Ancient lead exposure shaped human evolution

An international study has challenged the view that exposure to lead is largely a post-industrial phenomenon, revealing that our human ancestors were periodically exposed to lead for over two million years — and that the toxic metal may have influenced the evolution of hominid brains, behaviour, and even the development of language. The study also adds a piece to the puzzle of how humans outlived their cousins, the Neanderthals.

Published in the journal Science Advances, the research combined fossil geochemistry, brain organoid experiments and evolutionary genetics to uncover a surprising story about lead’s role in human history. It was led by researchers from the Geoarchaeology and Archaeometry Research Group (GARG) at Southern Cross University (SCU), the Department of Environmental Medicine at the Icahn School of Medicine at Mount Sinai Hospital, and the School of Medicine at the University of California San Diego.

A toxic thread through human evolution

Lead has been woven into human society for thousands of years — from the plumbing systems of the Roman Empire to the paints, pipes and industrial alloys still in use today — but scientists have generally accepted lead exposure as a largely modern phenomenon. Now, by analysing 51 fossil teeth from hominid and great ape species, including Australopithecus africanus, Paranthropus robustus, Neanderthals and Homo sapiens, the team discovered clear chemical signatures of intermittent lead exposure stretching back almost two million years.

Using high-precision laser-ablation geochemistry at SCU’s GARG facility and Mount Sinai’s Exposomics facilities, the researchers found distinctive ‘lead bands’ in the teeth, formed during childhood as the enamel and dentine grew. These bands reveal repeated episodes of lead uptake from both environmental sources (such as contaminated water, soil or volcanic activity) and from the body’s own bone stores, released during stress or illness.

“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 SCU’s GARG research group.

“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.

“Our work not only rewrites the history of lead exposure, 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.”

Lead and the language gene

The team also turned to the lab to explore how this ancient exposure might have affected brain development. Using human brain organoids, they compared the effects of lead on two versions of a key developmental gene called NOVA1, a gene known to orchestrate gene expression upon lead exposure during neurodevelopment. The modern human version of NOVA1 is different from that found in Neanderthals and other extinct hominids, but until now, scientists did not know why this change evolved.

When organoids carrying the archaic NOVA1 variant were exposed to lead, they showed marked disruptions in the activity of FOXP2 — expressing neurons in the cortex and thalamus — brain regions that are critical for the development of speech and language. This effect was far less pronounced in organoids with the modern NOVA1 variant.

“These results suggest that our NOVA1 variant may have offered protection against the harmful neurological effects of lead,” said Professor Alysson Muotri, 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.”

Genetic and proteomic analyses in this study further revealed that lead exposure in archaic-variant organoids disrupted pathways involved in neurodevelopment, social behaviour and communication. The altered FOXP2 activity in particular points to a possible link between ancient lead exposure and the evolutionary refinement of language abilities in modern humans.

“This study shows how our environmental exposures shaped our evolution,” said Professor Manish Arora, Vice Chairman of Environmental Medicine at the Icahn School of 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.”

Lead exposure still endangers children today

The findings underscore how deeply intertwined environmental toxins and human biology have been, and warn that our vulnerability to lead may be an inherited legacy of our past. Indeed, a separate international study published in the journal Communications Earth & Environment has found that lead exposure remains a serious global health issue today, with children in low- and middle-income countries bearing the brunt.

The introduction of tetraethyl lead into petrol (or gasoline) in the 1920s was particularly destructive for human health, spewing millions of tonnes of the metal into the atmosphere for the next several decades. By the 1970s, children across the world carried dangerously high blood lead levels, resulting in neurological damage, impaired development and countless premature deaths.

The eventual ban on leaded petrol, completed worldwide only in 2021, is heralded as one of the great public health victories of the modern era. However, the research team says the celebration of a ‘lead-free’ world was premature: while blood lead levels fell in many high-income countries, they plateaued or even rose again in parts of Asia, Africa and Latin America. Legacy contamination from soils and infrastructure, coal combustion, lead-laden products such as leaded paint, and informal recycling of lead-acid batteries and e-wastes have all kept exposure alive.

“The perception that the problem was solved has to change,” said study leader Dr Chen Mengli, a Research Fellow at the National University of Singapore (NUS). “New sources of exposure continue to emerge and the historical emitted lead keeps redistributing through various natural processes.”

Lead production today exceeds 16 million tonnes a year, with about 85% going into lead–acid batteries that power vehicles, telecommunications and backup energy systems. Annual production now exceeds the total lead emitted during the entire era of leaded petrol.

Though these items can be recycled, much of the reprocessing occurs under unsafe conditions, particularly in low- and middle-income countries. Informal recycling sites, often located near homes and schools, expose workers and surrounding communities to hazardous levels of lead. Coal combustion, contaminated soils and the continued sale of lead-laden paints, toys and even food products further compound the risks.

According to the literature, the health consequences are most severe for children. Even at low levels, lead can damage the developing brain, lowering IQ, impairing learning and contributing to behavioural issues. This burden is often carried across one’s lifetime as the effects are irreversible. In particular, the team estimated that childhood exposure today translates into a global economic loss exceeding US$3.4 trillion annually, equivalent to over 2% of the world’s GDP.

Four-pronged approach to curb a resurgence

The team highlighted that recognising the continuing risks is the first step towards preventing another global health crisis. Their study outlines four urgent areas for action to safeguard public health and reduce inequality:

• Manage the life cycle of lead-containing products. With demand for batteries and electronics rising, stronger oversight is needed to minimise leakage during production, use and disposal.
• Eliminate unsafe and illicit sources. Informal recycling and lead-laden goods such as lead paints, glazed ceramics and adulterated spices continue to expose millions to hazardous levels of lead.
• Strengthen monitoring and community involvement. Early detection of lead leakage is often underfunded. Advances in low-cost sensors and machine-learning-based tools, combined with local knowledge, can help identify and address hotspots more effectively.
• Capture the full socio-economic cost. Lead exposure disproportionately harms disadvantaged populations. Better models and population-level data are needed to quantify long-term impacts on health, education and productivity, as well as guiding equitable policy responses.
   

“The world rightly celebrated the phase-out of leaded gasoline as a triumph of international cooperation,” Chen said. “But the problem of lead exposure has not yet gone away. Unless we remain vigilant about both new sources of exposure and the legacy of lead in the environment, we may risk repeating the same tragedy.”

Image caption: Using portable aerosol samplers, Chen’s team collected air samples near a brick kiln. They also gathered samples from various locations, from busy city streets to remote oceans, to capture the current level of lead pollution. To trace the past, they turned to natural archives like peat bogs and coral cores, whose layers reveal how lead pollution has changed through history. Image credit: Dr Reshmi Das.