Human ancestors faced leadership millions of years ago, and it shaped our evolution

When we think of lead poisoning, most of us imagine modern man-made pollution, paint, old pipes, or exhaust fumes.

But our new study, published today in Science advancesreveals something far more surprising: Our ancestors faced leadership for millions of years, and it helped shape the evolution of the human brain.

The discovery suggests that the toxins we fight today have been intertwined with the story of human evolution since its inception.

It reshapes our understanding of both the past and the present, tracing a constant thread between ancient environments, genetic adaptations, and the unfolding evolution of human intelligence.

A poison older than humanity itself

Lead is a potent neurotoxin that disrupts the development and function of both the brain and body. There is no safe level of lead exposure, and even small traces can impair memory, learning, and behavior, especially in children. This is why eliminating lead from gasoline, paint, and plumbing is one of the most important public health measures.

Yet while analyzing ancient teeth at Southern Cross University, we uncovered something completely unexpected: clear traces of lead in the fossils of early humans and other ancestral species.

These samples, recovered from Africa, Asia and Europe, were up to 2 million years old.

Using lasers longer than a stand of hair, we scanned each tooth layer by layer—like reading the growth rings of a tree. Each band recorded a short chapter in the individual’s life. When lead enters the body, it leaves a clear chemical signature.

These signatures revealed that the exposure was not rare or accidental. This happens repeatedly over time.

Where did this lead come from?

Our findings suggest that early humans were never spared the leadership of the natural world. On the contrary, it was also a part of their world.

The advantage we got wasn’t from mining or smelting—those activities are relatively recent in human history.

Instead, it came from natural sources such as volcanic dust, mineral-rich soil and groundwater flowing through lead-bearing rocks in caves. In times of drought or food shortages, early humans may have dug for water or eaten plants and roots that absorbed lead from the soil.

The fossil tooth we study is a record of survival. A small diary of a person’s early life written in minerals rather than words. These ancient signs tell us that even as our ancestors struggled to find food, shelter, and community, they were also navigating a world full of unseen dangers.

From fossilized teeth to living brain cells

To understand how this ancient exposure affected brain development, we worked with geneticists and neuroscientists, and used stem cells to grow miniature versions of human brain tissue, called brain organoids. These small collections of cells have many characteristics of developing human brain tissue.

We gave some of these organoids a modern human version of a gene called nova1, and others an ancient, extinct version of the gene carried by Neanderthals and Denisovans. Nova1 is a gene that orchestrates early neurodevelopment. It also initiates brain cell responses to lead pollutants.

Next, we exposed both sets of organoids to very small, realistic amounts of lead—something that ancient humans would have encountered naturally.

The difference was amazing. Organoids with primitive genes showed clear signs of stress. Neural connections are not made as efficiently, and key pathways involved in communication and social behavior are disrupted. However, modern gene organoids were far more flexible.

It seems that somewhere along the evolutionary path, our species has developed better built-in protection against the harmful effects of lead.

A story of struggle

The environment — complete with lead exposure — evolved to accommodate modern human populations. Individuals with genetic variations that help them resist a threat are more likely to survive and pass those traits on to future generations.

Thus, lead exposure may be one of the many unseen forces that shaped the human story. By supporting the genes that make our brains stronger against environmental stressors, it can shape the way our neural networks develop, affecting everything from cognition to the rudiments of speech and social communication.

This does not change the fact that lead is a toxic chemical. It is one of the most harmful substances in our brains.

But evolution often works through struggle—even negative experiences can leave lasting, sometimes beneficial imprints on our species.

New context for a modern problem

Understanding our long relationship with lead gives new context to a very modern problem. Despite decades of bans and regulations, lead poisoning remains a global health problem. A recent UNICEF estimate shows that 1 in 3 children worldwide still have blood lead levels high enough to cause harm.

Our findings suggest that human organisms have evolved in a world full of chemical challenges. What has changed is not the presence of toxins, but the intensity of our exposure.

When we look at the past through the lens of science, we don’t just uncover old bones, we uncover ourselves.

In the industrial age, we have greatly expanded what used to be brief and infrequent natural exposures. From how our ancestors’ bodies and genes responded to environmental stressors, we can learn how to build a healthier, more resilient future.

This article is reprinted from The Conversation under a Creative Commons license. Read the original article.