Our hominid ancestors navigated a perilous world during the Pleistocene era, facing numerous challenges that included exposure to toxic elements such as lead. While contemporary discussions often associate lead poisoning with modern issues—like lead pipes used by the Romans or industrial pollution—a recent study indicates that lead exposure is a much older problem. In fact, evidence suggests that lead exposure predates the emergence of our genus, Homo, and has been a silent adversary for nearly two million years.
Paleoanthropologist Renaud Joannes-Boyau and his team from Australia’s Southern Cross University conducted a groundbreaking study, examining the teeth of 51 fossils, including both apes and hominins. Their findings revealed alarming levels of lead exposure in these ancient beings, particularly during their formative years. The tooth enamel, which develops in layers similar to tree rings, serves as a historical record of childhood health, including exposure to lead and other toxins.
In an astonishing 71% of the sampled hominin teeth, scientists identified distinct dark bands of lead in the enamel, indicating significant lead exposure during critical early development stages. This group included fossils from our own species, found in China and dating back 100,000 years, as well as French Neanderthals from 250,000 years ago. Additionally, fossils from ancient hominins, like Australopithecus africanus and Paranthropus robustus, dating back between one and two million years in South Africa, were also analyzed.
This study builds on previous research that indicated ancient hominins dealt with lead exposure in their environments. Notably, two Neanderthals from 250,000 years ago in France had already shown evidence of lead exposure, which was previously the oldest known case. The question arises: how were our ancestors exposed to lead long before industrial activities, such as silver smelting and plumbing, became common?
Research published in 2015 revealed that certain caves inhabited by Neanderthals in Spain contained enough heavy metals, including lead, to classify them as contaminated. Natural deposits of lead are found in various geological formations, making it possible for ancient hominins to encounter lead through their environments. Additionally, factors such as wildfires and volcanic eruptions could have released lead particles into the atmosphere, further exposing these early humans to toxic elements.
The analysis conducted by Joannes-Boyau and his colleagues highlighted significant differences in lead exposure among various hominin species. Through their study of fossils from the Cradle of Humankind in South Africa, they found that A. africanus exhibited the highest lead levels, while P. robustus showed signs of minimal exposure. These variances can be attributed to differences in diet and ecological niches, with more varied diets leading to higher lead accumulation through the food chain.
Intriguingly, the research team also explored the potential evolutionary implications of lead exposure on human development. They focused on the NOVA1 gene, which is known to influence brain development and response to lead. While some evidence suggests that this gene has evolved in modern humans compared to other primates, the exact implications of lead exposure on our evolution remain ambiguous.
The study conducted by Joannes-Boyau and his colleagues highlights the long-standing issue of lead exposure and its potential ramifications on our evolutionary history. As modern humans grapple with the consequences of lead pollution, it is essential to recognize that our ancestors faced similar challenges in their quest for survival. Understanding the impact of lead on ancient hominins not only sheds light on their health and development but also opens avenues for further research into the evolutionary adaptations that may have arisen in response to environmental toxins.
