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Ancient DNA Reveals Pulse of European Ancestry in Iron Age Philistines

NEW YORK – An ancient DNA study focused on Bronze and Iron Age samples from present-day Israel has provided a look at genetic features in the Philistines, a population portrayed as rogues in the Hebrew Bible. 

As they reported online today in Science Advances, researchers from Germany and the US sequenced more than 100 samples from an archeological site at Ashkelon, a port city on Israel's Mediterranean coast that served as a Philistine population center in the Iron Age. With genome-wide sequence data for 10 Bronze and Iron Age samples with sufficient amounts of DNA, they saw a transient influx of European ancestry during a period linked to Philistine arrival.

"This data begins to fill a temporal gap in the genetic map of the southern Levant," co-senior author Johannes Krause, an archaeogenetics researcher at the Max Planck Institute for the Science of Human History, said in a statement, noting that "the unique cultural features in the early Iron Age are mirrored by a distinct genetic composition of the early Iron Age people."

Based on variable ancestry components in the genomes, the team hypothesized that the group originated in the Mediterranean, though this European signature appeared to be all but erased in Ashketon samples from later in the Iron Age through subsequent mixing with local populations in the Levant.

"Within no more than two centuries, this genetic footprint introduced during the early Iron Age is no longer detectable and seems to be diluted by a local Levantine related gene pool," co-senior author Choongwon Jeong said in a statement.

Jeong was affiliated with the Max Planck Institute for the Science of Human History when the research was performed. He is currently a biological sciences researcher at the Seoul National University.

Ashkelon and other "Philistine" cities described in the Hebrew Bible seem to have undergone considerable cultural change in the late Bronze Age and early Iron Age, the team explained, consistent with broader patterns across Greece, Egypt, the Levant, and Anatolia. At the Philistine settlements, for example, some experts have pointed to potential "Sea People" sources in the Eastern Mediterranean for architectural features and other materials left behind after the 13th century.

"This hypothesis has been challenged by those arguing that this cultural change was driven by a diffusion of knowledge or internal development of ideas rather than by a large-scale movement of people," the authors wrote, noting that the source of incoming populations is also disputed by those who do favor the migration hypothesis.

To address these possibilities, the researchers attempted to obtain informative DNA sequence data from 108 skeletal samples excavated at Ashkelon between 1997 and 2016 through the Leon Levy Expedition, including 28 Bronze Age skeletal samples, eight samples from the early Iron Age, and 72 late Iron Age samples.

After extracting dental pulp DNA, they used in-solution DNA capture and single-end Illumina HiSeq 4000 sequencing to profile 1.24 million SNPs in 10 of the samples, dated at roughly 2,800 to 3,600 years ago — a set that included three Bronze Age, four early Iron Age, and three late Iron Age individuals.

By comparing the resulting genetic profiles with those found in contemporary individuals in Eurasia, the team placed ancient Ashkelon individuals from the time series within a broader genetic context, uncovering Iron Age genetic shifts.

While Late Bronze Age individuals shared genetic ties to other Bronze Age populations in the Levant and Anatolian and to present-day populations in the Near East, for example, the researchers saw signs of southern European and European hunter-gatherer ancestry components in early Iron Age individuals that were missing by the late Bronze Age. They noted that the European ancestry components may reflect migration from the Mediterranean, but did not rule out contributions from another uncharacterized European population.

"While our modeling suggests a southern European gene pool as a plausible source [for the European-related ancestry component], future sampling in regions such as Cyprus, Sardinia, and the Aegean, as well as in the southern Levant, could better resolve this question," the authors concluded.

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