Whatever you call him Ötzi, Oetzi or simply the 5,300 year old Tyrolean iceman mummy found in the Alps in 1991… you can’t deny that he doesn’t have a special place in our collective curiosity. We’ve explored his fertility, his last meal, and his cause of death. Why? Well, he’s the most intact late Neolithic human we know of — preserved almost immaculately. His body and the artifacts associated with him have allowed us to peer into his everyday life and technologies.
Otzi Under The Knife
In this new paper, “Species identiﬁcation of Oetzi’s clothing with matrix-assisted laser desorption/ionization time-of-ﬂight mass spectrometry based on peptide pattern similarities of hair digests,” published in the journal Rapid Communications in Mass Spectrometry, the authors investigated the origin of the skins Oetzi was wearing before he died. As the title of the publication and specialized journal suggests, the methodology deployed was type of mass spectrometry – specifically MALDI-TOF mass spectrometry.
Mass spectrometry is a tool used to detect the molecular mass of a sample — it is especially useful in extracting the structural information of peptides and other organic compounds. I’ve used a mass spec machine in my organic chemistry courses as an undergraduate to identify small organic molecules. It wasn’t a particularly enjoyable experience. I’ve also used them in my protein chemistry classes as a graduate student to identify larger molecules.
In general, mass spectrometry devices have three parts: an ionizer, a analyzer and a detector. The ionizer adds or removes charges to the molecules studied. The ionized molecules are then separated by the analyzer, which filters molecules according to their mass (m) -to-charge (z) ratios (m/z). The detector identifies this m/z ratio.
In the current study, Matrix Assisted Laser Desorption Ionization (MALDI) was used because it is really good at dealing with molecules of high molecular mass, like proteins and peptides. A laser bombards the sample molecules in an absorbing matrix. When the molecules become ionized, they displace the matrix. The analyzer in this study, a time-of-flight (TOF) analyzer, measures the time it takes for ions in the displaced matrix to travel through a field free region known as the flight tube. The heavier ions are slower than the lighter ones.
The authors applied MALDI-TOF mass spectrometry to polypeptides from proteins off of his moccasins, coat, and leggings. We’ve known from the get-go that Ötzi’s clothing was made of animal skin — but what type of animal has been subject to debate. Some believed his moccasins were made of bearskin, indicating he was a hunter-gatherer. But if he’s wearing domesticated animals, then that’s a different story.
The MALDI-TOF mass spectrometry analysis indicated his moccasins were made of cattle. And his coat and pants were made of sheepskin. A table documenting the diagnostic m/z peaks compared to other artiodactyls and mammals from the Alps was provided by the authors. I’ve modified the table, highlighting the similarities between the two samples and the animals they matched up with. Ha 2/91 is the sample from the moccasins, while Ha 43/91/130 and Ha 6/91 were from his coat and Ha 5/91 from his pants:
Table 2. List of diagnostic peaks from selected species from the artiodactyls and their counterparts in the archaeological samples. Values of m/z in bold are used as guidance peaks for the artiodactyls. Diagnostic peak masses underlined were used as precursor ions for species identiﬁcation. The value m/z 2622 marked with (*) was only selected after MS/MS analysis
This finding indicates that at the very least Ötzi was in touch or trade with animal pastoralists. Of course, the press and authors don’t take this conservative estimate. They’re touting him as an animal herder. It is really hard to say what Ötzi’s real life story was — he’s got scraps of metal under his fingernails which indicates he was into smelting or other metallurgy. He was also found with a remarkable knife and copper-bladed axe by his side, and with that blood clot from the arrow wound and the blunt force trauma to his skull, he definately didn’t die as a peaceful shepherd or cattle herder.
If you questioned why the authors didn’t do an ancient DNA analysis of the hairs from Ötzi’s clothing, then you are not alone. Ancient DNA analysis seems to be all the rage. And for a guy that was frozen under a glacier for 5,000 years, you’d think that DNA would be well preserved. But the authors offer up a pretty convincing argument on why they didn’t do a comparative ancient DNA study. Hides that were fashioned into shoes, pants, and coats had to have been heavily processed — i.e. treated to heat and smoked, salted, soaked in urine, rubbed with animal dung, beaten, dragged over sharp sticks and/or put into herbal tanning baths for long incubation periods that would have undoubtedly damaged DNA. Protein, however, is much more resilient.
I welcome this sort of study. I’m always one for integrating new methodologies, especially from other fields… in this scenario chemistry meets archaeology. MALDI-TOF mass spectrometry, if you don’t know, has been used to check the purity of animal hair, such as Cashmere wool, and in this study it was used to figure out Ötzi’s link to a pastoralist culture.
Hollemeyer, K., Altmeyer, W., Heinzle, E., Pitra, C. (2008). Species identification of Oetzi’s clothing with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry based on peptide pattern similarities of hair digests. Rapid Communications in Mass Spectrometry, 22(18), 2751-2767. DOI: 10.1002/rcm.3679