Manish Arora, PhD, MPH; and Christine Austin, PhD
Neanderthals became extinct more than 20,000 years ago, but an innovative study of teeth by an international team, including researchers at the Icahn School of Medicine at Mount Sinai, has uncovered details about their lives that may lead to new insights into human evolution and into chemical exposures that affect health outcomes now.
The study is the first to use teeth to explore in weekly increments the relationship between ancient climate change and the development of hominins—humans and their immediate ancestors. Researchers examined remains recovered from Payre, an archaeological site in the Rhone Valley of Southeastern France, analyzing one tooth each from two Neanderthal children who lived 250,000 years ago, and another tooth from a “modern” human child who lived 5,000 years ago.
“Much like trees, teeth have growth rings that enable us to look at what happened in the life of an individual on a weekly basis,” says co-author Christine Austin, PhD, Assistant Professor of Environmental Medicine and Public Health, Icahn School of Medicine. “For these teeth, we cut a sample approximately 100 microns thick, or the width of a human hair, removed a small amount of material from the surface of the growth rings using a laser, analyzed the elements in that material using inductively coupled plasma mass spectrometry, and then constructed a timeline of exposure to the elements for each individual.”
Analyzing a slice of a Neanderthal child’s tooth, 100 microns thick, provided a timeline of development and chemical exposures. For example, a “stress line” around day 707 of the child’s life indicated a period of severe illness or hunger.
This technology was developed by Manish Arora, PhD, MPH, the Edith J. Baerwald Professor of Environmental Medicine and Public Health, Icahn School of Medicine, and senior author of the study, which was published in Science Advances in October 2018. “Dr. Austin’s work is a game changer for the way we analyze archaeological samples and for our understanding of how environmental stressors have impacted the evolution of modern humans and how they continue to impact our health,” Dr. Arora says. “Her work on the evolution of breastfeeding has direct relevance to understanding the benefits of breast milk in modern medical practice.”
Dr. Austin and her colleagues at institutions in France and Australia noted developmental deformations in the Neanderthal teeth that reflected the stresses of life during harshly cold winters. In addition, both Neanderthals were exposed to lead at least twice during late winter or early spring. Dr. Austin says two mines are located within foraging distance of the recovery site, indicating that food and water from the area may have been contaminated with lead. There were also signs of high, acute exposure, which could have resulted from an event such as inhalation of a cave fire.
“Previously, we thought that lead exposure mainly happened post-industrialization,” Dr. Austin says. “Now we see that is not the case, and that raises questions about the impact of this neurotoxin on their neurodevelopment and ultimately their behavior. That is something we want to explore further.”
Equally of interest were the findings related to breastfeeding. One of the Neanderthals was weaned at about two and a half years of age, which is similar to the norm for early humans. “Compared to other primates, humans wean early, which enables higher reproductive rates and is likely one of the reasons for our species’ success,” Dr. Austin says. “Seeing a human-like weaning pattern in Neanderthals is very interesting and raises questions about when this nursing behavior evolved.”
Dr. Austin says the study could also lead to insights into chemical exposures from breast milk that could impact lifelong health. “There is a growing body of data on the importance of breast milk in the development of an infant’s microbiome,” she says. “By better understanding how the composition of breast milk has evolved, in addition to breastfeeding practices, we can start to propose interventions at critical developmental windows that mitigate exposure to environmental stresses and toxins and thus improve health outcomes.”