Ancient lead exposure may have influenced how our brains evolved

Prehistoric hominids have been exposed to poisonous lead for at least 2 million years, a study of fossil teeth suggests, and modern humans may have evolved to cope with the toxic metal better than our ancient relatives.

Lead poisoning has long been thought to be a uniquely modern problem tied to industrialisation, poor mining practices and its use as an additive in fuel, which has been phased out since the 1980s.

It is particularly dangerous for children, impacting their physical and mental development, but it can also cause a range of severe physical and psychological symptoms in adults.

Renaud Joannes-Boyau at Southern Cross University in Lismore, Australia, and his colleagues wanted to find out whether our ancient relatives were also exposed to lead.

They analysed 51 fossil teeth from hominids including Australopithecus africanus, Paranthropus robustus, Gigantopithecus blacki, Homo neanderthalensis and Homo sapiens. The fossils were from Australia, South-East Asia, China, South Africa and France.

The scientists searched for lead signals in the teeth using laser ablation, which revealed bands of lead taken up by the teeth during periods of exposure when the hominids were still growing. This exposure could have come from environmental sources such as contaminated water, soil or volcanic activity.

Joannes-Boyau says the team was particularly struck by the amount of lead in the teeth of Gigantopithecus blacki, an ancient giant relative of today’s orangutans that lived in what is now China. “If it was a modern human that had this amount of lead in their body, then I would say this person was facing high exposure from industry or anthropogenic activities,” he says.

Next, the team investigated if there was any difference between the way modern humans coped with lead compared with Neanderthals. Using lab-grown models of the brain, called organoids, they studied both the Neanderthal and human versions of a gene called NOVA1 and tested the neurotoxicity of lead to the organoids.

“What we see is modern NOVA1 is much less stressed by the neurotoxicity of lead,” says Joannes-Boyau.

Most importantly, when organoids with archaic NOVA1 were exposed to lead, another gene called FOXP2 was severely disrupted.

“These genes are linked to cognition; they’re linked to language and linked to social cohesion,” says Joannes-Boyau. “And it is less neurotoxic for modern humans than it is for Neanderthals, which would have given a very big advantage to Homo sapiens and implies lead has played a role in our evolutionary journey.”

But Tanya Smith from Griffith University in Brisbane, Australia, isn’t convinced about the extent of lead exposure or whether work on organoids can be extrapolated to an evolutionary advantage for modern humans.

“This is a really complex paper that makes some highly speculative claims,” says Smith. “While it is no surprise to me that wild primates and ancient hominins were exposed to lead naturally, as we’ve published in multiple papers over the last seven years, the limited distribution, number and type of fossils included simply does not demonstrate that human ancestors were consistently exposed to lead over 2 million years.”

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