Genetic Data, Cultural Affiliation, and Prehistoric Populations: What We Know and Don't Know

Prehistoric Populations, Genetic Data, and Cultural Affiliation wit...

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.

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Comment by Peter N. Jones on June 6, 2009 at 2:51pm

Good questions. I'll try and answer them as succinctly as I can, but really they are much more involved then the space here allows.

Yes, there is very good genetic evidence demonstrating that a population (or populations - see here for information on the prehistoric waves of migration into the Americas) migrated into the Americas from Asia some 20,000-15,000 years ago. The genetic data, either based on the father (Y Chromosome) or mother (mtDNA) argues for a couple of places of origin in Asia that led to the populations that eventually migrated across the Bering Straits and into the Americas. The biggest problem with the genetic data is that there is really no - or limited - evidence from other data sources: archaeology. The archaeological evidence can be used to support the same migration and time periods, but it is not as conclusive.

Does this negate the possibility of a population being present before the migration in the Americas? No, but there has been no archaeological nor genetic evidence to support such a possibility.

There is no evidence of movement of people directly across the Arctic Circle. All evidence suggests a movement from northern Asia across the Bering Straits (by land and boat) into Alaska. From there, evidence suggests that people moved either down the North American coast via boats until they got to about present-day Oregon, at which point they could then move inland up the various river corridors (Columbia River, Fraser River, American River, etc.), or they moved inland across the Canadian shield and down into the Americas on the eastern side of the Rocky Mountains (after the Laurentide ice sheet melted).

As for you last question, the correct answer is no, but people are trying. As you can see from the article above on genetics, prehistoric populations, and cultural affiliation, there are too many factors and unknowns to take today's genetic profile and extrapolate that back in time to try and estimate population size. One can try and estimate the haplogroup frequency (the percentage of certain alleles that appear in the population), but even that is fraught with problems. There is no "clock" that can be used to extrapolate genetic mutation, thus allowing for the timing of population growth. There have been various "genetic clocks" developed, but they are very crude in their resolution, and have only been used to try and estimate various hominin gene splits.

Hope that answers your questions.


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