Where did Ötzi live? Delta asked the toothfairy

Where did Alpine Iceman Ötzi live? Data about tooth enamel, collected by Esther Plomp, could help answer this question and shed light on many more archaeological findings.

Istope analysis could shed more light on this man's life. (Photo: Science)

Anthropologists and archaeologists are thrilled, witness the praise on Twitter. ‘Exactly the type of isotope work the field needs more of!’, writes Erin Wessling from Cambridge University. ‘Great paper by @PhDToothFAIRy et al. looking at variation within individuals for C, O, and Sr #isotopes’, tweets bioarchaeologist Chris Stantis from Bournemouth, England.

What is all the excitement about? Researcher Esther Plomp, aka PhDToothFAIRy, and several of her colleagues at the VU University in Amsterdam have refined a method called isotope analysis, which is widely used by scientists to research human and animal diets in the past, to assess where our ancestors lived and map out migration routes. They wrote about their findings last month in the American Journal of Physical Anthropology. Plomp, who works as a data steward at TU Delft, is the first author.

Reading the bones and enamel of teeth

Isotope analysis in short is the identification of isotopic signatures. Strontium isotopic analysis for instance can tell researchers where an individual grew up, as the isotopic signature of an individual’s tooth is formed during childhood. Plants have varying amounts of different strontium isotopes depending on the bedrock of the area they are grown in, and this can be read in the bones and enamel of the teeth of the humans who feed on them. Finding a certain signature, consisting of a very subtle increase or decrease of one of the isotopes, can tell a lot about someone’s life events.

Based on such analysis, for instance, an article in Science in 2003 postulated that Alpine Iceman Ötzi migrated during his life (5,200 years ago), from the area south of the discovery site to the northwest or other areas with higher altitudes than the discovery site. Ötzi was a well-preserved human mummy, who was recovered from a glacier in the main Alpine watershed between Italy and Austria in 1991. A lot of scientific debate has been going on about his life since, about who he was and where he came from.

According to Plomp, the conclusion in the Science paper in 2003 is debatable. Ötzi might just as well have lived north of the Alpine watershed in an area called the Otztal, as was postulated prior to the 2003 publication.

Wisdom teeth

The problem with the technique of isotope analysis when it comes to the teeth, was that thus far no study had systematically examined within person variation in strontium, oxygen, and carbon isotopes in human enamel, the hard outer layer of the tooth. That omission affects interpretations. Plomp and her colleagues performed the first systematic study to map the variation that every person has in their dentition, by studying the composition of sets of wisdom teeth of dozens of individuals from the Netherlands, Iceland, the United States, the Caribbean, Colombia, Somalia, and South Africa.

“We found quite high levels of variation among people: up to 1.4 promille difference within a tooth,” says Plomp. Though that may not seem like a lot, that amount of difference is usually regarded as sufficient to identify a change in the individual’s diet or location. “But the individuals that we analysed did not change their diet or location when their wisdom teeth were formed. We show that one should be more careful when it comes to drawing conclusions about small changes in these isotopic signatures, since the amount of noise – the amount of within-person variation – can be very high.”

That goes for the conclusion drawn on the life of Ötzi. Ötzi may have moved around, but we cannot conclude that he migrated between different areas based on the minor changes in his enamel. Instead, he might just as well have lived his entire life in the area south of the discovery site.”

Another example of possible overestimation of migration can be found in a 2017 article in the Journal of Archaeological Science, where the provenance of a group of slaves whose remains were found in a cemetry in Cape Town was assessed. Some of these individuals clearly travelled large distances, likely thousands of kilometers, as they show very different isotopic signatures which are normally found in Mozambique. Based on Plomp’s findings, however, some of the individuals that were previously thought to have migrated, may instead have spent their life in or around Cape Town, as only minor differences are visibile in their isotopic signatures.

The data Plomp collected, which could shed light on many archaeological findings, are stored in the 4TU data repository.

Redacteur Tomas van Dijk

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