Genetic history of the population of Sicily

O. RICKARDS, C. MARTINEZ-LABARGA, G. SCANO, G.F. DE STEFANO,1 G. BIONDI,2 M. PACACI,3 AND H. WALTER

Abstract We investigated the genetic heterogeneity of 2354 individuals from the 9 provinces of Sicily. The genetic markers we used were HP, GC, TF, PI, and AKI plus other previously tested polymorphisms, for a total of 24 independent markers. Distinct multivariate statistics were applied to verify the claimed genetic distinctiveness between extant eastern and western Sicilian populations. Our hypothesis stated that any diversity found between the two subpopulations would represent the signature of early colonization of the island by Greek and Phoenician peoples. Correspondence analysis showed that there was no clear geographic clustering within Sicily. The genetic distance matrix used for identifying the main genetic barriers revealed no east-west differences within the island's population, at least at the provincial level. FsT estimates proved that the population subdivision did not affect the pattern of gene frequency variation; this implies that Sicily is effectively one panmictic unit. The bulk of our results confirm the absence of genetic differentiation between eastern and western Sicilians, and thus we reject the hypothesis of the subdivision of an ancient population in two areas.

The making of the indigenous population of Sicily entered its final stages during the early centuries of the first millennium B.C. in the passage from prehistory to recorded history. The first of three waves of colonization to reach Sicily by sea, the Sicani, probably came from northern Africa by way of Spain and later settled the westernmost half of Sicily. In the eighth century B.C. a second mass migration led the Sicels or Siculi, an Indo-European population from the Italian peninsula, to occupy the eastern half of Sicily. The last population to colonize the extreme western area was the Elymians, coming from the Near East, most likely from Anatolia. The marked cultural differentiation that this type of colonization produced between eastern and western Sicily is known to us from archeological excavations and ancient historians, such as Thucydides, Herodotus, and Diodorus Siculus (La Rosa 1989; Moscati 1980, 1987, 1994; Pallottino 1981, 1984; Tusa 1994).

Since the end of the second millennium B.C., Carthaginian or Punic traders, descendants of the Phoenicians in the western Mediterranean, established trading posts along the Sicilian coast. After the Greek invasion during the mid eighth century BsC., they withdrew to the western half of Sicily. The Greeks then rapidly occupied the eastern coast, leaving only the mountainous center in the hands of the increasingly hellenized Siculi and Sicani. The eastwest cultural subdivision of Sicily gradually disappeared with the spread of Latin language and culture imposed by the Romans (third century B.c. to fifth century A.D.), then again under Byzantine (fifth through eighth centuries A.D.) and later under Arab rule (ninth through eleventh centuries). From the Middle Ages onward, Sicily was spared further mass migration to its shores. Whatever cultural subdivision had existed began to fade with time (Finley 1985; Moscati 1980, 1987, 1994; Pallottino 1981, 1984; Tusa 1994).

Once the waves of foreign invaders had ceased, local movements of individuals or small clusters began to characterize Sicily's history. Usually associated with marriage, this short-range migration causes gene flow between local populations. Genes circulated within the same or similar gene pools and consequently led to gradual genetic homogenization of geographically close local units and possible isolation between populations at larger distances. For a better understanding of the phenomena, researchers have sought to answer two questions: (I) Do cultural variability and genetic variability somehow correspond to one another; and (2) are there any traces of the ancient cultural dichotomy in the genetic structure of the present Sicilian population after so long a period of mainly short-distance movements?

For about two decades Cavalli-Sforza and others have related the patterns of some present genetic variations to the spread of ancient populations [summarized by Cavalli-Sforza et al. (1994)]. According to this relation, Piazza et al. (1988), using some classical genetic markers (HLA-A, HLA-B, ABO, Rh, MN, KEL, and HP), seemed to have data suggesting a genetic difference between eastern and western Sicily that could reflect the early pattern of colonization by the Greeks and the Phoenicians. Guglielmino et al. (1991) and Zei et al. (1993) used rare surnames in an effort to validate the hypothesis that the geography of human genes in Sicily maintains the memory of the genetic subdivision of the island following the ancient invasions.

An opposite result was reported by Rickards et al. (1992) and Walter et al. (1997) in their papers based on 10 erythrocyte polymorphisms and GM and KM allotypes. In their studies detailed analysis of the distribution of these markers in all nine Sicilian provinces highlighted a more complex pattern of genetic variability within the Sicilian population than a simple east-west differentiation. Clearly detected in the extant Sicilian gene pool was a clue for more recent gene flow of people from northern Africa and the Middle East superimposed on a predominantly Greek contribution.