Ancient Homo sapiens and Neanderthals encountered levels of lead exposure that were not believed to have existed until the Industrial Revolution, altering how our brains evolved, say an international team of researchers.
For two million years of human existence, lead exposure may have impacted everything from behavior to speech, driving a gradual separation between Homo sapiens from Neanderthals. According to the new findings, Homo sapiens may have held the competitive edge in mitigating lead toxicity as the species vied for dominance long ago when both hominin species occupied the planet.
Ancient Human Brains
Exploring the ancient brains of both species required an interdisciplinary approach combining fossil geochemistry, organic experiments, and evolutionary genetics. Before this research, the standard view was that humans did not commonly experience high levels of lead exposure before relatively modern activities such as mining, smelting, and the production of lead-based materials like paint.
Contrary to this assumption, fossil analysis revealed an unexpected discovery: 51 fossilized teeth displayed chemical signatures indicating intermittent lead exposure as far back as two million years ago. Laser ablation geochemistry revealed that lead bands formed in the teeth, beginning in childhood, while the enamel and dentine were still growing.
The teeth came from a variety of species, which, in addition to Homo sapiens and Neanderthals, included early varieties of Homo, Australopithecus africanus, and Paranthropus robustus, illustrating the widespread exposure. Likely sources for the lead included environmental factors, such as contaminated water or soil, as well as lead released from bones during illness or stress.
“Our data show that lead exposure wasn’t just a product of the Industrial Revolution – it was part of our evolutionary landscape,” said Professor Renaud Joannes-Boyau, Head of the GARG research group at Southern Cross University. “This means that the brains of our ancestors developed under the influence of a potent toxic metal, which may have shaped their social behaviour and cognitive abilities over millennia.”
Recreating the Neanderthal Brain
Moving over to genetics, the researchers then explored how the lead exposure findings could have impacted brain development by looking at differences in a neurodevelopmental gene called NOVA 1, which is essential for gene expression under lead exposure during neurodevelopment. Before this research, notable differences between NOVA1 in modern humans compared to Neanderthals and early modern hominins had remained unexplained.
The team constructed miniature organic models of human brains called organoids; some contained the modern NOVA1 variant, while others contained the archaic variant. After exposing both models to lead, clear differences emerged. In organoids with the archaic variant, FOXP2 neurons in the cortex and thalamus exhibited significantly greater disruptions compared to those with the modern variant. These regions are heavily associated with speech and language development.
“These results suggest that our NOVA 1 variant may have offered protection against the harmful neurological effects of lead,” said Professor Alysson Muotri, Professor of Pediatrics/Cellular & Molecular Medicine and Director of the UC San Diego Sanford Stem Cell Institute Integrated Space Stem Cell Orbital Research Center.
“It’s an extraordinary example of how an environmental pressure, in this case, lead toxicity, could have driven genetic changes that improved survival and our ability to communicate using language, but which now also influence our vulnerability to modern lead exposure,” he added.
Environmental and Genetic Health
“This study shows how our environmental exposures shaped our evolution,” said Professor Manish Arora, Professor and Vice Chairman of Environmental Medicine. “From the perspective of inter-species competition, the observation that toxic exposures can offer an overall survival advantage offers a fresh paradigm for environmental medicine to examine the evolutionary roots of disorders linked to environmental exposures.”
Despite our resilience compared to Neanderthals, lead exposure remains a significant health risk in the modern world, primarily due to industrial activities. Maintaining an awareness of how connected our environment and biology can be is an essential lesson of the discovery, the researchers say.
“Our work not only rewrites the history of lead exposure,” added Professor Joannes-Boyau, “it also reminds us that the interaction between our genes and the environment has been shaping our species for millions of years, and continues to do so.”
The paper, “Impact of Intermittent Lead Exposure on Hominid Brain Evolution,” appeared in Science Advances on October 15, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.