Human cranial features, populations, and ancestry

When two different individuals have ancestry from two different parts of the world, they may differ in some features of their skulls. Forensic anthropologists have studied these differences for many years, investigating to what degree skeletal features are correlated with self-identified or socially-identified ancestry. Historically, this kind of identification was a major emphasis of forensic anthropology.

Since the advent of DNA methods, the concepts of continental ancestry and race have become less and less relevant for identification of skeletal remains. While forensic anthropologists do still collect observations on the skull and other bones, the anthroposcopic traits that they collect are placed into a context that includes systematic measurement as well as DNA analysis in most cases. The observations described here are part of the history of forensic anthropology but are less and less part of current practice.

In U.S. legal contexts, authorities or forensic specialists may need to determine the racial affinity of unidentified skeletal remains. Race is a socially defined aspect of identity that often incorporates biological characteristics such as skin pigmentation or facial features. “Socially defined” means that the race of the same person may be different in different social and cultural situations, such as different countries. In the U.S., the government contributes to defining these racial groups, collecting data in the U.S. Census and other official activities. Today, the federal government defines these groups as White, Black or African American, American Indian or Alaska Native, Asian, or Native Hawaiian or Other Pacific Islander. The government also differentiates Hispanic and non-Hispanic Whites. Many people object to this categorization, observing that it does not apply to their ancestry or self-identification. The U.S. Census relies on self-identification and an increasing number of people indicate that they identify with multiple categories.

Laws concerning race and scientific ideas have both changed since the mid-twentieth century. At that time, many forensic anthropologists viewed human races as a simple categorization of continental ancestry. In this framework, anthropologists considered ancestry as African, European, Asian or Native American. Their consideration of these groups was not only centered on identification but also on understanding the history and origins of these continental populations. Since then, anthropologists have come to understand that such continental groupings do not correspond well to the movement or origins of prehistoric populations. They have also found that the skeletal collections that early anthropologists studied—often gathered under conditions that we recognize as unethical today—do not include the extent of variation in today's U.S. population.

For these reasons, forensic anthropologists today are increasingly critical of older approaches to cranial and skeletal variation. Ann Ross and Marin Pilloud have argued that forensic specialists should abandon the idea that they can estimate ancestry and instead make assessments about an individual's population affinity: in essence, replacing a typological concept of variation with a statistical one. Elizabeth DeGangi and Jonathan Bethard have written that forensic anthropologists should abandon ancestry estimation entirely, as it sometimes can impede identification when investigators begin with the wrong assumptions about ancestry. Nevertheless, some medical examiners and forensic anthropologists continue to find value in the process of ancestry estimation. A recent study by Hillary Parsons found a very high accuracy of medical examiners' assessments of ancestry where identifications were made.  

Two things are clear in today's era of DNA identification. Cranial features are at best imperfect hints about ancestry, because self-identified ancestry is not the same as genetic ancestry, and cranial features do not reflect genes in a direct way. The other thing is that the more is known about the context of an unknown individual, the better information will be.

Here are some of the anthroposcopic traits that forensic anthropologists have studied as variations among skulls with different ancestry backgrounds. Most of them are characteristics of the face or palate.

• Shape of the eye orbits, viewed from the front. Africans tend to a more rectangular shape, East Asians more circular, Europeans tend to have an “aviator glasses” shape.
• Nasal sill: Europeans tend to have a pronounced angulation dividing the nasal floor from the anterior surface of the maxilla; Africans tend to lack a sharp angulation, Asians tend to be intermediate.
• Nasal bridge: Africans tend to have an arching, “Quonset hut” shape, Europeans tend to have high nasal bones with a peaked angle, Asians tend to have low nasal bones with a slight angulation.
• Nasal aperture: Africans tend to have wide nasal apertures, Europeans narrow.
• Subnasal prognathism: Africans tend to have maxillae that project more anteriorly (prognathic) below the nose, Europeans tend to be less projecting.
• Zygomatic form: Asians tend to have anteriorly projecting cheekbones. The border of the frontal process (lateral to the orbit) faces forward. In Europeans and Africans, these face more laterally and the zygomatic recedes more posteriorly.

Notes: Rhian Dunn and coworkers provide a recent review of ancestry estimation in forensic anthropology. They emphasize the use of anthroposcopic traits in conjunction with other approaches, including statistical software to compare measurements.

References

DiGangi, E. A., & Bethard, J. D. (2021). Uncloaking a Lost Cause: Decolonizing ancestry estimation in the United States. American Journal of Physical Anthropology, 175(2), 422–436. https://doi.org/10.1002/ajpa.24212

Dunn, R. R., Spiros, M. C., Kamnikar, K. R., Plemons, A. M., & Hefner, J. T. (2020). Ancestry estimation in forensic anthropology: A review. WIREs Forensic Science, 2(4), e1369. https://doi.org/10.1002/wfs2.1369

Parsons, H. (2021). Ancestry Estimation in Practice: An Evaluation of Forensic Anthropology Reports in the United States. Forensic Anthropology, 4(4), Article 4. https://doi.org/10.5744/fa.2020.0047

Ross, A. H., & Pilloud, M. (2021). The need to incorporate human variation and evolutionary theory in forensic anthropology: A call for reform. American Journal of Physical Anthropology, 176(4), 672–683. https://doi.org/10.1002/ajpa.24384

U.S. Census Bureau. (n.d.). About the Topic of Race. Census.Gov. Retrieved September 10, 2023, from https://www.census.gov/topics/population/race/about.html