Iceman May Have No Living Relatives
for National Geographic News
|October 30, 2008|
The oldest intact human mummy, the Iceman, comes from a genetic line that has either died off or become extremely rare, according to a new DNA study.
The 5,200-year-old Ötzi was discovered frozen in a glacier along the border between Austria and Italy in 1991.
Since then, scientists have investigated everything from the cause of his death at about age 46 to the material of his clothing and the contents of his last meal.
The latter study involved samples from his intestines that also included his DNA.
New analysis of a mere 0.002 ounces (70 milligrams) of this intestinal material has allowed scientists for the first time to sequence Ötzi's complete mitochondrial DNA.
Mitochondrial DNA is passed from mothers to their offspring, and although it can accumulate mutations, part of it usually remains unchanged, making it useful for tracing lineage through mothers.
(Learn about DNA.)
Mutations in Ötzi's mitochondrial DNA formed "a unique subcluster within a known European lineage," said lead author Franco Rollo of the University of Camerino in Italy.
However, the Iceman's line became, "if not extinguished, extremely rare" during the last 5,000 years, Rollo said.
The research was published online today in the journal Current Biology.
Ötzi possessed the oldest modern human mitochondrial genome produced so far, noted co-author Martin Richards of the University of Leeds in the U.K.
"His lineage actually diverged from its nearest modern relatives about 20,000 years ago, by the looks of it," Richards said.
The scientists plan to look at the Iceman's Y chromosome DNA, which is passed on by fathers.
"He would never have had any [direct] descendants on the mitochondrial DNA side anyway, because he's a man," Richards said.
The mitochondrial DNA at best could link him to distant relatives—descendants of a sister or aunt, perhaps.
The scientists also plan to gather more genetic lines from people living in the region.
"At the present state of knowledge, no one can claim to be the descendant of Ötzi, but who knows " Rollo said by email.
Not That Surprised
Anne Stone of Arizona State University has studied the Iceman's DNA but was not involved with this study.
She said the work is interesting, but the complete genome of only one sample limits what can be gleaned—a concern the study authors share.
"I am not that surprised that his lineage is somewhat different from other European lineages and may have died out," Stone said.
I am sure that as additional complete mitochondrial genomes from Europeans of similar lineages are sequenced, we will know more about how his fits in with modern sequences, she said by email.
(Explore a time line of human migration.)
"I don't know that similar sequences will necessarily be found in the Alps," she said, adding that "there has been a lot of migration over the last 5,000 years."
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