The oldest human to have his complete mitonchondrial (mtDNA) genome sequenced, a 5,000-year-old “Iceman” mummy known as Ötzi, does not appear to have any living relatives in Europe. The new genetic analysis reveals that Ötzi belonged to a previously unknown branch of human evolution. Said study coauthor Franco Rollo: “Apparently, this genetic group is no longer present…. We don’t know whether it is extinct or it has become extremely rare” [HealthDay News].
The researchers extracted DNA from Iceman’s rectum. They analyzed the genome of the cells’ energy-making structures, called mitochondria. “You only get mitochondrial DNA from your mother, and she gets it from her mother and so on, so it forms an unbroken link all the way back to the common maternal ancestor of all of us,” said researcher Martin Richards [LiveScience]. Earlier studies of fragments of Ötzi’s mtDNA had indicated that he was of the K1 lineage, which is further divided into three branches. But after comparing his complete mtDNA genome with that of 115 modern Europeans of K1 lineage, the researchers found three mutations that place Ötzi in a fourth, previously unknown, branch of K1.
It’s unclear what happened to this fourth branch of the K1 lineage between Ötzi’s time and ours. Ötzi’s ancient genetic comrades may have gotten swamped by other mitochondrial DNA lines as people congregated in increasingly larger settlements, the scientists suggest. Random changes in the mitochondrial DNA of Ötzi’s peers may have contributed to the absence of a match as well [Science News]. And some scientists are skeptical of the new findings, reported in Current Biology [subscription required]. “Because the Rollo team used intestinal material from the mummy, it is difficult to exclude the possibility that their unique mitochondrial DNA lineage is a result of contaminant DNA mixing in with Ötzi’s own genetic sequences,” [Science News] said evolutionary biologist Eske Willerslev.
Nevertheless, the new genetic study contributes to our already extensive knowledge of Ötzi’s life and death. Scientists believe he lived 5,350 to 5,150 years ago as a hunter-gather and died by an arrow in his back followed by a blow with a spiked club to the face…. In 2003, researchers reported that the mummy also appeared to have suffered from heart disease, arthritis, degenerative disc disease and a bit of frostbite [HealthDay News]. In 1991, German tourists stumbled upon his mummified corpse frozen in a glacier in the Italian Alps.
Image: flickr / Alkuin