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Fossilized dental crowns contain a lot of information about past climates and life events. Credit: Tanya M Smith, Author Provided
Increasing variation in climate has been implicated as a possible factor in the evolution of our species (Homo sapiens) 300 000 years ago, as well as the more recent disappearance of our enigmatic evolutive cousins, the Neanderthals.
But knowing the impact of this change from year to year has always been a challenge.
Most prehistoric climate models are derived from large-scale data such as deep-sea cores or layers of terrestrial sediments. These methods provide information on a scale of thousands of years, making it impossible to understand the direct impact of seasonal weather patterns on ancient humans and their evolutionary parents.
My colleagues and I have found a solution using clues from our own mouth, as we detail it today in an article in Science Advances. We used teeth to reveal climatic data recorded during the development of old hominines.
In the teeth
Teeth are a very useful indicator of past environments.
This is possible because the teeth have biological rhythms and key events block them. These faithful internal clocks operate night and day, year after year, and include daily growth lines and a marked line at birth.
Histologists like me have carefully seen teeth, removed tiny slices, and carefully mapped microscopic growth records during childhood.
For this new study, we examined the enamel in the fossilized teeth of two Neanderthal children (dated from 250,000 years ago) and a modern human child (dated from there). 5,000 years ago) of an archaeological site in southeastern France called Payre.
Using the high resolution ionic sensitive microprobe (SHRIMP) from the Australian National University, we measured the weekly change in oxygen isotope ratio in these old teeth.
Our approach is based on the fact that two atomic variants of natural oxygen exist with predictable variations.
During prolonged periods of warm weather, the surface water is higher in the heavy variant of oxygen. The opposite pattern occurs during cold periods.
When individuals drink in streams or puddles of water, values from these sources are recorded in the hard mineral component of the teeth being formed.
SHRIMP measurements allowed us to create multi-year paleoenvironmental records from fossil teeth.
A 250,000-year-old Neanderthal tooth is an unprecedented record of birth seasons (age 0), breastfeeding (yellow box), disease (red line) and exposure to lead (blue lines) in the first 2.8 years of this child's life. Oxygen isotope values sampled on a weekly basis are presented as a ratio of heavy to light variants.
What the teeth reveal
Oxygen records show that both Neanderthals lived in cooler and more seasonal periods than the modern man who grew up in the same place more recently.
This is consistent with our basic understanding of ancient climates in France, since 250,000 years ago this region was cooler than the past 10,000 years, when the modern, unlucky human child lived and died.
We have already shown that teeth maintain accurate records of milk intake during breastfeeding, proving that orangutan mothers are champions of lactation – they breastfeed their children for eight years or more .
In this study, we were able to associate seasonal cycles during tooth formation with breastfeeding behavior, showing that a Neanderthal child was born in the spring and had stopped consuming his mother's milk. two and a half years later, in the fall.
Even more surprising is the fact that both Neanderthals have been exposed to lead at least twice during the colder periods of the year, probably through the consumption of food and / or d & # 39; contaminated water.
Lead is naturally present in several historic mines in this region of France. This is the oldest known prehistoric exposure to this neurotoxic substance. No level is considered safe for humans or animals, and these exhibits took place during a critical period of the early years of life of these Neanderthals.
First molar tooth of a 250,000 year old Neanderthal child. The dotted yellow lines indicate the beginning and end of breastfeeding, a red dashed line corresponds to a disease and blue dashed lines indicate lead exposures. Credit: Tanya Smith and Daniel Green
More teeth needed
These findings raise intriguing questions about the behavior of Neanderthals who require further study, and young children with unworn teeth are particularly useful. Although dozens of young Neanderthals have been discovered, it is very difficult to convince conservators of the collections to conduct this type of semi-destructive study.
But the more thoroughly we examine teeth, the more information we collect from years to years about the lives of ancient peoples.
Our approach will also facilitate the necessary tests of theories on the impact of climate change on human technological development, as well as the understanding of nursing behavior of Neanderthal, a determinant of population growth and life.
Previously, my colleagues and I had discovered that an eight year old Belgian Neanderthal had been weaned at the age of 1.2 years. This was probably atypical because the breastfeeding signal was rapidly decreasing and the individual was experiencing stress on his first molar at this point in time.
We do not know if that means that he was separated from his mother or just really sick – but it is likely that Neanderthal children were looked after longer when they could.
Our new approach allows scientists to flesh out the lives of older children with unprecedented details, including detailed views of life in Ice Age Europe, through the remarkable stories that their teeth tell.
Explore further:
Researchers discover the oldest lead exposure recorded on 250,000 year old Neanderthal teeth
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