Extracting the Human Story From Our DNA--Blog

07 July 2014 Written by  Smiljka Kitanovic
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Extracting the Human Story From Our DNA--Blog Descendants of Georg Linseder: My great-grandfather Franz, railroad engineer, poses with his sons in Sarajevo, Kingdom of Serbs, Croats and Slovenes, around 1926.

New advances in DNA testing allow us to delve deeper into our ancestry than ever before.

Most of us wonder about those that lived before us. Some people go beyond mere curiosity, recording family stories and tracking down ancestors' documents. Thanks to convenient access to a multitude of records, either in archives or online databases, genealogists today are developing extensive family trees.

After becoming interested in genealogy in 2007, I spent hours examining parish records, determined to follow a line of male ancestors as far in the past as possible. My research took me back nine generations, to anDescendants of Georg Linseder: My great-grandfather Franz, railroad engineer, poses with his sons in Sarajevo, Kingdom of Serbs, Croats and Slovenes, around 1926.Grandchildren of Georg Linseder attended this schoolhouse in Sitzendorf an der Schmida, Austria, in the late 17th century. The building was previously a hospital and dates to the 15th century. ancestor who had migrated to Buda (now Budapest, Hungary) in the 1730s. Genealogists and archivists overseas helped me extend that line by three more generations, terminating with Georg Linseder who lived in Grosshaselbach, Austria, in the 17th century.

Its unlikely, though, that I'll discover any ancestors beyond Georg: oral histories and paper documents can take us only so far. Most people of European descent can't trace ancestors prior to the 16th century, when recording of baptisms, marriages, and interments was first mandated by the Roman Catholic Church. For others, the delicate paper trail ends much sooner−either because documents related to their heritage don't go far into the past, or because the documents perished in wars or unfortunate accidents.

Yet distant ancestors are not lost to us−we're all living repositories of humanity's history. In every cell within our bodies, DNA provides a molecular record that goes back tens of thousands of years into the past. We may not know the names of distant ancestors, but our DNA is showing us something much greater−that all people on Earth belong to a single human family tree.

Nowadays, learning about ancestry is easy: one can select a DNA testing company, collect their DNA sample, and send it out for analysis. Small changes in DNA, called mutations, are key for determining the relatedness and ancestry of individuals. Two people with greater differences in their DNA will have a common ancestor further in the past than two people with similar DNA. Using this new technology it will be possible to find out whether my ancestors lived elsewhere, perhaps Asia or the Middle East, during the two hundred thousand year long interim between paper documentation and the origins of humanity in Africa.

The desire to learn more about one's deep ancestry is spreading across the globe like wildfire. According to Spencer Wells, a Rhodes visiting professor at Cornell University, "consumer genomics has gone mainstream," with 2013 likely to emerge as the year of inflection for anthropological DNA analysis. In the decade preceding 2013, nearly 1 million people submitted their DNA for analysis to various nonmedical institutions. But just within the current year, another million will likely follow.

Several things have contributed to this phenomenon: DNA has become a household word, and many people today are comfortable sharing their private information. There's also the power of word-of-mouth−satisfied participants tend to pique others' interest in ancestry, and the more people who offer their DNA for anthropological analysis, the better, as it becomes easier to find DNA matches among participants.

Scientists rely on two types of DNA to unravel our distant ancestry−the Y chromosome (Ycs) and mitochondrial DNA (mtDNA). Most of our genetic material is organized into 23 pairs of chromosomes, made of tightly folded DNA and proteins. Among these chromosomes is a single Ycs, found only in men. The Ycs is passed on directly from father to son, and informs about a person's paternal lineage.

All people, however, have mtDNA. Separate from chromosomes, mtDNA is located in a small cellular compartment called the mitochondrion. But because mtDNA is passed on only from a mother to her children, it reveals a person's maternal lineage. Even though women lack an Ycs they can still learn about their paternal lineages from the analysis of their father's or brother's Ycs.

Genetic information can be used for much more than just a personal analysis of each of our own family trees, uncovering ancient migrations and intermingling between our species, Homo sapiens, and other hominins that occurred tens of thousands of years ago. Since 2005, the Genographic Project, which is led by Wells and overseen by the National Geographic Society, the Genographic Consortium and an international advisory board, has used advanced DNA analysis to understand how humans came to populate the Earth. To date, about 72,000 people from 1,000 indigenous populations contributed their DNA to the Genographic Project for this purpose. Based on variations in their mtDNA and Ycs, these people have been assigned to different groups, called haplotypes.

Study of geographic localities of indigenous peoples and frequencies of different haplotypes across the globe can help unravel many migration mysteries. For example, scientists have long been baffled by fossil records, which suggested that ancestors of indigenous Australians were among the first humans to venture out of Africa. A risky oceanic migration seemed unlikely, but paleontologists were unable to find any fossil remains suggesting a land migration across southern Asia. But when Wells and collaborators studied Ycs of southern Indians, they discovered individuals with an "M130" haplotype, which matched that of indigenous Australiansi. Ancestors of indigenous Australians most likely trekked across the coast of southern Asia, which has long since been submerged. And though fossil evidence of these early migrants is now underwater, their DNA survives in India to this day.

The newest kit offered by the Genographic Project, Gene 2.0, can also uncover other branches of the hominin family tree. Tens of thousands of years ago, we were not the only hominins roaming the Earth. Humans likely encountered Neanderthals after moving into the Middle East and Central Asia no later than 47,000 years agoii. Denisovans and humans met and mated in Asia about 45,000 years agoiii. Neither Neanderthals nor Denisovans bestowed us with much of their DNA−the mtDNA and Ycs haplotypes discovered to date are distinctly human. But a small amount of genetic material from our hominin cousins still lives on today in chromosomal DNA (other than Ycs) of some people, contributing to the wealth of our heritage.

Though my genealogy adventure revealed ancestral hometowns, professions, and families, it did not go beyond 12 generations of ancestors. My next step, submitting DNA for analysis, should eventually uncover migratory paths of thousands of nameless ancestors−human and, possibly, Neanderthal. For anyone interested in genealogy, looking deep into their DNA−and that of relatives'−allows them to go far beyond where the paper trail has gone cold. Yet unless a male Linseder descendant sends in his DNA, my ancestor Georg's Ycs lineage will remain a mystery. Far superior to the paper trail, even DNA analysis has its limitations.

i. Spencer Wells (2006). Deep Ancestry: Inside the Genographic Project. National Geographic, Washington D.C.

ii. Sriram Sankararaman, Nick Patterson, Heng Li, Svante Pääbo and David Reich (2012). "The Date of Interbreeding between Neandertals and Modern Humans." PLoS Genetics 8(10): e1002947. doi:10.1371/journal.pgen.1002947

iii. Pontus Skoglund and Mattias Jakobsson (2011). "Archaic Human Ancestry in East Asia." PNAS 108(45): 18301-18306.

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