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The Neanderthals were close cousins of humans who went extinct approximately 40,000 years ago, during the last ice age. Many questions remain about their lives and how they coped with the extreme environments and glacial periods of Eurasia. Now, by analyzing the teeth of two Neanderthal children from southern France, scientists have discovered new information about what the climate and aspects of Neanderthal life were like 250,000 years ago.

Daniel Green, a postdoctoral fellow in mineralized tissue biology at the Forsyth Institute, was part of an international research team that published its findings recently in the journal Science Advances. Using new methods of chemical analysis, the researchers found that the two Neanderthal children whose teeth they examined lived in a highly seasonal environment with intense winters and summers. Scientists were able to determine that the children weaned off mother’s milk around age two and a half years of age, and that they were exposed to lead at specific moments in their lives.

The chemical archive of teeth
Much like the rings that form each year as a tree grows, teeth grow in increments as well. But instead of forming annually, a new increment appears each day when teeth form in the mouths of children. These increments can reveal information about the chemicals in a child’s body—and in their environment—at any given point in time.

“These increments form in chemical equilibrium with our body chemistry, and our body chemistry is in equilibrium with our environment—what we drink, what we eat, and what we breath,” Green said.

For the study, researchers developed a technique to map out, in teeth, the variants of oxygen atoms called isotopes. The quantities of isotopes in teeth change with the outside temperature and environment. The scientists’ analysis revealed that the two Neanderthal children were born in springtime, and that they lived through winter and summer seasons that were more extreme than what we know modern humans from the same location experienced 5,000 years ago. Green said this method could be used to build a detailed record of seasonal climate patterns in the past and could help scientists better predict climate changes in the future.

Researchers also measured barium concentrations from the children’s teeth. This allowed them to estimate the age at which the Neanderthal children were weaned off their mother’s milk—around two and a half years after they were born.

“That was really interesting for us to know,” Green said, adding that researchers have long been curious about the ways in which modern humans are different, or not so different, from Neanderthals.

“We characterize humans as having a very unique period of childhood with a lot of investment of parental care. From what we see in their teeth, Neanderthals look like they weaned their children in a way quite similar to humans,” Green said. Weaning off mother’s milk at age two and a half or three is typical of humans today living in non-industrialized societies, Green explained.

Mysterious lead exposure
Green said that his colleagues Tanya Smith at Griffith University, who led the project, and Christine Austin and Manish Arora at Mount Sinai Hospital, also used the teeth to map lead exposure. They found that the Neanderthal children were exposed to lead at discrete moments in their lives, specifically in mid and late winter.

“This suggests that the children were eating or drinking contaminated water, or possibly visiting caves that contained natural lead deposits,” said Smith, Associate Professor in the Australian Research Centre for Human Evolution at Griffith University

The presence of lead is surprising, Green said, because the children lived long before manufacturing activities liberated large amounts of lead into the air and water. There should have been very low levels of lead in the environment at that time, Green explained.

Scientists can’t definitively explain where the lead came from, but they have a hypothesis.

“Since Roman times, humans have exploited lead deposits in that area of Southern France,” Green said. “It’s possible there was a groundwater source that was contaminated that the Neanderthals drank from. Perhaps it was in the water because it came from rocks under the ground.”

Now that Green and his colleagues have published this study and validated that their analysis technique works, they can use the method to analyze other specimens, both new and old. This could allow us to reconstruct the climate further back in time than ever before.

“By getting this kind of detail from the past, we can have a much better sense of baselines for what we expect moving forward,” Green said. “With its expertise in dental development and childhood health, I think the Forsyth will continue to play an important role in this kind of transformative research.”