The researchers' case that the Gilgal fruits were deliberately cultivated rests on an idiosyncrasy of fig genetics.
Normally, pollination by specialized wasps is required for fig trees to bear edible fruit.
Occasionally, however, a mutation occurs that allows fruit to develop from unfertilized female flowers, a process known as parthenocarpy.
Some figs grown commercially today are of this variety. Apparently, so were the Stone Age figs at Gilgal.
Microscopic analysis revealed that the figs lacked embryonic seeds, a distinguishing feature of the mutant form, in which fruit are produced without pollination.
"The mutation does not survive in nature more than a single generation," Kislev said.
That means the fig trees at Gilgal could not have been reproducing naturally.
The large cache of fruit fragments recovered from the site suggests that humans were maintaining the mutant trees by planting live branches in the ground.
Kislev says fig trees are particularly amenable to this common horticultural technique, called vegetative propagation.
Additional fig remains have been recovered from other sites throughout the Middle East, and at least some appear to be of the Gilgal variety.
To Kislev, this suggests that choice trees were being transported and planted to increase agricultural yield at different locations.
"The early propagation of fig trees, if true, has a rather important effect on the way we view the Neolithic [or Late Stone Age]," said archaeologist Joy McCorriston, of Ohio State University in Columbus.
The Neolithic is a loosely dated period of cultural development marked by the invention of agriculture, improved stone stools, and sedentary village life.
McCorriston notes that although planting shoots of fig trees may be simple, early fig farmers would have had to wait several years for their reward.
This suggests relatively long-term ties to land and perhaps new social and economic arrangements prior to the full-scale adoption of an agricultural lifestyle.
"Ownership of trees [may have] provided a way of mapping society onto physical space," McCorriston said.
As objects of long-term interest and care, fig trees may also have had symbolic significance.
Archaeologist Bruce Smith of the National Museum of Natural History in Washington, D.C., says early fig cultivation is indicative of a general atmosphere of experimentation following the last ice age.
"Human societies were auditioning a wide range of species" for a role in the unfolding drama of agriculture, Smith said.
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