**Lead Exposure and Human Evolution: What Ancient Teeth Reveal**
Fossilized human teeth spanning two million years of evolution have been studied for their lead content—and the results were surprisingly high. To understand how lead affected the human brain both then and now, researchers created brain organoids carrying ancient and modern variants of a gene essential for brain development.
When exposed to lead, organoids with the ancient gene variant suffered significant dysfunction, including impairment of another gene involved in speech and language. This discovery suggests that while Homo sapiens gained an evolutionary edge over human ancestors such as Neanderthals through larger brains, we may also have benefited from a gene variant that offered protection against lead poisoning.
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### The Ubiquity of Lead in the Environment
Lead is a well-known neurotoxin and can be lethal. While modern products like makeup, paint, and piping have been reformulated to eliminate lead, this harmful element has existed in nature long before humans started manufacturing. Lead naturally occurs in rocks, soils, sediments, and bodies of water.
Certain environmental processes—such as volcanic eruptions, wildfires, erosion, and surface layer stripping—can release dangerous amounts of lead into the environment. Waterways and areas where water accumulates after rain or floods are especially vulnerable to lead contamination.
Lead can also accumulate in minerals that crystallize from water or magma and is stored in the bones and teeth of animals—even long after death. Tooth enamel, in particular, is stable enough to retain lead for extended periods, making it a valuable resource for studying ancient lead exposure.
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### What Ancient Teeth Tell Us
An international team of researchers examined the teeth of 51 ancient human ancestors from Africa, Asia, Oceania, and Europe, covering a period of over two million years. These specimens included hominids (all human ancestors) and hominins (specifically members of the Homo and Pan species).
Remarkably, 73% of the tested fossils showed positive results for lead contents. Even an 8-million-year-old fossil of the extinct ape *Gigantopithecus blacki* contained lead levels comparable to those associated with modern anthropogenic lead exposure from materials and factories.
The severity of this exposure signals that lead might have had a significant impact on the brains of these ancient species. According to the researchers, lead exposure was widespread throughout primate evolution and even more pervasive among hominids—not just a product of recent human industrial activity.
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### Investigating Lead’s Effects on Brain Development
To explore the impact of lead on the brain, researchers cultivated brain organoids in the lab. These primitive brain models, derived from stem cells, contained either ancient or modern variants of the NOVA1 gene—a gene responsible for producing an RNA-binding protein essential for mammalian brain development and neuromuscular control.
When laboratory-grown brain tissues were exposed to lead, organoids with the ancient NOVA1 variant showed dysfunction in the FOXP2 gene. FOXP2 plays a crucial role in controlling other genes related to speech and language capabilities.
Importantly, the ancient NOVA1 variant was less effective at protecting neurons from lead-induced stress compared to the modern variant. Because modern humans developed more advanced communication skills, they were likely better equipped to warn others when something was wrong—a factor that may have contributed to the survival advantage of Homo sapiens over other hominins.
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### The Evolutionary Edge of Modern Humans
Language is a defining feature that modern humans had over Neanderthals and Denisovans. This ability may have been critical to survival.
The researchers propose that lead exposure affected neurosocial pathways—such as group-level social cohesion—and that the modern NOVA1 variant helped protect these pathways. Consequently, this genetic edge may have given Homo sapiens a relative advantage in coping with environmental toxins, influencing evolutionary outcomes.
“While we acknowledge that primate species have various social behaviors, this finding bolsters our proposition that lead exposure played a noteworthy role in their evolution by affecting neurosocial pathways, providing a relative survival advantage to modern humans over Neanderthals,” the study authors wrote.
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### Controversies and Considerations
The findings have sparked debate among scientists. Critics argue that the conclusions are speculative due to the limited number of fossils analyzed and the vast timespan involved, which may not account for the full diversity of human ancestors.
Nevertheless, if there is one trait modern humans distinctly had that Neanderthals and Denisovans lacked, it was complex language. This skill could very well have made the difference between life and death in challenging environments—with lead exposure acting as a subtle but significant evolutionary pressure.
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**References:**
The full research study detailing these findings was recently published in *Science Advances*.
https://www.popularmechanics.com/science/a69082783/ancient-human-lead-poisoning/