The notion that modern humans outcompeted Neanderthals due to their greater resistance to toxic smoke components from fire has been a subject of debate among scientists. A previous study had proposed that modern humans were better protected against the harmful effects of smoke, a suggestion that has now been challenged by new genetic research. This fresh study, published in Molecular Biology and Evolution on November 24, 2024, undermines the idea that the differences in fire tolerance played a pivotal role in the survival of modern humans over Neanderthals.
Fire-making is considered one of the most significant milestones in human evolution, providing warmth, protection from predators, and the ability to cook food. While fire dramatically expanded early human diets by making otherwise inedible foods safe to consume, it also comes with potential risks. The toxic substances produced by smoke can have harmful effects on the body, particularly the respiratory and immune systems. However, because traces of fire rarely preserve well in the archaeological record, the timing of when early humans and Neanderthals mastered fire remains unclear, and the extent to which both species were exposed to its dangers is still a topic of investigation.
In 2016, two opposing genetic studies examined the ability of modern humans and Neanderthals to tolerate these toxic smoke compounds. One study, led by a group of American scientists, focused on the aryl hydrocarbon receptor (Ah receptor), a protein that responds to toxic substances found in smoke. They concluded that Neanderthals were up to a thousand times more sensitive to these toxic substances than modern humans, suggesting that fire may have played a detrimental role in their decline. In contrast, another study, led by researchers from Leiden University and Wageningen University & Research, found evidence that Neanderthals had genetic variants in 19 different genes that might better neutralize the harmful effects of smoke compared to most modern humans. These genetic variants were primarily older in evolutionary terms, indicating that Neanderthals might have had a greater natural resistance to the toxic effects of fire.
The new research, led by molecular biologists Jac Aarts and Wil Roebroeks from Leiden University, directly challenges the earlier American study. Their team repeated the experiment using an improved research design that utilized human cells, as opposed to the rat cells used by their predecessors. Additionally, Aarts and his colleagues scrutinized the Ah receptor protein more carefully by analyzing the complete and original genetic data for both human and Neanderthal versions of the protein. Their findings revealed that there was no evidence to support the claim that Neanderthals were more vulnerable to smoke toxins than modern humans. The new data showed no significant difference in the functionality of the Ah receptor between the two species.
This new analysis is particularly significant because it provides a better understanding of the role that fire played in early human biology. The study emphasizes the importance of studying proteins in their relevant biological context—meaning in actual human cells—rather than relying on animal models or less direct approaches. This method ensures that conclusions are more aligned with human biology and genetics, providing a clearer picture of how both modern humans and Neanderthals might have interacted with their environment.
The implications of this study extend beyond the debate on Neanderthal extinction. The research contributes to a broader understanding of how early hominins, including Neanderthals and other human ancestors, interacted with fire. Previous studies in Leiden have shown that early hominins likely survived in Europe for thousands of years without fire, making fire an even more crucial tool once it was adopted. In 2018, Leiden archaeologists were the first to demonstrate that early hominins had indeed mastered the use of fire, a discovery that significantly reshaped our understanding of human evolution. Furthermore, the research on fire use is gaining relevance today as wildfires in regions like Australia and America have become more frequent and destructive, underlining the ongoing importance of fire in shaping both human history and contemporary ecological landscapes.
In conclusion, the new findings challenge previous assumptions about Neanderthal vulnerability to toxic smoke and underscore the importance of studying ancient human biology through more refined, human-specific methods. The research not only refines our understanding of the role of fire in human evolution but also highlights the critical need for contextual biological studies to understand how ancient humans adapted to their environments. This research serves as a reminder of the complexity of human evolution and the many factors—biological, environmental, and technological—that shaped the survival of modern humans and the extinction of Neanderthals.
Source: Leiden University