To determine origin, researchers look at teeth, which mineralize in the first few years of childhood and remain unchanged through life. Bones re-mineralize constantly and their composition indicates the mineralization of the last ten to 20 years of life.
"The outcome also really depends on the local geologic/hydrological variation, which in the case of the Iceman was particularly well suited," said Müller.
Given the variation in rock, soil, and water type, the researchers were able to divide Ötzi's potential range into four distinct areas. For example, the researchers looked at a particular oxygen isotope to determine if the water Ötzi drank came from the Austrian or Italian side of the Ötzal Alps.
"This is possible," said Müller, "because the Alps form a watershed in the area, so rain and snow north and south of the Alps is isotopically different in oxygen."
The result pins the Iceman's place of origin to a few valleys on the south side of the Alps but suggests that he migrated to a different area during adulthood. The data are also consistent with the idea that he spent a few months each summer high up in the mountains.
Shepherd or Hunter
According to the composition of Ötzi's bones, he spent anywhere from a maximum of two months to about one month each year above the timber line.
Müller said the evidence is consistent with his theory that Ötzi was a shepherd, going to the alpine regions for a few months each summer to graze livestock. Alternatively, Loy said the data is consistent with his theory that Ötzi was a specialist alpine hunter.
"The restricted area in which he apparently lived is consistent with a home base within a valley setting," said Loy. "Most commonly, hunting/village territories are defined by the topography with boundaries along ridges and passes."
Müller said the environment of Ötzi's home range was one where farming was practiced, suggesting that Ötzi too was a farmer. This is corroborated by the types of cereal grains found with Ötzifarmed grains.
Regardless of whether Ötzi was a shepherd or specialist alpine hunter, the evidence that he spent his entire life in the region suggests to Müller that the alpine valleys of central Europe were permanently settled by the time the Stone Age came to a close.
Limestone soils dominate the landscape farther south, which are inconsistent with the isotopic signatures in Ötzi's teeth and bones, said Müller, meaning he did not spend time farther south, but rather stayed in the northern mountain valleys.
"He did not migrate there only during summer," said Müller. "That's why I think we can say the valleys were permanently inhabited. Plus, there are also a few settlements known."
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