Humans and our ancestors have been exposed to lead for up to two million years, researchers have discovered, overturning the idea that lead poisoning is a relatively modern phenomenon.
Additionally, widespread exposure to toxic metals may have influenced the evolution of our species’ ability to communicate. This would have given Homo sapiens an important advantage over our Neanderthal cousins, who are more susceptible to lead toxicity, the study suggests.
“Evolution often proceeds through adversity. Stressors such as drought, lack of food and water, and toxins not only threaten survival, but can also drive selection for traits that make species more adaptable,” said study co-author Renaud Joannes-Boyau, professor at Southern Cross University in Australia and director of the Geoarcheology and Archeology Research Group (GARG). “Lead exposure may be one such hidden force in our evolutionary history,” he told Live Science via email.
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But experts say the study has limitations, as it estimates lead exposure by measuring lead levels in the teeth of many humans and related species.
“It’s not clear whether the amounts of lead found in ancient teeth were sufficient to actually affect health,” said John Hawkes, an anthropologist at the University of Wisconsin-Madison who was not involved in the study. “Measuring chemicals in tooth enamel has become incredibly sensitive. It’s possible that we’re detecting levels so small that they don’t make a difference,” he told Live Science via email.
According to the Cleveland Clinic, lead is toxic and high levels of the metal in the body can cause multiple health problems, especially in children. It can damage the nervous system, especially the brain and other organs, and cause severe learning and behavioral problems.
According to the Environmental Protection Agency, most lead poisonings currently result from human activities and products such as paint, mining, and smelting.
But lead also occurs in nature and can be found “in varying concentrations throughout the Earth’s crust and in virtually all rocks, soils, sediments, and waterways,” the researchers wrote in a study published Oct. 15 in the journal Science Advances.
“Animals, including humans, can be exposed to significant levels of lead by drinking contaminated water, consuming contaminated food, and breathing contaminated air (such as smoke from fires or sandstorms),” the researchers added.
contaminated teeth
In the new study, researchers examined 51 fossilized teeth between 1.8 million and 100,000 years old from a variety of species, including Homo sapiens’ closest relative Neanderthal, close relatives such as Australopithecus africanus and Paranthropus robustus, and the extinct great ape Gigantopithecus black.
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“Teeth form gradually during childhood, so they preserve a detailed record of early childhood exposures, when the brain is most vulnerable,” said Joannes-Boyau.
Analysis revealed that 73% of the samples showed “clear signs of temporary lead exposure,” the study said. This shows that lead exposure is not a modern phenomenon, but has been affecting our ancestors and relatives for millions of years.
Exposure levels vary, some lower than modern industrial levels, others higher, but are generally enough to affect young, developing brains, Joannes-Boyau noted.
growing mini brain
To investigate how lead exposure affected the development of Homo sapiens, researchers created two different versions of brain “organoids,” miniaturized models of the full-size human brain.
Each organoid version contained a different variant of the gene NOVA1. Modern humans have a unique version of this gene, which is important for brain development and is also associated with language ability. Neanderthals and other human relatives have slightly different versions of this gene.
When exposed to lead, organoids with the modern NOVA1 gene showed greater resistance to the toxic metal than organoids with the ancient variant. In particular, the Homo sapiens version of NOVA1 appears to help maintain the activity of a gene called FOXP2, which plays an important role in the development of human speech and language.
“When the brain is exposed to stressors such as lead, the latest NOVA1 variants maintain stable FOXP2 function and help protect pathways related to language, communication and cognition,” said Joannes-Boyau.
In contrast, in brain organoids with archaic NOVA1 mutants, FOXP2 expression was altered upon exposure to lead.
This may have given humans an evolutionary advantage, said study co-author Alison Muotri, director of the Sanford Center for Stem Cell Education and Integrative Space Stem Cell Trajectory Research at the University of California, San Diego.
“Presumably, the modern variant NOVA1 emerged after lead exposure, but was rapidly selected because it had an advantage over other hominins such as Neanderthals,” he told Live Science via email. “This is another example of evolution in action.”
But the data on the NOVA1 gene are open to interpretation, Debbie Guatelli-Steinberg, a professor in the Department of Anthropology at The Ohio State University, told Live Science in an email.
“The authors argue that the human NOVA1 variant gave humans a competitive advantage over other hominins, including Neanderthals,” said Guatelli-Steinberg. “This idea is speculation.”
Hawks said the study raises questions about how these ancient human ancestors and relatives were exposed to lead. “Did they pick up lead when they used the sparkly minerals as pigments?” Hawks said. “Did they pick it up from pollutants through combustion? Or did they pick it up from the plant foods they ate? These are open questions. We’d love to know the answers.”
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