The Impact of Identity and Population History on Population Affinity Analysis in New Mexico Using Cranial Macromorphoscopic Data

Background/Objectives: This paper presents cranial MMS data for an American Indian (AI) sample from New Mexico. We compare these data to other population reference samples to understand biological distance and classification patterns. Methods: Cranial MMS data was collected from CT scans of AI individuals (n = 839) in the New Mexico Decedent Image Database. We used 12 traits following a published protocol for CT data and excluded nasal bone contour. The AI sample is compared to other samples of African American or Black, Asian, Hispanic, and White individuals to assess biological distance and classification accuracy. Results: Biological distance analysis indicated similarity among the AI, Hispanic, and Black samples, but dissimilarity among the Asian and White samples to the AI sample. Classification accuracy was low for the overall model, with Hispanic and Black individuals frequently misclassifying as AI. Conclusions: As is true everywhere, ideas about identity are complex in New Mexico. AI and Hispanic individuals in NM self-ascribe to one or both social groups. We found that biological data cannot meaningfully differentiate between these social groups, as crania are morphologically similar when examining cranial MMS traits. These results, coupled with New Mexican identity and genetics, contributes to the difficulty in group attribution in forensic casework. Nevertheless, the reference data for AI presented here can provide more robust statistics that support the likelihood of AI and Hispanic affinity in population affinity analysis. We underscore the need for an understanding of regional population history and structure and reference samples while assessing population affinity in forensic casework.