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Application of stable isotopes and geostatistics to predict region of geographic origin for deceased migrants recovered in southern Texas
Abstract and Figures
The land spanning the Mexico and US border totals 2,000 miles and experiences
hundreds of thousands of border-crossings each year by migrants fleeing violence,
seeking refuge and safety, in search of work, better healthcare, educational opportunity,
and to reunite with family (Anderson, 2008; Spradley, et al. 2008; Holmes, 2013;
DeLuca, et al. 2010). In recent years, migrants apprehended in Texas Border Patrol
Sectors consist of males and females of varying age groups traveling from Mexico,
Honduras, Guatemala, and El Salvador (United States Customs and Border Protection,
2016). The Pima County Office of the Medical Examiner (PCOME), Forensic
Anthropology Center at Texas State (FACTS), Colibri Center for Human Rights,
Argentinian Forensic Anthropology Team (EAAF), and South Texas Human Rights
Center have joined together in an agreement to share information concerning migrant
deaths with the goal of increasing the number of positive identifications and to better
understand the scope and impact of migrant deaths (Anderson & Spradley, 2016;
Spradley, 2014).
Currently, the primary methods used to estimate ancestry for unidentified skeletal
remains are craniometric (Spradley, et al. 2008) and dental morphological analyses
(Edgar, 2013), both of which are not currently capable of discerning between “Hispanics”
of different country origins. This is mainly due to “the term Hispanic [being] a social
construct with no precise genetic meaning” (Spradley et al., 2008:21). Instead, the U.S.
Census Bureau classifies all members of the Caribbean, Mexico, Central America, and
South America as “Hispanic” (Spradley et al., 2008). Promising attempts have recently
been made by Edgar (2013) to differentiate between New Mexican Hispanics and South Floridan Hispanics using dental morphological traits that are characteristic of those
populations. In some cases, the cranium and/or the appropriate teeth necessary for
ancestry estimations are not present, which prohibits either craniometric or dental
morphological analyses. For cases missing essential skeletal elements required for
ancestry estimation, stable isotope analysis can help estimate the regional geochemical
signature of the skeletal elements and dental structures that are recovered with the
individual. Stable isotopes are incorporated into the hard and soft tissues of people during
life and can be extracted after death to inform the investigator of diet and migration
patterns of the decedent. Therefore, I propose using stable isotope analyses as a tool to
estimate geographic region of residence for deceased undocumented migrants recovered
along the Mexico-US border in South Texas.
Strontium and oxygen isotope analysis can aid in the identification and
repatriation of deceased migrants by excluding possible matches and isotopically
narrowing the region of residence to specific areas within Central America, South
America, the Caribbean, as well as Mexico. The use of isotopes to help identify migrants
can be applied in conjunction with DNA, craniometric, and dental morphological data.
Isotope analysis can rule out geographic regions that do not correspond to predictions
based on isotope signatures from skeletal material. This eliminates time spent looking at
missing person reports that may match the biological profile but are not congruent with
the isotopic information for the individual.
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... Permission to use the assignment model was obtained from Wunder during the SPATIAL short-course held at the University of Utah in 2016. For greater detail concerning the assignment model, refer to Wunder et al. (2005), Wunder (2010) and Kramer (2018). ...
... Isoforensics performed all sample preparation and analyses to obtain 87 Sr/ 86 Sr and δ 18 O values. (Kramer, 2018). Strontium data interpreted as "nonlocal" to the region were omitted to reduce biases and outliers (Wright, 2005). ...
... If you are interested in seeing information about additional OpID cases and their predicted region-of-origins using the isotope assignment model, refer toKramer (2018). ...
For cases missing the essential skeletal elements required for ancestry estimation, stable isotope analysis can help predict potential regions of origin based on the geochemical signature of the bones and teeth. Some isotope systems, such as hydrogen, oxygen or strontium, distribute themselves in predictable spatiotemporal patterns and are useful geolocation tools for tracking migration of both humans and animals in Europe, Africa, Central America, South America, North America and Asia. The dual‐isotope approach for assigning unidentified deceased migrants should provide stronger results than univariate attempts. The isotope assignments provide additional evidence that migrants recovered near the US–Mexico border are a heterogeneous group, constantly migrating, that originate from a variety of regions and backgrounds. The limited isotope data for Mexico most likely influenced the inaccurate geographical origin prediction due to massive data interpolation. Isotope data and associated cultural material are powerful pieces of evidence that can greatly inform identification efforts.
... Among those positively identified, migrants from central Mexico (24%) were the most prevalent, followed by those from southern Mexico (20%), west-central Mexico (16%), and northern Mexico (14%) (Anderson & Parks, 2008;Martinez et al., 2015;Massey et al., 2002). In contrast, Texas State University's Operation Identification (OpID) reports that more individuals with Central American nationalities are recovered in southern Texas than Mexican nationals (Kramer, 2018;Spradley et al., 2019). ...
... Las firmas isotópicas locales están presentes tanto en la flora como en la fauna desde el suelo, el agua y el aire, a través de la cadena alimentaria (McLand et al., 2013). Debido a que no se produce fraccionamiento (Kramer, 2018), los valores 87 Sr/ 86 Sr reflejan los mismos valores que las fuentes de estroncio biodisponibles (Capo et al., 1998). ...
Over its fifty years of established existence beginning in 1967, the Association of Southeast Asian Nations (ASEAN) has expounded its consolidated and integrated model in political relations, economic developments, and cultural values. However, confronted by threats to global security, ASEAN has also faced the complex impacts of transnational narcotics trafficking (TransNT). The study uses grey literature as secondary data to illustrate the current situations of TransNT in Southeast Asia by way of examining drug trafficking starting from the original countries (Myanmar) through the transit points (Vietnam) to final destination countries (Malaysia). Besides reviewing more than four decades of collaboration, the paper analyses ASEAN’s milestones in building its cooperative mechanism and assesses its institutional framework for combatting TransNT with specific initiatives. The study notes the main barriers and practical challenges that constrain the process of regional cooperation. Some brief recommendations are also suggested for further research in the near future to enhance regional cooperation in combatting transnational crimes.
... Las firmas isotópicas locales están presentes tanto en la flora como en la fauna desde el suelo, el agua y el aire, a través de la cadena alimentaria (McLand et al., 2013). Debido a que no se produce fraccionamiento (Kramer, 2018), los valores 87 Sr/ 86 Sr reflejan los mismos valores que las fuentes de estroncio biodisponibles (Capo et al., 1998). ...
El artículo presenta una revisión de las investigaciones realizadas a la fecha en Colombia relacionadas con la aplicación de los análisis de isótopos en la identificación humana. En especial, hace énfasis en la utilidad de las relaciones isotópicas de estroncio (87Sr/86Sr) para rastrear el lugar de origen de un cuerpo en condición no identificada (CNI). Dentro de la revisión se resalta la importancia de la variabilidad geológica colombiana, la cual puede incidir en la diversidad del estroncio biodisponible, en un espacio y un periodo determinados. Esta diversidad del estroncio biodisponible puede verse reflejada en la distribución espacial de la composición isotópica de estroncio en diferentes tejidos humanos (dientes, huesos, cabello y uñas) de los pobladores del territorio colombiano. Esto es debido a la transferencia de la señal isotópica del estroncio biodisponible a los tejidos humanos. Dentro de las conclusiones de la revisión bibliográfica realizada se menciona la importancia del uso del estroncio (Sr) en la identificación humana en el contexto colombiano, su aplicación forense y sus posibles limitantes respecto al uso de esta metodología en el país.
... Multiisotope research has the potential to facilitate accurate sourcing in provenance studies. As examples in the circum-Caribbean region (Laffoon et al., 2017) and southern Texas (Kramer, 2018) are beginning to show, the dual-isotope method (δ 18 O and 87 Sr/ 86 Sr) is now an established technique for studies on transport and mobility. ...
Strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) has been widely used to trace human migrations across geologically distinct landscapes in archaeological, ecological, food and forensic sciences. ⁸⁷Sr/⁸⁶Sr-based provenance studies require a detailed strontium reference map to make valid interpretations of mobility patterns for a given region. In this study, we first review the previous development for ⁸⁷Sr/⁸⁶Sr isoscapes relevant to research on migration and then present the first map of bioavailable ⁸⁷Sr/⁸⁶Sr values for China, based on 1935 measurements on biosphere samples collated from published research and supplemented by our targeted collection strategy. The results show that ⁸⁷Sr/⁸⁶Sr ratios in China span a large range and exhibit regional patterns largely dependent on the divergent geological conditions of each of China's tectonic blocks. We further combined river water ⁸⁷Sr/⁸⁶Sr values with lithology, integrated elemental data, and chemical weathering rates, to determine which dominant weathering patterns (e.g. silicate, carbonate or evaporite) have the most significant influence on ⁸⁷Sr/⁸⁶Sr ratios. The low ranges of ⁸⁷Sr/⁸⁶Sr ratios (< 0.711) are predominately present in the Xing'an-Mongolian orogenic belt, which is composed of mafic-ultramafic silicate rocks, as well as in the Yangtze Block and the Junggar terrane-Tian Shan-Tarim Block, which are both influenced by the weathering of carbonate rocks. The intermediate ranges of Sr isotopes (0.711–0.7125) are mainly found in the North China Block, the northern Tibetan Plateau, and the southern Tarim Block, which may be because of evaporite dissolution and silicate/carbonate weathering processes. The high ranges of Sr isotope ratio (> 0.7125) appear in the Cathaysia Block as well as some orogenic belts and the southeastern margin of the Tibetan Plateau, likely due to the influence of the metamorphic rocks and granitoid sources. Additionally, topography, differential weathering among lithologies, and eolian deposits (e.g. loess) are also significant factors that influence ⁸⁷Sr/⁸⁶Sr ratios in China. Our study reveals that the large variation of ⁸⁷Sr/⁸⁶Sr ratios across China is predominately driven by geological conditions, revealing that future Sr isotope provenance studies can shed on ancient and historical migrations in China.
Strontium and oxygen isotope values are used in conjunction with a maximum likelihood assignment model to predict the childhood and adulthood geographic residences of 20 deceased migrants recovered along the México-U.S. border in south Texas. The objectives of this research are to determine (1) if the childhood and adulthood residency assignments predict the same geographic region, (2) if using the predicted residential history/nationality as a filter on the National Missing and Unidentified Persons System (NamUs) reduces the number of potential matching missing person reports, and (3) if we should target teeth or bone as the optimal hard tissue to sample. We found that 12 of the 20 cases (60%) predict similar regions of residency using isotopes derived from bone bioapatite (adulthood residency) and tooth bioapatite (childhood residency). When predicted residential history/nationality data were used as a filter in NamUs, there was a significant reduction in the mean number of case searches (mean = 1568.5 ± 505.3 [1 SD] vs. 107.9 ± 142.6 [1 SD]; t = 12.441, df = 22, p < 0.001, unequal variances assumed). These results demonstrate the utility of isotope data for narrowing down the region of origin and in turn the number of missing persons records to review. Finally, we recommend that death investigators at minimum collect dental samples (premolars or molars) for future unidentified migrant cases to aid in identification efforts utilizing isotope analytical methods. Bone bioapatite samples can provide more recent residential history information but should be used in conjunction with tooth enamel data.
Isoscape refinement is an essential component for accurately predicting region-of-origin in forensic investigations involving isotope analysis of unidentified human remains. Stable oxygen (δ(18) O) and hydrogen (δ(2) H) isotopes were measured from 57 tap water samples collected across Mississippi to model refined isoscapes for the state. A tap water conversion equation, δ(18) Otw =1.64 δ(18) Op-31.35, was developed for the southeastern USA to test the prediction accuracy of the δ(18) Otw isoscape using individuals with known residential histories. A local Mississippi resident (USAFA-134) was assigned with 90% probability to the correct region-of-origin reported by the participant. Assignments for Georgia residents (USAFA-118 and USAFA-205) had variable results, predicting USAFA-118 from Mississippi and USAFA-205 as a nonlocal resident. Stable isotope values often overlap geographically and a multi-isotope approach should be used when narrowing region(s)-of-origin(s). This study demonstrates the utility of refining isoscapes and the importance of tissue calibration in prediction assignments of human remains.
Substantial progress in the application of multiple isotope analyses has greatly improved the ability to identify nonlocal individuals amongst archaeological populations over the past decades. More recently the development of large scale models of spatial isotopic variation (isoscapes) has contributed to improved geographic assignments of human and animal origins. Persistent challenges remain, however, in the accurate identification of individual geographic origins from skeletal isotope data in studies of human (and animal) migration and provenance. In an attempt to develop and test more standardized and quantitative approaches to geographic assignment of individual origins using isotopic data two methods, combining ⁸⁷Sr/⁸⁶Sr and δ¹⁸O isoscapes, are examined for the Circum-Caribbean region: 1) an Interval approach using a defined range of fixed isotopic variation per location; and 2) a Likelihood assignment approach using univariate and bivariate probability density functions. These two methods are tested with enamel isotope data from a modern sample of known origin from Caracas, Venezuela and further explored with two archaeological samples of unknown origin recovered from Cuba and Trinidad. The results emphasize both the potential and limitation of the different approaches. Validation tests on the known origin sample exclude most areas of the Circum-Caribbean region and correctly highlight Caracas as a possible place of origin with both approaches. The positive validation results clearly demonstrate the overall efficacy of a dual-isotope approach to geoprovenance. The accuracy and precision of geographic assignments may be further improved by better understanding of the relationships between environmental and biological isotope variation; continued development and refinement of relevant isoscapes; and the eventual incorporation of a broader array of isotope proxy data.
Recent forensic applications of stable isotope analysis (SIA) have demonstrated its value as an investigative tool in the identification of unknown decedents. Stable isotope ratios measured in bones, teeth, hair, and nails provide a record of a person’s dietary preferences, travel history, and residence patterns. Stable carbon, nitrogen, and sulfur isotopes of human tissues provide information regarding a decedent’s dietary preferences, which in turn may reflect a person’s geographic region of origin. Additionally, stable oxygen and strontium isotopes in body tissues can be used to provenance human remains, because these isotopes reflect the source of drinking water and local geology, respectively. When combined, a multi-isotope approach provides a powerful geolocation tool for predicting a region of origin or recent travel history for unidentified human remains. In this study, we present on two forensic cases that used SIA to predict the travel history and region of origin of unknown decedents.
Fresh Fruit, Broken Bodies provides an intimate examination of the everyday lives and suffering of Mexican migrants in our contemporary food system. An anthropologist and MD in the mold of Paul Farmer and Didier Fassin, Holmes shows how market forces, anti-immigrant sentiment, and racism undermine health and health care. Holmes's material is visceral and powerful. He trekked with his companions illegally through the desert into Arizona and was jailed with them before they were deported. He lived with indigenous families in the mountains of Oaxaca and in farm labor camps in the U.S., planted and harvested corn, picked strawberries, and accompanied sick workers to clinics and hospitals. This "embodied anthropology" deepens our theoretical understanding of the ways in which social inequalities and suffering come to be perceived as normal and natural in society and in health care.
Although the typological race concept is obsolete in present-day systematic biology and anthropology, the idea that human populations and individuals are classifiable into separate races (Blacks, Whites, Native Americans, etc.) persists in government census data and mass media sources as well as in the forensic sciences. Determination of ancestry is a critical component of the forensic anthropologist's methodology in identification of human remains. In training students in laboratory techniques of personal identification, the paradox of the scientific rejection of the race concept and its survival in medical-legal contexts needs to be addressed explicitly. Forensic anthropologists and their colleagues in other branches of biological anthropology are best able to determine the ancestral background of an individual when they are familiar with the geographical distributions and frequencies of phenotypic traits in modern populations. Their methodology does not necessitate a racial classification based upon nonconcordant characters in order to provide evidence for positive identification of individuals.
Stable isotope ratio variation in natural systems reflects the dynamics of Earth systems processes and imparts isotope labels to Earth materials. Carbon isotope ratios of atmospheric CO2 record exchange of carbon between the biosphere and the atmosphere; the incredible journeys of migrating monarchs is documented by hydrogen isotopes in their wings; and water carries an isotopic record of its source and history as it traverses the atmosphere and land surface. Through these and many other examples, improved understanding of spatio-temporal isotopic variation in Earth systems is leading to innovative new approaches to scientific problem-solving. This volume provides a comprehensive overview of the theory, methods, and applications that are enabling new disciplinary and cross-disciplinary advances through the study of "isoscapes": isotopic landscapes. "This impressive new volume shows scientists deciphering and using the natural isotope landscapes that subtly adorn our spaceship Earth." Brian Fry, Coastal Ecology Institute, Louisiana State University, USA "An excellent timely must read and must-have reference book for anybody interested or engaged in applying stable isotope signatures to questions in e.g. Anthropology, Biogeochemistry, Ecology, or Forensic Science regarding chronological and spatial movement, changes, or distribution relating to animals, humans, plants, or water." Wolfram Meier-Augenstein, Centre for Anatomy & Human Identification, University of Dundee, UK "Natural resources are being affected by global change, but exactly where, how, and at what pace? Isoscapes provide new and remarkably precise answers." John Hayes, Woods Hole Oceanographic Institution, USA "This exciting volume is shaping a new landscape in environmental sciences that is utilizing the remarkable advances in isotope research to enhance and extend the capabilities of the field." Dan Yakir, Weizmann Institute of Science, Israel.
Objectives:
This analysis delivers a composite picture of population structure, admixture, ancestry variation, and personal identity in the United States, as observed through the lens of forensic anthropological casework and modern skeletal collections. It tests the applicability of the probabilistic clustering methods commonly used in human population genetics for the analysis of continuous, cranial measurement data, to improve population inference for admixed individuals without prior knowledge of sample origins.
Materials and methods:
The unsupervised model-based clustering methods of finite mixture analysis are used here to reveal latent population structure and generate admixture proportions for craniofacial measurements from the Forensic Anthropology Data Bank (FDB). Craniometric estimates of ancestry are also generated under a three contributor model, sourcing parental reference populations from the Howells Craniometric Dataset. Tests of association are made among the coefficients of cluster memberships and the demographic information documented for each individual in the FDB. Clustering results are contextualized within the framework of conventional approaches to population structure analysis and individual ancestry estimation to discuss method compatibility.
Results:
The findings reported here for contemporary American craniometrics are in agreement with the expected patterns of intergroup relationships, geographic origins and results from published genetic analyses.
Discussion:
Population inference methods that allow for the model-bound estimation of admixture and ancestry proportions from craniometric data not only enable parallel-skeletal and genetic-analyses but they are also shown to be more informative than those methods that perform hard classifications using externally-imposed categories or seek to explain gross variation by low-dimensional projections. Am J Phys Anthropol, 2016. © 2016 Wiley Periodicals, Inc.
Human children grow at a uniquely slow pace by comparison with other mammals. When and where did this schedule evolve? Have technological advances, farming and cities had any effect upon it? Addressing these and other key questions in palaeoanthropology and bioarchaeology, Simon Hillson examines the unique role of teeth in preserving detailed microscopic records of development throughout childhood and into adulthood. The text critically reviews theory, assumptions, methods and literature, providing the dental histology background to anthropological studies of both growth rate and growth disruption. Chapters also examine existing studies of growth rate in the context of human evolution and primate development more generally, together with implications for life history. The final chapters consider how defects in the tooth development sequence shed light on the consequences of biological and social transitions, contributing to our understanding of the evolution of modern human development and cognition.