*The Olive*

When the oleaster first was tamed and received care marks the beginning of the domestication process. [29, 46] have shown that the wood charcoal kept traces of pruning practices because of specific vessel architecture and shape, as early as 7500 BP in the Portuguese Extremadura. Their results push back by 1,500 years the preceding estimation of olive domestication given in the eastern Mediterranean region.

Recently, Terral's team has revealed that wood charcoal could also reveals traces of watering in the Middle Ages [40]. If the reasons people were pruning the oleaster are unknown, the consequences of pruning probably appeared to these peoples by more regular blossoming over years and more fruits. Today olive cultivars display a wide variability in response to pruning methods that raises questions on the origin of the diversity [15, 47, 48, 49] at the Neolithic C site of Atlit-Yam on the Levantine coast (dated to 7100-6300 yrs. BP, uncalibrated C14) found underwater wells constructed of alternating layers of tree branches and stones, stone-installations, some lined with undressed stones and others dug into the clay sediment. Some of the crushing installations contained thousands of crushed olivestones and waste resulting from the extraction of olive oil. So far this is the oldest known evidence for olive oil extraction.

Origin and History of the Olive 11

periods. All this information lays the foundation required to set up genetic models derived

All molecular data based on several types of methods (isozymes, RAPD, RFLP, ISSR and SSR) have been obtained since 1995 from *Olea europaea* [see 1-4 for review]. Obviously, we neglected reports that established relationships between cultivars unless they are informative in reconstituting the olive's history. Molecular data should be based on samples of wild trees and of cultivars representative of the present genetic diversity. If molecular data are bias in the sampling the conclusion will be probably biased. There is no *a priori*  rational criterion for sampling oleaster and olive cultivar trees due to the ignorance of their origin. Several hundreds of publications have reported data based on different types of molecular markers on various samples of wild trees and cultivars (depending on the country, the easy sampling of wild trees (from the local region or covering several regions)

Evolution of methods is permanent due to progresses in their development. We will not reiterate all methods of studying the history of the olive since the last ice age through domestication, but will try to enable non geneticists to follow our reasoning. The progress in developing molecular markers over the last twenty years has made some techniques lapsed,

Whatever the techniques used to visualize the genetic diversity, the main feature is to aggregate data from the three DNA supports in the olive tree: the mitochondrial DNA (mt, ), the Chloroplast DNA (cp, [58] and the nuclear DNA (nu-, [15, 59, 60, 61]. The information brought by the three compartments is not proportional to the length of the DNA, but by the mode of inheritance and by their mode of evolution. The mt-DNA is maternally inherited as the cp-DNA [62], and evolves by recombination and by mutation and deletion, respectively. These DNA pools are constituted from several copies of the same molecule (they are haploid) and define 'haplotype'. The nuclear DNA is made of two halves from each parent. If the two alleles at one locus are discernible they are said to be codominant, and if only one is discernible due to the other one being absent then the discernible allele is dominant over the hinted allele. If the same dominant allele is found in two different individuals they are said to be similar, whereas if the same two alleles are found in two different individuals

Population genetic methods based on similarities (established for dominant alleles) compares at each locus two heterogeneous groups, one homogenous (the double recessive) and one heterogeneous (the double dominant and the heterozygous). All methods used to structure the genetic diversity are based on the allelic frequencies that are firm with co-

from the present genetic diversity recorded in the oleaster and in olive cultivars.

**Mediterranean basin** 

and with different methods to analyze data.

they are said to be identical.

*Evolution of methods to get and to analyze molecular data* 

although they have released plenty of information [4, 57].

**6. Molecular data enabling genetic inference for subsp. europaea in** 

Remains that enabled us to trace the olive tree are more and more numerous from the Mesolithic to the Historical periods. The most informative remains are olive endocarps (stones) that are frequently found in fireplaces (they are charred or carbonized). Terral's team has developed morphometric methods that appeared efficient in analyzing such remains [50]. The main features that result from their analyses are based on the fact that the morphometry of the endocarps has change during the domestication process. Using modern and ancient reference samples they screened and pointed out domesticated remains and unraveled some cultivar relationships. If many stones together in an archaeological site can reveal some transition phase between the wild to the domesticated olive (many broken stones together probably represent oil processing), numerous remains are single or a few stones and consequently these methods are limited on such samples. The accumulation of a few stones probably represents eating olives. However, secondary usage of olive pressing wastes may limit finding traces of olive oil production based on olive remains alone [51].

Pottery types absorb indications of the type of fat they have stored. Pottery types devoted to olive oil as containers for perfumes are aryballos and alabasters, which are widely present throughout the Mediterranean basin due to their diffusion by Greek and Roman cultures [52]. Ceramic chronologies are strict and factories are well recorded, providing a large corpus of data on exchange and trade during the historic periods. Documentation indicates that people used several plant oils (at least flax, saffron, safflower, castor oil and poppy), however, it is possible to differentiate plant oils from animal fats and to identify plant oils by the fatty acid composition obtained from pottery remains [53, 54, 55, 56].

Remains are concrete and their preservation is of importance for future diagnostic methods. The materials from sites studied by all the authors will probably tell more in the future. Furthermore, archaeology continues to uncover new sites and materials and this is likely to continue especially for the southern and eastern parts of the Mediterranean coasts.

In conclusion, the archaeological materials have enabled researchers from different disciplines to anchor the wild and cultivated olive in regions where they naturally thrived and colonized, respectively. Moreover, biologists and archaeologists have defined the basic elicit statistical differences between the wild and the cultivated olive for key historical periods. All this information lays the foundation required to set up genetic models derived from the present genetic diversity recorded in the oleaster and in olive cultivars.
