The Footsteps of the First Americans

Instructor’s Comment: Kevin Dumas’s lay audience essay was the culmination of a series of assignments on the same topic that led to this final version Kevin intended for the National Geographic. Having worked on the research parts of the topic in earlier papers, Kevin wanted to write a piece that the general public would enjoy without compromising the scientific complexities of his topic. In his writer’s note to me, he explained that he wished to “take time to simplify the science behind genetic markers and to create genetic maps,” but he also intended to write for a scientifically-savvy audience; finally, by bringing his interest in Anthropology into the mix, Kevin wrote his fascinating narrative entitled “The Footsteps of the First Americans.”
—Aliki Dragona, University Writing Program

Who discovered America? If you took a random poll asking U.S. citizens this question today, you would likely hear “Christopher Columbus.” Indeed, this is what many of us were taught in grade school—Christopher Columbus stumbled upon the New World while blazing a trade route to India. However, to say Christopher Columbus discovered America is to disregard the existence of the people Columbus encountered upon landing in the Americas. At the heart of the matter, our appreciation and glorification of Christopher Columbus is merely an extension of the axiom that history is written by the winners.

The truth is, Christopher Columbus wasn’t the first person to see America. In all likelihood, the crewman sitting in the crow’s nest of the Santa Maria saw the New World before his esteemed captain. Before that, the Vikings and Russians are believed to have explored portions of the New World. None of them, however, were the real first Americans. In fact, it would be more appropriate to categorize these people as the “first tourists.” Who, then, were the first Americans? When did they arrive? Where did they come from? The general answers to these questions have been known for a long time—they are effectively the big pieces of a puzzle salvaged at archeological and geological sites across the Americas. While these big pieces provided scientists with a great deal of information, the puzzle has remained perpetually out of focus. Smaller, vital details were needed for finer theories to emerge, but such details have long been considered lost to time. Fortunately, recent developments in the biotechnology industry have refined the technologies required to finally discover the smaller fragments of this amorphous puzzle. Incredibly, these new pieces were not gleaned from the earth like the first pieces, but from our own bodies.

Much of what we thought we knew about the first Americans came from a theory called “Clovis First.” This theory was developed in the early 1930s when several archeological sites were found across the Southwest United States.(1) One such site, found outside of Clovis, New Mexico, was determined to be around 11,000 years old. Archeologists knew of no older archeological site in the Americas and thus assumed that the people who inhabited the Clovis site, and the accompanying sister sites, were the earliest Americans.(1) Even as evidence of earlier human habitation popped up in both North and South America, the general aspects of the Clovis First theory lingered in the opinions of American anthropology experts, often to the detriment of more developed theories. 

Evidence mounted until it became obvious the Clovis First theory was incomplete. Unfortunately, experts had run into a dead end with archeology. Although there was plenty of evidence that humans had inhabited the Americas longer then 11,000 years—as seen at sites like Monte Verde—evidence concerning the migration to and within the Americas remained limited.(1) Experts turned to scientists in other fields for help. The most fruitful work was done by geneticists who realized that contained within our DNA was not only the blueprint for our body’s structure and function, but the footprints of our ancestors.

While the majority of the human DNA sequence, or genome, is shared between individuals, ultimately our DNA is unique to each of us; no two individuals have the exact same DNA sequence. The differences in our DNA emerge from what are called mutations. These mutations accumulate at a very slow rate and are occasionally passed on to the next generation. While mutations are often viewed with fear or anxiety because of negative connotations associated with radiation and genetic diseases, mutations can prove to be an incredibly useful genetic tool. Nowhere is this more apparent than in the case of evolutionary anthropology, where the retention of randomly inherited mutations can be used to determine the movements of the earliest Americans.

To determine just how humans migrated into the Americas, scientists employed genetic markers. Genetic markers are known, recognizable DNA sequences that can be used for analytical purposes.(6) Such markers exist across the genome and are often classified into three categories: Autosomal markers, Y-chromosome markers, and mtDNA markers. Autosomal markers are markers that exist in the DNA that is shared between sexes. Y-chromosome markers, on the other hand, are markers that lie exclusively on the Y-chromosome. Because of their location, Y-chromosome markers are only found in males and thus have a surprising amount of utility. The last category of markers, called mtDNA markers, exist in sub-cellular, power generating structures called mitochondria.(6) Because of an ancient symbiotic event, mitochondria have their own unique DNA. This DNA, like normal DNA, is subject to mutation over time. However, because mtDNA is not exposed to proteins that fix mutated or damaged DNA, mtDNA accumulates mutations unusually fast. Additionally, unlike the rest of our DNA, which is comprised of DNA segments from both parents, mtDNA is inherited solely from the mother. As such, mutations found in mtDNA are easy to access and track over several generations.(5)

This principle of passing of mutations to future generations is incredibly useful to evolutionary anthropologists—the older the mutation, the more people that will carry it, and vice versa. Using this fact, anthropologists can look at mutation frequencies in Native Americans today to determine the age of various mutations in autosomal DNA, Y-chromosome DNA, and mtDNA.(3) Putting together the ages of several accumulated mutations allows for the development of a genetic migration-map for early Americans. Furthermore, by looking at genetic differences between Native Americans and Asiatic ethnicities, scientists can determine how old Native-American-exclusive mutations are and, consequently, determine the date of migration into the Americas and subsequent movement within the Americas.

The advent of molecular genetics technology has yielded a wealth of new information for evolutionary anthropologists and genetic scientists alike. This information has served as a foundation for several new theories concerning the migration date into the Americas.(8) Comparison of data from mtDNA in Native Americans and the natives of Siberia led scientists to believe that the major migration(s) consisted of anywhere from 1,000 to 2,000 individuals.(5) mtDNA evidence indicates these event(s) happened around 25,000 years ago.(6) However, Y-chromosome data taken from the same sample set indicates the migration(s) occurred closer to 15,000 years ago.(6) Such a large discrepancy indicates the mapping techniques and mathematical models being used for analysis remain in their infancy. Additionally, a great deal of error could also be attributed to fundamental flaws in the genetic formulas being used for the accumulation and spread of mutation frequencies. Unfortunately, we encounter a paradox in such formulas—for accurate models to be created, we must have an independent source to help structure the model. In the case of evolutionary anthropology, genetics is the independent source. As such, scientists must make the best guess possible while also allowing room for changes as new population models and information become available.

Applying the same genetic markers and mutation frequencies used to determine the time of entry into the Americas, scientists managed to determine which Asian population gave rise to the Native Americans. This population was found to be a small society on the eastern edge of Siberia.(7) Scientists later concluded this group had originated from tribes in Mongolia and lived in relative isolation several thousand years prior to entry into the Americas. The mutations accumulated in this isolated lineage were passed on to all Native Americans.(7) Interestingly enough, changes in these characteristic mutations are more common in Native American populations located further from the Northwestern tip of the Americas. This finding lends support to the theory that Native Americans entered the Americas through an overland passage in what is now Alaska.(7) 

Scientists who used mtDNA and Y-chromosome genetic data to propose a 15,000 to 25,000 YBP (years before present) entry into the United States encountered a large problem that the Clovis First theory did not—glacial ice sheets. Geological data shows that the last glacial maximum, or the time when ice age glaciers had grown to their largest size, was around 20,000 YBP.(4) Anyone trying to migrate into the Americas from Asia during this period would have made it to the current location of Fairbanks, Alaska, before encountering an inhospitable ice sheet spanning hundreds of miles into the American interior.(1) This impassible terrain would have prevented entry into lower North America until several thousand years later, when the glaciers receded and an inland route leading to what is now Montana formed. Supporters of the Clovis First theory originally cited this evidence as proof of their argument. However, updated geological records coupled with genetic data taken from the Pacific Coast suggest early Americans migrated down a very narrow Pacific coast corridor present during the last glacial maximum4. It is now thought that this coastal-migration lifestyle could have been so successful for supporting human expansion that it was used to migrate all the way into South America around 14,000 years ago.(4)

While new developments in technology have given scientists an incredible amount of new information to utilize, methods for analysis are still being developed. The vast influx of data, along with specialized data sets and new (but untested) population models, create a great deal of uncertainty and error in each new migration model proposed. Fortunately, as time passes, more archeological sites and genetic testing methods will allow for the creation of a comprehensive model encompassing both the migration into the New World and the later colonization of the American landmass.

Literature Cited
1.    Begley, S. and A. Murr. 1999. The first americans. Newsweek. April 26, 1999.
2.    Goebel, T. et al. 2008. The late Pleistocene dispersal of modern humans in the Americas. Science 319: 1497–1502.
3.    Hunley, K. L., J. E. Spence, and D. A. Merriwether. 2008. The impact of group fissions on genetic structure in native South America and implications for human evolution. American Journal of Physical Anthropology 135: 195–205.
4.    Lewis, C. M. et al. 2007. Mitochondrial DNA and the peopling of South America. Human Biology 79 (2): 159–178.
5.    Mulligan, C. J., A. Kitchen, and M. M. Miyamoto. 2008. Updated three-stage model for the peopling of the Americas. PLoS ONE 3 (9): e3199.
6.    Schurr, T. and S. Sherry. 2004. Mitochondrial DNA and Y chromosome diversity and the peopling of the Americas: evolutionary and demographic evidence. American Journal of Human Biology 16: 420–439.
7.    Wang S. et al. 2007. Genetic variation and population structure in Native Americans. PLoS Genetics 3 (11): e185.
8.    Wilson, J. A. P. A new perspective on later migration(s): the possible recent origin of some Native American haplotypes. Critique of Anthropology 28: 267–279.