Before I decided to go into biomedical science, I wanted to be an Egyptologist. Inspired in part by Indiana Jones, I had grand notions of adventure and discovery in the Sahara Desert. The pyramids, the Sphinx, ancient hieroglyphics, and pharaohs – these all fascinated me, but none as much as mummification, a ritual that preserves the body for traveling into the afterlife where it reunites with the soul. A new study, published in May in Nature Communications, has now unlocked another secret of the past hidden in the DNA of ancient Egyptian mummies. As an amateur historian of ancient Egypt and a trained scientist who studied viral genetics, this discovery immediately caught my eye.
The first Egyptian artifacts I saw up close were at the Cleveland Museum of Art. The Coffins of Bakenmut (c. 1000-900 BC) and his wife Nesykhonsu (c. 976-889 BC) were two of the most memorable pieces because of their intricate painted details that held fast over thousands of years. As a member of the clergy of Amun, the patron deity of Thebes, Bakenmut was laid to rest in a lavishly decorated coffin befitting his stature, complete with images of the deified pharaohs Tuthmosis III and Amenhotep I. Nesykhonsu’s coffin is more personally illustrated with scenes from her own funeral, including depictions of the rising and setting sun, which serve as a metaphor for her life. I remember gazing in awe at the ancient Egyptians’ ability to tell a story through artistic symbolism, one that lasts over centuries as a relic of past human civilization.
Although I didn’t see a mummy until later in life, during visits to other museums like The Met and The Smithsonian, I appreciated the sacred, meticulous process of classic mummification. Under the guidance of the jackal-headed god Anubis, priests and embalmers worked diligently over a period of 70 days performing the ritual. They first removed the brain through the nose, emptied the body of its internal organs, and dried the body with chemicals and long-term exposure to air. Finally, the desiccated body was wrapped in a cocoon and wreathed in a linen shroud. Depending on the time period and one’s social status, mummies were covered with a mask and placed in a wooden or stone sarcophagus, sometimes in multiple, nested layers. Mummification resulted in a well-preserved body, complete with intact facial features, clues about health and disease, and even whole tattoos. Yet, despite the overall maintenance of gross anatomy, thousands of years spent in the hot Egyptian climate and certain chemicals used in mummification contribute to DNA degradation. Many were skeptical about the long-term preservation of mummy DNA, until now.
Like most, I learned about the basics of DNA in biology class. During my tenure at the National Institutes of Health and then in graduate school at the University of North Carolina, I studied viral infection using laboratory techniques to acquire the sequences of DNA encoding the pathogen’s genes. One such methodology at the forefront of current genetics research is called ‘next-generation’ or ‘deep’ sequencing. Using this technology, a group of scientists recently demonstrated that genetic data preserved in mummy DNA could be extracted to examine ancient Egyptian ancestry. The DNA was harvested from the teeth and bones of 90 Egyptian mummies excavated from the ancient town of Abusir el-Meleq.
The authors, Johannes Krause and his colleagues, were able to parse the genetic data hidden within the ancient genomes and compare the mummies’ DNA with modern and ancient populations in Africa and Europe. They found that the ancient Egyptians shared more ancestry with Near (Middle) Easterners than with present-day Egyptians. This genetic discrepancy arose from the introduction of sub-Saharan African DNA into Egypt roughly 700 years ago, which may have occurred through increased trade or immigration. Mixing of these ancient populations resulted in modern Egyptians having inherited 8% more African ancestry than the Egyptian mummies.
The mummies from Abusir el-Meleq spanned roughly 1300 years of ancient Egyptian history, being radiocarbon dated to the late New Kingdom and into the Roman Period (1388 BC and AD 426). Despite the likelihood of foreign presence in Abusir el-Meleq during this time period, the mummies were quite genetically consistent, meaning that they had limited evidence of foreign ancestry. Krause and his colleagues propose that such an influence may be more apparent in other regions where Greek and Roman settlements were more concentrated. Societal pressure to marry within one’s ethnic group could have also affected the mummies’ genetic continuity, especially for citizenship reasons during the Roman era.
What sets this study apart from others is the quality of the data obtained. As a scientist, one quickly learns the importance of solid data. It’s not always easy to obtain, and nothing hurts quite as badly as a failed experiment that took hours upon hours to perform. Yet, with perseverance and a bit of luck, an elusive question can be answered.
Previous studies of mummy DNA have faced criticism over their use of older, less sensitive techniques with greater potential for error, including the detection of contaminating DNA. Recent work characterizing the genetics of King Tutankhamun’s family also falls prey to these questions of authenticity. Through the use of improved methodologies and the inclusion of rigorous quality checks, Krause’s team provided compelling evidence of the ancient origin of the DNA they examined. They did so by looking for characteristic genetic features of ancient DNA and performing statistical contamination tests. In the end, they obtained well-preserved mitochondrial DNA from 90 mummies.
Mitochondrial DNA is different from the DNA housed within a cell’s nucleus, the latter of which is more commonly referred to when learning about heredity. In contrast to nuclear DNA, which is comprised of genes spanning the entire human genome that are passed down from both parents, mitochondrial DNA is inherited solely from the mother and includes a small number of genes existing in many replicates within the cell’s mitochondria. The latter is more easily harvested from ancient remains because of its greater number of gene copies. Of the 90 mummies from which Krause’s team obtained mitochondrial DNA, only three yielded nuclear DNA of sufficient quality. Despite having few full genomes to examine, the breadth of genetic information that these three mummies provided is an exciting find.
An overarching question remains as to whether the mummies excavated from the town of Abusir el-Meleq are representative of the greater ancient Egyptian population. The genetic picture may change depending on the location of the population studied, even within the same timeframe. More work is required to address this question. With thousands of mummies archived in museums and the means to analyze their ancient genomes, our understanding of human ancestry will continue to be shaped in the coming years. Perhaps a foray into Egyptology is ahead of me after all…
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