Ancient lead exposure may have influenced how our brains evolved

Evidence from fossilized teeth indicates that our prehistoric ancestors encountered harmful lead for over 2 million years, and today’s humans might have developed a better resistance to this toxic element compared to their ancient relatives.

Historically, lead poisoning has been regarded as a modern dilemma, closely related to industrialization, inadequate mining techniques, and its usage as a fuel additive, which has been largely eliminated since the 1980s.

Children are particularly susceptible to lead’s adverse effects, affecting both their physical and mental growth, but adults can also experience various severe physical and psychological issues.

Renaud Joannes-Boyau from Southern Cross University in Lismore, Australia, and his team investigated whether our ancient ancestors faced similar lead exposures.

The researchers analyzed 51 fossilized teeth from various hominids, including Australopithecus africanus, Paranthropus robustus, Gigantopithecus blacki, Homo neanderthalensis, and Homo sapiens. The fossils originated from locations in Australia, Southeast Asia, China, South Africa, and France.

The team utilized laser ablation to detect lead uptake in the teeth, revealing periods of exposure while the hominids were still growing. This exposure likely stemmed from environmental sources like contaminated water, soil, or volcanic activity.

Joannes-Boyau noted the surprisingly high levels of lead found in the teeth of Gigantopithecus blacki, an ancient giant related to modern orangutans that roamed what is now China. He commented, “If a contemporary human exhibited this level of lead exposure, I’d assert they faced significant exposure from industrial or human activities.”

The researchers further explored whether modern humans process lead differently than Neanderthals. They examined lab-grown brain organoids to compare the Neanderthal version of the gene NOVA1 with that of modern humans and assessed how lead affected neurotoxicity in these organoids.

Joannes-Boyau highlighted their findings: “Modern NOVA1 shows significantly less stress in the presence of lead neurotoxicity.”

Critically, when archaic NOVA1 organoids were exposed to lead, the function of another gene, FOXP2, was severely affected.

“Both these genes relate to cognitive function, language capabilities, and social cohesion,” Joannes-Boyau explained. “The neurotoxic effect of lead appears to be less detrimental for modern humans than for Neanderthals, suggesting an evolutionary advantage for Homo sapiens and indicating that lead may have impacted our evolutionary development.”

Nonetheless, Tanya Smith from Griffith University in Brisbane, Australia, casts doubt on the significance of lead exposure and the applicability of their organoid findings to modern humans’ evolutionary advantages.

“This complex study makes several speculative assertions,” remarked Smith. “While it’s unsurprising that ancient hominins had natural lead exposure, as shown in numerous studies over the past seven years, the limited sample size and variation in the fossils analyzed do not substantiate that human ancestors experienced consistent lead exposure over a span of 2 million years.”