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"Zohary, Daniel"
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Unconscious Selection and the Evolution of Domesticated Plants
Two types of selection operate (and complement each other) in plants under domestication: (a) conscious or intentional selection applied by the growers for traits of interest to them; (b) unconscious or automatic selection brought about by the fact that the plants concerned were taken from their original wild habitats and placed in new (and usually very different) human-made or human-managed environments. The shift in the ecology led automatically to drastic changes in selection pressures. Numerous adaptations vital for survival in the wild environments lost their fitness under the new sets of conditions. New traits were automatically selected, resulting in the build-up of characteristic “domestication syndromes,” each fitting the specific agricultural environment provided by the farmer. The present paper assesses the evolutionary consequences of the introduction of the wild plants into several sets of contrasting farming situations. These include: (a) the type of maintenance applied, whether seed planting or vegetative propagation; (b) the plant organs for which the crop has been grown, whether they are reproductive parts or vegetative parts; (c) the impact of the system of tilling, sowing, and reaping on the evolution of grain crops; (d) the impact of the horticultural environment on fruit crops.
Journal Article
The Neolithic Southwest Asian Founder Crops
This article reviews the available information on the founder grain crops (einkorn wheat, emmer wheat, barley, lentil, pea, chickpea, and flax) that started agriculture in Southwest Asia during the Pre-Pottery Neolithic period, some 11,000–10,000 years ago. It provides a critical assessment for recognizing domestication traits by focusing on two fields of study: biology and archaeobotany. The data in these fields have increased considerably during the past decade, and new research techniques have added much to our knowledge of progenitor plants and their domesticated derivatives. This article presents the current and accumulated knowledge regarding each plant and illustrates the new picture that emerged on the origin of agriculture.
Journal Article
The Neolithic Southwest Asian Founder Crops
This article reviews the available information on the founder grain crops (einkorn wheat, emmer wheat, barley, lentil, pea, chickpea, and flax) that started agriculture in Southwest Asia during the Pre-Pottery Neolithic period, some 11,000-10,000 years ago. It provides a critical assessment for recognizing domestication traits by focusing on two fields of study: biology and archaeobotany. The data in these fields have increased considerably during the past decade, and new research techniques have added much to our knowledge of progenitor plants and their domesticated derivatives. This article presents the current and accumulated knowledge regarding each plant and illustrates the new picture that emerged on the origin of agriculture.
Journal Article
Monophyletic vs. polyphyletic origin of the crops on which agriculture was founded in the Near East
The following comparisons between crops and their closely related wild relatives provide clues for discriminating between monophyletic and polyphyletic origins under domestication: (i) Presence or absence of patterns indicative of founder effects in the cultivated genepool, compared to the amount of variation present in its wild progenitor. (ii) Uniformity or lack of uniformity (within a crop) in genes governing principal domestication traits (traits that were automatically selected for once the wild progenitor was introduced into cultivation). (iii) Species diversity: The number of closely related (congeneric) wild species with similar potential for domestication, native to the area under consideration; and how many of them entered cultivation. The present paper evaluates the information available on the eight crops that founded Neolithic agriculture in the Near East; and arrives at the conclusion that emmer wheat Triticum turgidum L. subsp. dicoccum Schúbler, einkorn wheat T. monococcum L., pea Pisum sativum L., and lentil Lens culinaris Medik. were very likely taken into cultivation only once or – at most – a very few times. Also chickpea Cicer arietinum L., bitter vetch Vicia ervilia (L.) Willd., and flax Linum usitatissimum L. seem to have been domesticated in a similar way, but the evidence concerning them is much scarcer. Only for barley Hordeum vulgare L. are there indications that it has been domesticated more than once – but again only a very few times.
Journal Article
Beginnings of Fruit Growing in the Old World
The article reviews the available information on the start of fruit tree cultivation in the Old World. On the basis of (i) evaluation of the available archeological remains and (ii) examination of the wild relatives of the cultivated crops, it was concluded that olive, grape, date, and fig were the first important horticultural additions to the Mediterranean grain agriculture. They were most likely domesticated in the Near East in protohistoric time (fourth and third millennia B.C.) and they emerge as important food elements in the early Bronze Age. Domestication of all four fruit trees was based on a shift from sexual reproduction (in the wild) to vegetative propagation of clones (under domestication). Olive, grape, date, and fig can be vegetatively propagated by simple techniques (cuttings, basal knobs, suckers) and were thus preadapted for domestication early in the development of agriculture. The shift to clonal propagation placed serious limitations on selection and on fruit set under cultivation. We have examined the consequences of this shift in terms of the genetic makeup of the cultivars and traced the various countermeasures that evolved to ensure fruit set. Finally, it was pointed out that in each of these classic fruit trees we are confronted with a variable complex of genuinely wild types, secondary weedy derivatives and feral plants, and groups of the domesticated clones, which are all interfertile and interconnected by occasional hybridization. It was concluded that introgression from the diversified wild gene pool facilitated the rapid buildup of variation in the domesticated crops.
Journal Article
Distribution of Wild Wheats and Barley
If we accept the evidence at face value, we are led to conclude that emmer was probably domesticated in the upper Jordan watershed and that einkorn was domesticated in southeast Turkey. Barley could have been domesticated almost anywhere within the arc bordering the fertile crescent. All three cereals may well have been harvested in the wild state throughout their regions of adaptation long before actual farming began. The primary habitats for barley, however, are not the same as those for the wheats. Wild barley is more xerophytic and extends farther downslope and into the steppes and deserts along the wadis. It seems likely that, while all three early cereals were domesticated within an are flanking the fertile crescent, each was domesticated in a different subregion of the zone. Lest anyone should be led to think the problem is solved, we wish to close with a caveat. Domestication may not have taken place where the wild cereals were most abundant. Why should anyone cultivate a cereal where natural stands are as dense as a cultivated field? If wild cereal grasses can be harvested in unlimited quantities, why should anyone bother to till the soil and plant the seed? We suspect that we shall find, when the full story is unfolded, that here and there harvesting of wild cereals lingered on long after some people had learned to farm, and that farming itself may have orig inated in areas adjacent to, rather than in, the regions of greatest abundance of wild cereals. We need far more specific information on the climate during incipient domestication and many more carefully conducted excavations of sites in the appropriate time range. The problem is far from solved, but some knowledge of the present distribution of the wild forms should be helpful.
Journal Article
Genetic variability in sexually dimorphic and monomorphic populations of Populus euphratica (Salicaceae)
The genetic polymorphism of three populations of the dioecious riparian tree Populus euphratica Oliv. In Israel was examined with isozyme tests. Twelve enzyme systems revealed 20 putative loci, of which 13 were polymorphic. A centrally located population (comprising both females and males) was sampled, as well as two small peripheral and isolated stands: one comprised of only females and one containing males only. Genetic diversity values in P. euphratica were usually lower than those reported in other poplars and other species with similar life-history traits. The highest genetic diversity was found in the central, sexually dimorphic population; however, the sexually monomorphic (unisexual) marginal populations also manifested some genetic diversity, with the lowest values in the male population. Each of the unisexual populations could have originated from very few founder individuals of the same gender. The genetic variability detected in the unisexual populations may reflect somatic mutations accumulated in a vegetatively reproducing lineage over a long time span.
Journal Article
Pulse domestication and cereal domestication: how different are they?
Evidence is brought to indicate that the domestication of lentil and pea is not very different from that of wheat and barley. All these Near East crops are characterized by basically the same domestication traits the key elements of which are breakdown of the wild mode of seed dispersal and loss of germination regulation. It is argued that both in the pulses and in the cereals these traits evolved in the same way. The changes are best explained by assuming that mutations causing the loss of the wild-type adaptations were automatically selected for soon after people transferred the wild progenitors into a system of planting and reaping.
Journal Article
Patterns of isozyme diversity and vegetative reproduction of willows in Israel
Isozyme tests were used to examine the genetic structure of six populations (
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individuals) of the two willow species in Israel,Salix albaandSalix acmophylla. The 14 enzymes revealed 23 putative loci, of which 15 were polymorphic. Sexually dimorphic populations (females and males) and monomorphic ones (all female) were tested in these two species, with the following results: (1) The two sexually dimorphicS. albapopulations were the most variable in isozymes. (2) The all‐female population of this species had lower genetic diversity. The three testedS. albapopulations are part ofS. alba's continuous geographical distribution in the Upper Jordan Valley in Israel. Apparently, genetic variability is maintained in this area and, to some degree, also in the all‐female stand. (3) However, the sexually dimorphicS. acmophyllapopulation showed lower isozyme diversity than theS. albapopulations, probably becauseS. acmophyllapopulations in Israel tend to be smaller and more isolated than those ofS. alba. (4) The two all‐female populations ofS. acmophyllashowed no variability at all; i.e., all 23 loci were monomorphic, indicating that each of these two populations are a single clone. The biased sex ratios, together with the relatively low values of genetic diversity and heterozygosity indicate a possible genetic drift, strong sib‐mating, and vegetative propagation in these willow populations.
Journal Article