Archaeogenetics

By applying modern genetics to population studies, archaeology, and anthropology, scientists are forming a new interpretation of prehistoric migrations. The initial peopling of Europe, Asia, and the Americas is usually explained by basic theories that appeal to reason. For example, scientists consider that groups of prehistoric peoples would periodically migrate into North America via a land bridge over the shortest span of ocean separating the continent from Asia as plausible. Answering questions such as when, and for how long, is more problematic. Archaeological field research occasionally yields new breakthroughs, but the work is painstaking and site discovery can often be a matter of chance. Scientists now address the issue in the lab rather than in the field.

Despite the density of various nations and ethnic groups in Europe, the human population of the continent is the least genetically diverse. Current anthropological interpretations of the peopling of Europe assert that the advance of agriculture was the driving force behind the migration into the region. Ten-thousand years ago, Neolithic farmers who migrated along the Mediterranean coast and then up through northern Europe were widely thought to have settled the land with their livestock and readily established farms. It was assumed that this land grab and population explosion effectively drove more primitive hunters and gathers out of the region.

Current genetic research offers a counter-thesis. Radically reinterpreting the accepted theories of a great population dispersal in Neolithic Europe, archaeogenetics suggests that Europeans are rooted in much earlier—and more primitive—peoples. The descendants of most Europeans were most likely ice age stalwarts, grouped in small, migratory hunter and gather bands. An estimated 80% of modern Europeans can potentially trace their ancestry back to one of seven female or ten male founder lineages. Such evidence suggests that not only did Neolithic farmers fail to immediately drive more primitive populations from the land, they most likely coexisted and interbred.

Archaeology and genetics can sometimes make uncomfortable neighbors—especially when more breakthrough discoveries are achieved in the lab than in the field. Over the past decade, Y chromosome research helped to narrow down possibilities for Europe's founding lineages. Y chromosome research works on one of the most basic concepts of genetics: the segregation of parental genes in offspring. The Y chromosome, which determinations the male sex in offspring, is usually passed on from father to son without any form of recombination. This segregation does not mean the gene is completely unscathed; as evolution dictates, the gene is imprinted by very minute mutations. Only 10 such genetic "tags" were observed, but were found in over 90% of the specimen.

Matrilineal studies yielded similar results. Mitochondria DNA (mDNA), passed on from mother to child, is analyzed in a similar method as its male chromosome counterpart. However, mDNA research has an added benefit. Since mDNA has an established value for mutation rates, it is useful in estimating the time scale of population change. Just as their cohorts predicted in their Y chromosome studies, mDNA evidence determined that the founder lineage for over three-fourths of Europe was in the Paleolithic era.

As with any evidence that purports to shatter existing knowledge in a field, use of both Y chromosome and mDNA has drawn many questions. Some critics worry that the data surrounding linkages with modern populations is based upon inadequate sampling. Still others doubt that mDNA is an effective standard of chronological dating. Regardless, both forms of research are making pioneering discoveries in archaeogenetics and biodiversity.

Beyond Europe, archaeogeneticists and physical anthropologists (people who study hominid fossils) Traditional Aboriginal tribal ceremony. © Penny Tweedie/Corbis. Reproduced by permission. search for increasingly primordial roots of modern populations. In 1987, scientists and mathematicians identified a theoretical 140,000–280,000 year-old source presently upheld as "Mitochondrial Eve." Though such a source is the most recent common ancestor of all humans living on Earth today, "Eve" less represents an actual human than a mathematical concept that illustrates the transfer of mDNA along a matrilineal line. As Earth's population changes over time, so too will the theoretical "Eve" mitochondrial donor. Thus, the "Mitochondrial Eve" is a crucial concept in the discussion of the genetic relationship of humans presently alive, but it is not the origin of the human species or a tangible rung in the ladder of evolution.

Studies similar to the research on the population prehistory of Europe are currently being conducted in Asia and the Americas. A skeleton found in Washington state, now known as "Kennewick Man," has yielded sever archaeogenetic clues about the peopling of North America, convincing some scientists to revisit long established population theories. However, the remains, their availability for scientific testing, and preliminary scientific studies on "Kennewick Man" remain hotly contested.