Prehistoric Populations, Genetic Data, and Cultural Affiliation with Native American Indians

The use of genetic data in forensic science, demographic and population history, archaeology, and a variety of other disciplines has been one of the most rewarding advances in recent times. Allowing for a level of detail and traceability not found in the other methods used by these disciplines, genetic data has provided a wealth of information on population movements, cultural histories, genealogy, and on and on. In fact, the use of genetics to study population history has recently reached a milestone with the study of large genome-wide data sets that provide a wealth of information concerning contemporary and historic population relationships. However, it is not without its faults and limitations, especially when used to understand cultural affiliation among indigenous groups, such as Native American Indians. In studies of cultural affiliation between contemporary and prehistoric populations, for example, there is a dependence on much smaller-scaled data, typically from either the mitochondrial genome of the female or the Y chromosome of the male. Similarly, the datasets from these prehistoric populations is often small and spans a wide chronological or geographic range.

As such, prehistoric genetic data can provide one line of evidence to assess migration, population replacements, and cultural affiliation, but this evidence requires two levels of inference. First, the pattern of genetic variation within and between populations must be inferred from the population samples. How well these samples represent the real pattern of genetic variation within the population is a concern. Second, the underlying evolutionary process leading to the pattern of genetic variation within the population must be inferred. Among these evolutionary processes, the genetic exchange between populations is often thought to be the primary actor. However, this sort of genetic exchange is not the hypothesis most commonly used to explain structured genetic variation among prehistoric populations. Rather, the pattern of genetic variation is attributed most often to nothing more than fluctuating frequencies of variants that result from each local population reproducing and spawning the next generation. These two basic levels of inference are a major problem in using genetic data to study prehistoric population movements, demographic history, and cultural affiliation, such as those of Native American Indians.

In a recent study designed to assess whether these common inferences are correct, inferences that are found in most studies using prehistoric genetic data to study Native American Indian demographic history, Cecil M. Lewis, Jr. tested whether a few generations of isolation during periods of lower population size can explain haplogroup frequency differences.

Abstract

This study assesses whether local genetic drift within populations can be rejected as a sufficient explanation for mitochondrial DNA haplogroup frequency changes between contemporary and prehistoric population samples in the South-Central Andes. Differences in the frequencies of haplogroups between populations are a popular line of evidence for assessing population history. The null hypothesis of haplogroup frequency change is a stochastic force inherent to finite populations called genetic drift. Genetic drift is particularly influential in small populations. Innumerable historical events can result in low population sizes, and the simplest scenarios for these events are those occurring locally. In this study, simulations are used to provide a baseline for the amount of haplogroup-frequency difference expected from local genetic drift over time. The results from the simulations are compared to observed data from 23 population samples, including six prehistoric population samples. The study concludes that local genetic drift cannot be rejected when comparing a prehistoric population to a contemporary population. For the South-Central Andes, these results have dire consequences when attempting to infer genetic exchange. This study demonstrates that more informative genetic data are required for such inferences.

As this study concludes, simply a few generations of isolation during periods of low population size can cause the halplogroup frequency of the prehistoric population to change. Thus, simply relying on the hypothesis of fluctuating frequencies of variants within a population can lead to potentially faulty conclusions. Furthermore, this study is unable to reject continuity between prehistoric and contemporary populations because of this problem. As noted in the study, this raises the possibility that much of the differentiation observed between contemporary populations in the South-Central Andes – where the study focused – is attributed to events occurring after, or during, the later stages of the Late Intermediate period, essentially within approximately 750 years.

Prior to Western influence, there is no evidence that indigenous population sizes recovered from this decline. Initial Western contact likely resulted in additional population decline and fission. The spread of disease and dispersal of indigenous populations are common knowledge. Consequently, the period of small local population sizes may have extended until very recent times. What is particularly important about this study is that periods of low population size and isolation have occurred throughout the world for indigenous populations. In North America, such periods are known for the Great Basin, Southwest, and parts of the Plains and Rocky Mountains, as well as other areas. As such, reliance on genetic data to infer cultural affiliation, biological affiliation, population movements, and demographic history must be cautioned. As this study demonstrates, such reliance can lead to spurious conclusions since low population sizes and/or isolation in prehistory may result in the same conclusions. Rather, a multi-evidentiary approach is required, one that takes into account not only genetic data, but also archaeology, oral traditions, linguistics, and historic data.

The question of cultural and biological affiliation is a contentious one, and as this study indicates, genetic data may add clarification to the question, but by no means does it answer it. When it comes to prehistoric population movements and demographics, cultural and biological affiliation, and cultural histories, extreme caution is still required in reaching any conclusions.

Further Reading

 Crawford, Michael H. 2001. The Origins of Native Americans: Evidence from Anthropological Genetics. Cambridge University Press.

Jones, Peter N. 2002. American Indian mtDNA, Y Chromosome Genetic Data, and the Peopling of North America. Boulder, CO: Bauu Press.

Lewis, Cecil M., Jr. 2009. Difficulties In Rejecting A Local Ancestry With mtDNA Haplogroup Data In The South-Central Andes. Latin American Antiquity, 20(1):76-90.

Sanchez-Mazas, Alicia; Blench, Roger; Ross, Malcolm D.; Peiros, Ilia; and Lin, Marie, eds. 2008. Past Human Migrations in East Asia: Matching Archaeology, Linguistics and Genetics. New York, NY: Routledge.