Exposure to lead in the past may have influenced the evolution of our brains

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

Lead poisoning has long been considered a modern problem, linked to industrialization, poor mining practices and its use as a fuel additive, which has been phased out since the 1980s.

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

Renaud Joannes-Boyau of Southern Cross University in Lismore, Australia, and colleagues wanted to know if our ancient relatives were also exposed to lead.

They analyzed 51 fossil hominid teeth, including African Australopithecus, A robust paranthropist, Gigantopithecus blacki, Homo neanderthalensis And A wise man. The fossils came from Australia, Southeast Asia, China, South Africa and France.

The scientists looked for lead signals in the teeth using laser ablation, which revealed bands of lead absorbed by the teeth during periods of exposure while the hominids were still growing. This exposure could 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 Black Gigantopithecusan ancient giant relative of today’s orangutans that lived in what is now China. “If it was a modern human who had this amount of lead in their body, then I would say that this person was facing high exposure from industrial or anthropogenic activities,” he says.

Next, the team studied whether there was a difference between how modern humans handled lead and how Neanderthals handled it. Using lab-grown brain models called organoids, they studied the Neanderthal and human versions of a gene called NEW1 and tested lead neurotoxicity on organoids.

“What we see is modern NEW1 is much less stressed by lead neurotoxicity,” explains Joannes-Boyau.

More importantly, when organoids with archaic NEW1 were exposed to lead, another gene called FOXP2 was greatly disrupted.

“These genes are linked to cognition, language and social cohesion,” explains Joannes-Boyau. “And it is less neurotoxic to modern humans than to Neanderthals, which would have given a very big advantage to A wise man and implies that lead played a role in our evolutionary journey.

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

“This is a very complex article that makes highly speculative claims,” says Smith. “While it does not surprise me that wild primates and ancient hominids were naturally exposed to lead, as we have published in several papers over the past seven years, the limited distribution, number and type of fossils included simply do not demonstrate that human ancestors were systematically exposed to lead for more than 2 million years.”

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