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Old Seeds Coming in from the Cold

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Science  19 Dec 2008:
Vol. 322, Issue 5909, pp. 1789-1790
DOI: 10.1126/science.322.5909.1789b

S. Sallon and colleagues (“Germination, genetics, and growth of an ancient date seed,” Brevia, 13 June, p. 1464) reported the successful germination and growth of a 2000-year-old date seed excavated from underneath a Herodian fortress near the Dead Sea. On the basis of radiocarbon dating of additional seeds recovered from the same excavation as well as seed remains recovered when repotting the palm seedling, S. Sallon et al. claimed to have found the oldest seed with the ability to germinate.

However, Sallon et al. overlooked a report on a considerably older germinable seed, published in Science more than 40 years ago (1) [although the paper did appear in the bibliography of one work cited by Sallon et al.: Shen- Miller et al. (2)]. Porsild and co-workers convincingly showed that a seed of the arctic lupine (Lupinus arcticus), stored in a lemming burrow since the Pleistocene, could still be germinated. These authors estimated that the seed was at least 10,000 years old, based on the stratigraphic inference of the overlaying frozen silt deposit. Analogous to the dry climate that conserved the date seed, frozen ground provides excellent storage conditions to retain seed viability.

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Response

Gugerli claims that arctic lupine (Lupinus arcticus) are the oldest seeds to be germinated. Much controversy exists over reports of extreme seed longevity under “natural” conditions (as opposed to ex situ storage and conservation of seeds in gene banks). Claims that have been viewed skeptically include alleged viability of ancient cereal grains from Pharonic tombs (1); Chenopodium album and Spergula arvensis from a 1700-year-old site in Denmark (2); Nelunbo nucifera seeds associated with a 3000-year-old canoe near Tokyo (3); and, most extreme, Lupinus arcticus seeds retrieved from rodent burrows allegedly dating to the Late Pleistocene period (4). In all of these reports, seed dating relied on their association with archaeological artifacts, circumstantial evidence that makes the claims extremely questionable (1, 58).

The age attribution of the arctic lupine seeds, unearthed 3 to 6 meters below the surface of frozen silt during 1955 mining operations in the Canadian Yukon, was based partly on the identification of a rodent skull also found in the burrow. The modern relative of the Dicrostoyx groenlandicus rodent species is apparently found in cooler regions, and the authors assumed that the overlying silt had been frozen during an unspecified geophysical catastrophe. The supporting radiocarbon date of 14,860 ± 840 relates to the nest and remains of an Arctic ground squirrel recovered from burrows similarly buried under permafrost in central Alaska (9, 10).

Without radiocarbon dating of any of the two dozen arctic lupine seeds recovered from the burrows, unequivocal evidence for the contemporaneity of the seeds is lacking. In our Brevia, the claim for germinating a 2000-year-old date seed was based on direct radiocarbon dating of seed coat fragments from the seed itself and indirectly on two ungerminated date seeds from the same archaeological site and locus. Therefore, although we have not claimed that this is the oldest viable seed, it is the oldest seed in which germination has been documented based on validated direct radiocarbon evidence.

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