June 6, 2012

Etched in Bone: Uncovering information about immigrants to Rome

I just returned from Holland, where I spent a lovely few days talking to all manner of experts on ancient Rome during the Moving Romans conference and thanatouring Leiden's excellent Museum Boerhaave and the Rijksmuseum van Oudheden.

My own contribution to the conference was called "Etched in Bone," and I both summarized some of my recent research on identifying immigrants to Rome (which I've previously blogged about here, here, here, and here - whew!) and expanded on that work by including some new data that, while not statistically significant, offer a look at variation within the immigrant population and let me generate new hypotheses about the lives of immigrants to Rome (hypotheses that, of course, need to be tested with more data!).

Surely the immigrant experience was not the same for everyone - after all, some immigrants were free, some were rural slaves, and some were domestic slaves.  What do these preliminary data suggest?

Demographics

The immigrant sample I'm working with has just 19 individuals.  I'm the first to admit that that's a pretty small number and certainly can't be extrapolated to the whole of Rome or the whole of the Empire.  But it would do a disservice to the study of immigrants not to explore trends and patterns, even in this small data set.

Out of the immigrants, there were 7 adult males, 3 adult females, and 9 subadults of indeterminate sex (that is, under about 16 years of age).  First, this tells us that all sorts of people were immigrating to Rome, not just young men.  This is the basic demographic chart, which interestingly enough shows a spike in the 11-15-year-old age range:

Demographics of Immigrants to Imperial Rome

Based on what we know about general subadult mortality in the Empire, kids in the age range of 0-5 have the highest likelihood of dying.  So what's going on here?  Well, what intrigues me is that I tested six individuals in the 11-15-year-old age range -- and all of them came back as non-local or immigrants.  My working hypothesis is that the large spike indicates that the 11-15-year-old age range is the time that many immigrants were coming to Rome.  We might expect a high mortality of new immigrants, those people who just completed a physically exhausting journey and have arrived at a city with a different disease ecology than their homeland.  Additional data are needed, of course, to see if the pattern holds, but we could also test third molars, which form between the ages of 12-16, to better pinpoint the age at arrival of immigrants.

Lead Poisoning and Immigrants

Another way of looking at the variation within immigrants is through lead concentrations (data from Montgomery et al. 2010).  Now, we didn't test everyone, so both the locals and the immigrants are seen in the chart below, with larger circles representing higher concentrations of lead in the first molar:

Lead Concentration in Locals and Immigrants to Imperial Rome

For reference, a lead concentration of 1 mg/kg is the current upper limit, per the World Health Organization and the Centers for Disease Control and Prevention, for kids (but there's talk of lowering the limit to 0.6 mg/kg), and a lead concentration of 10 mg/kg is the current level for "very severe lead poisoning."  It's evident from the chart that only two people had lead concentrations lower than the modern recommendation.

We know, of course, about the increase in anthropogenic lead in the Empire.  But what I'm seeing here is that locals (that is, people from Rome) were incorporating a relatively small but consistent level of lead in their bodies - a level higher than modern recommendations but much lower than severe lead poisoning.  Two of the immigrants, though, have levels over this severe lead poisoning level - it's likely they were mentally handicapped or suffered from physical or behavioral challenges because of the high lead exposure they suffered as kids.

So my current, again preliminary, interpretation of these data is that since lead use was rampant in Rome, people living there were all likely to get at least a little lead exposure in their childhoods.  But in other parts of the Empire, where the immigrants hailed from, there may have been pockets of industrial production such that some people got intense exposure to lead but others didn't.  If it becomes possible to isolate the homelands of these immigrants, it may be possible to line up archaeological evidence of the lead industry with lead concentration in the skeletons.

Porotic Hyperostosis: Diet, Malaria, or Lead Poisoning?

I've blogged before about the relationship among carbon isotopes, oxygen isotopes, and porotic hyperostosis after hearing a talk about it by Bethany Turner (whose article just came out in AJPA early view).  In short, Turner found in Peru that porotic hyperostosis - which is an indication of the non-specific condition anemia - was much more likely to be related to environment (i.e., a parasitic condition creating anemia) than to diet (i.e., iron-deficiency anemia from eating too much maize) by demonstrating that people with porotic hyperostosis had higher O values but similar C values than people without it.

What I found in the immigrant population from Imperial Rome is that all the immigrants with porotic hyperostosis were from areas with higher O values than Rome - that is, they were coming from warmer, drier climates, possibly from south of Rome in the peninsula of Italy or possibly even from northern Africa.  Yet almost all of them have similar carbon values, suggesting they were eating largely the same diet as the people from Rome:

Immigrants to Rome compared via C and O isotopes and porotic hyperostosis
(NB: triangles indicate higher Pb concentration than modern recommendations;
star indicates higher Pb concentration than severe lead poisoning)

This suggests, then, that environment rather than diet may be the proximate cause of anemia in this immigrant sample.  It makes some sense, since people coming from warmer, drier areas may have been more exposed to malaria or another parasitic condition than people living in or near Rome, which did have malaria but also had a very good, reliable aqueduct system.

Still, this is Rome we're talking about, so no explanation can be that simple.  Another factor in porotic hyperostosis is lead poisoning, which can cause severe anemia.  Again, not all of these people were tested for lead, but 4 of the 5 people with porotic hyperostosis also had lead levels over the modern recommendation.  So, there's a strong correlation among high O values, high Pb values, and porotic hyperostosis in immigrants to Rome.

It's possible that both malaria and industrial pollution affected these immigrants' health, resulting in systemic anemia that showed up in their bones.  But it definitely appears at the moment like environment was a much bigger factor in anemia among immigrants living in Rome than was their diet.

Future Prospects on Moving Romans

Lots more work needs to be done on skeletons from Rome.  There are some intrepid bioarchaeologists out there starting to work on questions and hypotheses I've outlined above, but it's quite a fertile and unexplored research field at the moment.

In the meantime, I'll be ruminating on the great questions, suggestions, and conversations I had at the Moving Romans conference, particularly as I get my article on health and disease out for publication (hopefully in a couple weeks' time) and start working up my Sr/O article for peer review.


References:

Montgomery, J., Evans, J.A., Chenery, S.R., Pashley, V., & Killgrove, K. (2010). 'Gleaming, white and deadly' : using lead to track human exposure and geographic origins in the Roman period in Britain Journal of Roman Archaeology, Suppl 78, 199-226.


Turner BL, & Armelagos GJ (2012). Diet, residential origin, and pathology at Machu Picchu, Peru American Journal of Physical Anthropology PMID: 22639369
ResearchBlogging.org

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