Two teeth from Neanderthal children who lived 250,000 years ago in what is today France contain evidence of repeated exposure to high levels of lead, a metal known to have adverse effects on the development of the brain and nervous system, according to new research led by Griffith University scientists.

“During fetal and childhood development, a new tooth layer is formed every day,” said Griffith University researcher Dr. Tanya Smith and her colleagues from Australia, France and the United States.

“As each of these ‘growth rings’ forms, some of the many chemicals circulating in the body are captured in each layer, which provides a chronological record of exposure.”

The scientists measured barium, lead and oxygen in two 250,000-year-old Neanderthal teeth for evidence of nursing, weaning, chemical exposure, and climate variations.

Elemental analysis of the teeth revealed short-term exposure to lead during cooler seasons, possibly from ingestion of contaminated food or water, or inhalation from fires containing lead.

“The two Neanderthal children either ingested or inhaled lead, representing the oldest documented lead exposure in any hominins,” the study authors explained.

“This occurred multiple times during the cooler seasons, potentially happening in caves as underground lead sources have been found within 15.5 miles (25 km) of the archaeological site.”

“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-author Dr. Christine Austin, a researcher in the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai.

In the study, the scientists used the sensitive high-resolution ion microprobe (SHRIMP SI) instrument to sample tooth layers and reconstruct the past exposures along incremental markings.

This evidence allowed the team 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.

The findings are consistent with mammals’ pattern of bearing offspring during periods of increased food availability.

The nursing duration of 2.5 years in one individual is similar to the average age of weaning in preindustrial human populations.

“Using SHRIMP SI enabled us to reveal that one Neanderthal was born in spring and weaned in the autumn 2.5 years later, and that both Neanderthal children were more likely to be sick during colder periods,” Dr. Smith said.

“At the time they grew up, 250,000 years ago, this region of southeast France was much cooler and more seasonal than it is today.”

The team now plans to find out what the Neanderthals did in the depths of winter that resulted in exposing their children to high levels of toxic lead.

“This will give fresh insight into Neanderthal behavior. Another step will be to push further back in time and study the teeth of hominins and early humans in the birthplace of the human species — Africa,” Dr. Smith said.

The study is published in the journal Science Advances.

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Tanya M. Smith et al. 2018. Wintertime stress, nursing, and lead exposure in Neanderthal children. Science Advances 4 (10); doi: 10.1126/sciadv.aau9483