Using evidence found in teeth from two Neanderthals from southeastern France, researchers from the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai report the earliest evidence of lead exposure in an extinct human-like species from 250,000 years ago.
The international, multi-institute study is the first to report lead exposure in Neanderthals and is the first to use teeth to reconstruct climate during and timing of key developmental events including weaning and nursing duration, which are key determinants of population growth.
Including biological anthropologists, archaeologists, earth scientists, and environmental exposure experts, the researchers measured barium, lead, and oxygen in the teeth for evidence of nursing, weaning, chemical exposure, and climate variations across the growth rings in the teeth. Elemental analysis revealed short-term exposure to lead during cooler seasons, possibly from ingestion of contaminated food or water, or inhalation from fires containing lead.
During fetal and childhood development, a new tooth layer is formed every day. As each of these “growth rings” forms, chemicals circulating in the body are captured in each layer, providing a chronological record of exposure. The researchers used lasers to sample these layers and reconstruct past exposures along incremental markings, similar to using growth rings on a tree to determine its growth history.
The evidence allowed the researchers to relate the individuals’ development to ancient seasons, revealing that one Neanderthal was born in the spring and that both Neanderthal children were more likely to be sick during colder periods. These findings are consistent with mammals’ pattern of bearing offspring during periods of increased food availability.
The 2.5-year nursing duration in one individual is similar to the average age of weaning in preindustrial human populations. Yet the researchers note that they can’t make broad generalizations about Neanderthals due to the small study size. However, they say their methods offer a new approach to answering questions about long extinct species.
“Traditionally, people thought lead exposure occurred in populations only after industrialization, but these results show it happened prehistorically, before lead had been widely released into the environment,” said co-lead author Christine Austin, PhD, assistant professor in the Department of Environmental Medicine and Public Health.
“Our team plans to analyze more teeth from our ancestors and investigate how lead exposures may have affected their health and how that may relate to how our bodies respond to lead today,” Austin said.
“Dietary patterns in our early life have far reaching consequences for our health, and by understanding how breastfeeding evolved, we can help guide the current population on what is good breastfeeding practice,” said Manish Arora, PhD, BDS, MPH, professor and vice chairman of the Department of Environmental Medicine and Public Health.
“Our research team is working on applying these techniques in contemporary populations to study how breastfeeding alters health trajectories including those of neurodevelopment, cardiac health, and other high priority health outcomes,” Arora said.
“This study reports a major breakthrough in the reconstruction of ancient climates, a significant factor in human evolution, as temperature and precipitation cycles influenced the landscapes and food resources our ancestors relied on,” said lead author Tanya Smith, PhD, associate professor at Griffith University.
The study, “Wintertime Stress, Nursing, and Lead Exposure in Neanderthal Children,” was published by Science Advances.