Pity the poor Neanderthal mother: She had to nurse her children through colder winters and more illnesses than the mothers of most prehistoric modern humans in Europe, according to a new study of the teeth of two Neanderthal kids who lived 250,000 years ago in France. And both Neanderthal toddlers suffered from repeated lead exposure—the earliest known evidence of lead poisoning in members of the human family. The study offers a startlingly intimate view of the lives of ancient children.

Tanya Smith taps into the record of growth, climate, and diet preserved in the enamel of a Neanderthal child who lived 250,000 years ago. TANYA SMITH AND GRIFFITH UNIVERSITY

The study is “mind blowing” because it gives such a detailed record of how harsh winters, the water supply, and nursing duration can influence growth in early childhood, says paleoanthropologist Leslea Hlusko of the University of California, Berkeley, who was not part of the team. The researchers “provide powerful insight into some of the most intimate moments of life—the relationship between the Neanderthal as a baby and its mama.”

Researchers have long known that Neanderthals, with their barrel chests and robust limbs, were well-adapted for survival in the frigid temperatures of Europe, where their fossils date back more than 400,000 years. But it’s been difficult to tie climate events to individual Neanderthals’ lives or even to specific fossil sites.

Now, researchers have shown the direct effects of climate on the lives of two young children (who lived until they were teens or young adults) from Payre, an archaeological site in the Rhone Valley of southeast France, and a modern human child who lived at the same site 5400 years ago.

Biological anthropologist Tanya Smith of Griffith University in Brisbane, Australia, prepared thin sections of the teeth of two Neanderthal children and one modern human child. With a polarized light microscope, she painstakingly traced the daily growth lines that are recorded in the enamel, much like tree rings. Her international colleagues also measured oxygen isotopes, barium, and lead in the teeth.

By timing the surges of barium, a marker of milk consumption in the teeth, they found that both Neanderthals nursed for 2.5 years before they were weaned. That’s just about the length of time that modern humans in hunter-gatherer societies nurse their babies, Smith says. It also suggests the weaning time of another Neanderthal, which Smith had previously traced to 15 months, was not the norm, she says.

The ratio of different isotopes of oxygen in the children’s teeth suggests the Neanderthal children endured cooler winters and more extreme seasonal variation in climate than did the more recent modern human from the same site, a finding that fits other evidence of a more stable climate during the past 10,000 years. Both Neanderthals also had more stress lines—signals of disruption in enamel growth—during winter, suggesting they were sicker in that season. These disruptions were less frequent in the modern human child.

Both Neanderthals were also exposed to lead at least twice. This represents the oldest documented exposure to lead in hominin remains, the researchers report today in Science Advances. Two lead mines lie only 25 kilometers from the site, and the children may have ingested lead-rich food or water—or inhaled lead from smoky fires.

The evidence that Neanderthals nursed their young until they were 2.5 years through sickness and cold spells suggests Neanderthal moms took care of their young as intensively as modern mothers do. Now, researchers are eager to try these methods of studying growth in other types of humans. “These techniques help us build more nuanced pictures of what their lives were like season to season,” says biological anthropologist Katie Hinde of Arizona State University in Tempe. “This gives us insight into the origins of health and disease and let us understand more about the environments that shape humans and our close relatives.”