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Early Domesticated Fig in the Jordan Valley

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Science  02 Jun 2006:
Vol. 312, Issue 5778, pp. 1372-1374
DOI: 10.1126/science.1125910

Abstract

It is generally accepted that the fig tree was domesticated in the Near East some 6500 years ago. Here we report the discovery of nine carbonized fig fruits and hundreds of drupelets stored in Gilgal I, an early Neolithic village, located in the Lower Jordan Valley, which dates to 11,400 to 11,200 years ago. We suggest that these edible fruits were gathered from parthenocarpic trees grown from intentionally planted branches. Hence, fig trees could have been the first domesticated plant of the Neolithic Revolution, which preceded cereal domestication by about a thousand years.

New archaeobotanic evidence seems to indicate that fig cultivation was widely practiced in the Near East during the 12th millennium before the present (B.P.), nearly a thousand years before the domestication of cereals and legumes. The origin of the common fig (Ficus carica) is still an unsettled issue, though some of its major steps have been reconstructed (16). Finds include fruit fragments and drupelets from Gilgal I (Fig. 1 and figs. S1 to S3), an early Neolithic site in the Jordan Valley, as well as from a number of other Neolithic sites of similar age (1, 711). Figs in these early archaeological sites significantly outnumber any other fruit remains from that period. This successful human initiation was probably due to the simplicity of fig tree propagation, which is achieved by merely cutting and planting branches (12). Small genetic changes in wild figs occurring at that time considerably improved the fruit's taste. These two characters may explain why the domestication of the fig preceded that of other fruit trees, such as the grape, olive, and date, by almost five millennia (13).

Fig. 1.

Carbonized fig fruit (Ficus carica var. domestica) from Gilgal I, broken lengthwise. Orifice (A) surrounded by scales (B). The fruit skin (C) covers the thin fruitflesh (D) and its inner part (E), which includes the empty drupelets (F). Scale bar, 5 mm. [Panoramic scanning electron microscope micrographs by Y. Langsam]

The common fig is a gynodioecious species composed of two sexes: the hermaphroditic inedible caprifig, which is functionally a male fig (F. carica var. caprificus), and the edible female seed fig (F. carica var. domestica). The hermaphroditic tree produces both male staminate flowers and female pistillate flowers within each fig syconium, whereas the female variety has only pistillate flowers. There is also a widely grown parthenocarpic variety of female fig, in which the ovaries develop into drupelets without pollination and fertilization.

The fig tree, whose fertilization is carried out by the symbiotic fig wasp Blastophaga psenes (fig. S4), produces three crops during the year: in early summer (June-July), in midsummer-autumn (August-November), and in early spring (March). The polleniferous spring hermaphroditic figs are the main source of wasp-borne pollen, but the syconia of the remaining two crops produce little or no fertile pollen. They function as domiciles in which the short-lived wasps propagate (14).

The syconium is an enclosed inflorescence that transforms into a hollow receptacle. Whereas the syconia of the hermaphroditic caprifig produce minute staminate flowers and pistillate flowers with a short style (2 mm long), the syconia of the female fig tree produce only long-style (3 mm long) pistillate flowers. Style length has a crucial role in the fertilization process, because the minute fig wasp has an ovipositor 2 mm long. After emerging from its native syconium, the flying wasp, coated with pollen, enters through the orifice (ostiole) of a young syconium on a different tree. When meeting the short-style flower in a hermaphroditic tree, the wasp successfully inserts its egg through the style into the flower's ovary. As a result, a larva develops that feeds on the developing tissue and emerges through a hole in the wall of the ovary container as an adult male or female (Fig. 2 and fig. S4). But when the wasp enters syconia with the long-style flowers of the female tree, oviposition fails because the ovipositor is too short. The female flowers are nevertheless pollinated and set normal seeds (2, 15).

Fig. 2.

Modern hermaphroditic fig fruit (F. carica var. caprificus) from Kalambaka, Greece, in length section. The orifice (A) is furnished with many scales (B) along its length. The fruit skin (C) covers the spongy fruit flesh (D); the inner part (E) includes many drupelets that exhibit holes through which fig wasps emerged (F). A few wasp males remained within the syconium (G). The stamens (H) are observed below the orifice. Scale bar, 2 mm.

Sex determination in the common fig appears to be controlled by two closely linked pairs of alleles on an unidentified pair of chromosomes. They are represented as follows: A is a dominant allele for the presence of male flowers in the syconium, and a is a recessive allele for the suppression of male flowers; G is a dominant allele for female flowers with short styles, and g is a recessive allele for female flowers with long styles. So, the caprifig homolog is GA and genotypes of caprifig trees are GA/GA or GA/ga. The female homolog is ga, and the trees always have the genotype ga/ga (3).

Both genetically homozygous (GA/GA) and heterozygous (GA/ga) hermaphroditic types produce spongy inedible fruits with flowers that turn into wasp-hosted galls (3) (Fig. 2). When caprifig syconia (GA) ripen in the spring, they produce wasps and pollen but are unable to produce fertile seeds: the mother wasp entering the young caprifig syconium emerged from a midsummer-autumn syconia crop that does not produce pollen. If, however, the winter-developing caprifigs are fertilized artificially by humans, they produce ripe fruits that are somewhat smaller than those of the unfertilized wasp-populated caprifigs. This results from the considerably smaller intercellular spaces in the flesh of the wasp-free fruit than in the wasp-inhabited caprifigs (14). Heterozygous wild trees (GA/ga) can also generate female fig trees with long functional pistillate flowers (ga/ga) that produce fertile seeds (3, 16).

In contrast to seed-producing figs, a second kind of fig tree with edible fruits is a mutant that generates figs with embryoless drupelets by parthenocarpy (development of the ovary without pollination or fertilization). These figs become soft, sweet, and edible because of the persistence of the unfertilized syconia on the tree; this process differs from that in nonparthenocarpic female types, which shed their syconia when unfertilized. This parthenocarpy can be merely vegetative or, in other varieties, can be induced by the stimulus of the female Blastophaga inserting her ovipositor into the style of the female flower without oviposition. This stimulation prevents dropping of the fruit, allowing it to develop to maturity. Parthenocarpy, which results from a single dominant mutation P, is known to occur in hermaphroditic as well as in female figs (3, 17); it could have also occurred in the predomesticated fig. Because both parthenocarpic hermaphroditic and female fig trees do not set germinative seeds, they are reproductive dead ends unless humans interfere by planting shoots of these parthenocarpic trees.

We found nine carbonized fig fruits as well as 313 single drupelets, dated between 11,400 and 11,200 years B.P., at the early Pre-Pottery Neolithic A (PPNA) Gilgal village site in the Lower Jordan Valley (Fig. 1). The Gilgal figs are rather small, ∼18 mm in diameter, but are ripe, with full-sized drupelets: 1.0 to 1.4 mm. The carbonized figs were not distorted, implying that they were most probably dried purposely for human consumption. They were found broken into large pieces, revealing their flesh, drupelets, and orifice (Fig. 1 and figs. S1 to S3). Dried figs similar in size and structure imported from Iran are found today in the markets of London. However, the Gilgal figs differ from those of F. pseudosycomorus grown in neighboring regions. Fruits of the latter species are crowded by wasps and are 10 to 15 mm in diameter, even smaller than the Gilgal variety (18).

More than 100 of the 313 individual drupelets from ripe fruits were inspected, and most of them were embryoless or had an undeveloped embryo, which reflects parthenocarpy (fig. S3). Such parthenocarpy is observed today in various cultivated fig varieties (fig. S5) (3, 4). It is impossible to distinguish morphologically between fertilized and unfertilized drupelets (19). The small number of drupelets whose cavity seems to be occupied by an embryo (fig. S3) may reflect a natural variation in unfertilized embryos. Alternatively, they might have been fertilized, but their embryo development was arrested before producing full, ripe seed.

The few drupelets that seem to contain an embryo could also be explained by a small number of fertilized drupelets that appeared in a hermaphroditic fig that accidentally produced fruits. This could happen when the wasp population was not large and a single pollen-coated wasp fertilized a small number of short-style female flowers that were not oviposited (4, 13, 20). However, this proposal is unacceptable because no evidence of stamens was observed in the fossil evidence from Gilgal, and not a single drupelet shows any sign of a wasp or wasp exit (compare Fig. 1 to Fig. 2). We therefore conclude that all these remains are of a parthenocarpic variety of F. carica.

The large assemblage of parthenocarpic figs uncovered in Gilgal provides early evidence for fig horticulture via vegetative propagation. Once the parthenocarpic mutation occurred, humans must have recognized that the embryoless fruits do not produce new trees, and vegetative fig tree cultivation became a common practice. Additional fig remains are reported from other early Neolithic sites in the Levant (Table 1) (710, 21). To confirm our results from Gilgal, we examined several dozen fig drupelets from Netiv Hagdud, an early Neolithic village site that lies 1.5 km west of Gilgal. As was the case in Gilgal, more than 90% lacked embryos, and they are therefore considered to be of the same female variety as at Gilgal. Thus, incipient horticulture by humans commenced with the domestication of fig trees in the Levant at about 11,400 calendar years B.P.

Table 1.

Early Neolithic (11,500 to 10,300 years B.P.) fig remains in the Levant.

SiteRegionCalendar years B.P.QuantityView inline
Jericho Phase VIIB (View inline, View inline) Jordan Valley 11,400-10,500 1 + 46
Gilgal I Jordan Valley 11,400-11,200 9 + 313
Gilgal III Jordan Valley 11,700-11,260 1 + 30
Netiv Hagdud (View inline) Jordan Valley 11,300-10,900 1 + 4913
Gesher (View inline, View inline) Jordan Valley 11,300 36
Mureybit Phase III (View inline) Euphrates Valley 11,400-10,600 1 + 3
  • View inline* Bold text, fruit fragments; normal text, drupelets.

  • We define domestication in the context of horticulture as a major positive change in the edibility of a wild nonpalatable fruit brought about by a rare genetic event that would disappear without human intervention. In addition, fig trees, whether parthenocarpic or not, are pre-adapted for relatively easy domestication because the cuttings develop roots more easily than those of any other fruit tree (22). Hence, the reported Gilgal figs, stored together with other vegetal staples such as wild barley (Hordeum spontaneum), wild oat (Avena sterilis), and acorns (Quercus ithaburensis), indicate that the subsistence strategy of these early Neolithic farmers was a mixed exploitation of wild plants and initial fig domestication. Apparently, this kind of economy was widely practiced during the second half of the 12th millennium B.P. throughout the Fertile Crescent (23, 24).

    Supporting Online Material

    www.sciencemag.org/cgi/content/full/312/5778/1372/DC1

    Figs. S1 to S5

    Table S1

    References

    References and Notes

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