Traces of lead found in the molars of two young Neandertals found in southeast France provide the earliest recorded evidence of lead exposure in hominids.
Like tiny time capsules, chemical signatures in the 250,000-year-old chompers chronicle specific times — mostly during the winter months — when the two individuals were exposed to the element as children, researchers report online October 31 in Science Advances.
“There are clocks inside our mouths,” says Tanya Smith, a human evolutionary biologist at Griffith University in Brisbane, Australia. By analyzing fossilized teeth, “you get this incredible insight into what [life] was like in the past.” The finding was part of a study that tracked nursing habits of the species and seasonal changes in the environment.
Tooth enamel grows in layers, trapping chemicals contained in the water and food that animals, including humans, consume. Neandertal teeth were no different in this regard. Both tooth samples revealed layers with elevated lead levels at multiple points throughout the youngsters’ first years of life. Chemical analysis of thin slices of tooth from one Neandertal, for instance, revealed the first signs of lead exposure starting at about 2.5 months of age, increasing at 9 months and spiking just after turning 2 years old.
Code leadA chemical analysis conducted on two Neandertal teeth revealed elevated traces of lead.
In this specimen, reds, yellows and greens indicate higher levels of lead in the enamel layers. Cooler blue tones denote lower levels of the element.
Because teeth grow in layers that can be chronicled over time, the team was able to pinpoint when in the individual’s life these lead exposures occurred.
The team is still searching for the source of the exposure. One possibility: Present-day lead mines just 25 kilometers from where scientists found the fossilized teeth. Smith and her colleagues suspect that as children, the Neandertals either inhaled lead or ingested it in food they foraged.
“That’s a normal ranging distance for a Neandertal,” Smith says. “It’s not hard to believe that they may have encountered deposits or consumed food that was contaminated.”