals were both capable of controlling fire. "Cooking with fire could have allowed our ancestors to incorporate a broader range of foods in our diets, for example, by softening roots and tubers that might otherwise have been hard to chew," said study co-author George Perry, from Pennsylvania State University, in a press release.
"Cooking could also help increase the digestibility of other foods, both in chewing time and reduced energetic investment in digestion."
Fire was also a source of warmth, and hunter-gatherers regularly burned vegetation as a landscape management tool.
The problem with using all that fire is that it produces toxic materials, such as dioxins and polycyclic aromatic hydrocarbons, which at high concentrations can lead to respiratory infections. Exposure of pregnant females to these toxins can increase the chance of infant mortality.
The mutation that the researchers identified may have desensitized ancient humans to some of these toxins.
"If you're breathing in smoke, you want to metabolize these hydrophobic compounds and get rid of them, however, you don't want to metabolize them so rapidly that it overloads your system and causes overt cellular toxicity," said senior author Gary Perdew.
"The evolutionary hypothesis is, if Neanderthals were exposed to large amounts of these smoke-derived toxins, it could lead to respiratory problems, decreased reproductive capacity for women and increased susceptibility to respiratory viruses among preadolescents, while humans would exhibit decreased toxicity because they are more slowly metabolizing these compounds," he explains.
But over time, those benefits have yielded negative side effects. Perdew suggests that the the mutation might give humans a better tolerance for cigarette smoke, simultaneously allowing people to take up smoking and putting them at risk of cancer and other disease.
"Our tolerance has allowed us to pick up bad habits," Perdew says.
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