A study of fossil teeth reveals that prehistoric hominids were exposed to lead for at least 2 million years, potentially influencing brain evolution. Modern humans appear to have adapted better to the toxin than relatives like Neanderthals, according to research using ancient samples and brain organoids. However, some experts question the extent of this exposure and its evolutionary implications.
Lead poisoning, long considered a modern issue linked to industrialization and phased out since the 1980s, may have afflicted ancient hominids for millions of years. Researchers led by Renaud Joannes-Boyau at Southern Cross University in Lismore, Australia, analyzed 51 fossil teeth from species including Australopithecus africanus, Paranthropus robustus, Gigantopithecus blacki, Homo neanderthalensis, and Homo sapiens. These fossils originated from sites in Australia, South-East Asia, China, South Africa, and France.
Using laser ablation, the team detected lead bands in the teeth, indicating exposure during growth periods from environmental sources like contaminated water, soil, or volcanic activity. Notably high lead levels appeared in Gigantopithecus blacki teeth from 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,” Joannes-Boyau said.
To explore evolutionary differences, the researchers created brain organoids modeling Neanderthal and modern human versions of the NOVA1 gene and tested lead's neurotoxicity. “What we see is modern NOVA1 is much less stressed by the neurotoxicity of lead,” Joannes-Boyau noted. Exposure disrupted the FOXP2 gene in archaic versions, which is linked to cognition, language, and social cohesion. “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,” he added.
Lead is especially harmful to children, affecting physical and mental development, and causes severe symptoms in adults. Yet Tanya Smith from Griffith University in Brisbane, Australia, critiques the findings. “This is a really complex paper that makes some highly speculative claims,” she said. Smith argues that the limited number and distribution of fossils do not prove consistent exposure over 2 million years, though natural lead in wild primates and ancient hominins is unsurprising based on prior studies.
The research was published in Science Advances (DOI: 10.1126/sciadv.adr1524).