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Brief communication Coexistence of two distinct patterns in the surname structure of Sicily.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 120:195–199 (2003)
Brief Communication: Coexistence of Two Distinct
Patterns in the Surname Structure of Sicily
Angelo Pavesi,1* Paola Pizzetti,1 Enzo Siri,2 Enzo Lucchetti,1 and Franco Conterio1
1
2
Department of Evolutionary and Functional Biology, University of Parma, I-43100 Parma, Italy
Department of Environmental Sciences, University of Parma, I-43100 Parma, Italy
KEY WORDS
human population; surnames; migration rate; population sampling;
multidimensional scaling
ABSTRACT
The extent of variation in the migratory
movements that occurred in Sicily was evaluated using
surname data taken from the telephone directories of the
390 communes of the island. The surname distribution of
each commune was linearized by a log-log transformation,
and a significant fit to a linear regression model was found
in almost all cases. Interestingly, the slope of the regression line appeared to be a sensitive indicator of the different level of isolation associated with each Sicilian commune. By this approach, two distinct groups of communes,
showing a higher or lower degree of isolation, were obtained, and two independent analyses of the surname
structure of Sicily were carried out. A first multidimensional scaling analysis, based on the more isolated com-
munes, yielded evidence for a more ancient pattern, characterized by a geographical gradient along the east-west
axis. The same analysis, addressed to the less isolated
communes, instead highlighted a wide network of interactions between geographically distant zones of the island. The fitting of the surname distribution to the log-log
model allowed for the detection of a narrow subset of 35
Sicilian communes, whose significantly higher degree of
isolation was statistically proved by the parallelism test.
We believe that a genetic analysis focused on such specific
zones of the island could reveal ancient patterns of differentiation, thus helping to answer the controversial question of the genetic history of Sicily. Am J Phys Anthropol
120:195–199, 2003. © 2003 Wiley-Liss, Inc.
Sicily is the largest island in the Mediterranean
Sea, and for a long time it was the meeting point of
ancient civilizations. The complex historical events
that occurred in the past are likely stored in the
genetic pool of the present-day Sicilian population.
However, independent studies of the genetic structure of the island have led to controversial results.
Based on autosomal markers such as blood group or
human leucocyte antigen (HLA) loci, Piazza et al.
(1988) highlighted a genetic distinctiveness of east
Sicily, which was explained as the result of a consistent introduction of genetic variants during
Greek colonization (eighth century BC). On the contrary, further studies on the geographical distribution of other genetic systems did not support the
view of a west-east difference within island’s population (Rickards et al., 1992; Walter et al., 1997).
The lack of a clear genetic gradient was explained as
an effect of a long period of short-range migrations,
beginning from the Middle Ages onward and causing
gene flow between local populations (Rickards et al.,
1998).
Surnames, whose transmission from father to
children is roughly similar to that of genetic traits,
have also been used to describe the population structure of Sicily. Guglielmino et al. (1991) analyzed the
distribution of surnames taken from consanguineous marriages, and pointed out a gradient in the
west-east axis of the island. A serious limitation of
this approach lies in the fact that surnames are an
inadequate marker to reconstruct ancient demographic events, because their use in Italy was institutionalized only at the end of the sixteenth century.
However, analyses of surname data, which are easier and less expensive to collect than data from
genes, can offer insights into microevolutionary processes acting on human populations, such as genetic
drift and migration (Allen, 1988; Piazza et al., 1987).
According to this view, and based on the vast number of surnames from telephone guides, RodriguezLarralde et al. (1994) estimated the degree of microdifferentiation within each Sicilian province, and
pointed out that geographic distance has an important effect on surname variation in Sicily.
©
2003 WILEY-LISS, INC.
Grant sponsor: National Research Council of Italy; Grant number:
CNR 99.3801.PF36.
*Correspondence to: Angelo Pavesi, Department of Evolutionary
and Functional Biology, University of Parma, Parco Area delle Scienze 11/A, I-43100 Parma, Italy.
E-mail: angelo.pavesi@unipr.it
Received 28 may 2001; accepted 18 February 2002.
DOI 10.1002/ajpa.10120
Published online in Wiley InterScience (www.interscience.wiley.
com).
196
A. PAVESI ET AL.
In the present work, we reanalyzed the surname
data from Sicily, using an updated list of telephone
users, with the aim of more accurately appreciating
the extent of variation in the migration phenomenona that occurred within the island’s population.
On the basis of a nonstandard statistical approach,
the shape of the distribution of surnames was used
as a sensitive indicator of the different level of isolation associated with each Sicilian commune. This
information made possible a finer elucidation of the
complex pattern of surname relationships between
the various subregions of the island, which could
explain the divergent conclusions previously obtained by the genetic polymorphism distributions.
The surnames of all individual Sicilian subscribers, updated to 1994 and filtered by removing commercial customers, were extracted from the computerized records of the Italian Telephone Company
(813,364 records accounting for 1,592,798 users with
79,717 different surnames). A list including the frequency of different surnames was obtained for each
of the 390 communes. After the exclusion of the
eight communes located on the minor islets, a total
of 382 localities was analyzed with the log-log transformation model (Fox and Lasker, 1983; Barrai et
al., 1989), which linearized the frequency of surnames over their occurrence. With this method, the
surname structure of each Sicilian commune was
described by a, the intercept of the regression line on
the y axis, and b, the slope of the regression line
(goodness of fit was tested by variance analysis).
Sixteen communes, having an extremely low population density and showing a surname distribution
poorly fitting the regression model, were not considered. The exclusion of a larger set of 54 communes
was based on the fact that it contains large or industrial towns, whose surname structure is deeply
affected by massive immigration from a wide surrounding area.
Our interest was thus devoted to the 312 remaining communes which exhibited a significant fit to the
regression model in almost all cases (311 communes). A first analysis, based on the Spearman
rank coefficient, revealed a strong correlation (rs ⫽
0.98) between parameter a and the number of surnames (S) found in a given commune, a quantity
which, in turn, appeared to be associated with the
total number of telephone users (N) in that commune (rs ⫽ 0.94). No correlation was found, in contrast, between parameter b and the number of surnames (rs ⫽ ⫺0.03), indicating that the range of
variation of the regression slope is largely independent of the size of the population.
Interestingly, parameter b appeared to be a valuable tool for estimating the extent of variation between the surname structures of the Sicilian communes under examination. This notion was
suggested by a visual inspection of the surname
distribution from the two communes with the highest (⫺0.46) and the lowest value (⫺1.83) of the regression slope. Geraci Siculo (b ⫽ ⫺0.46; see Fig. 1A)
is a mountain village located in the High Madonie
region of the province of Palermo. Its surname structure was characterized by a relatively low number of
surnames represented only once (64 rare surnames)
and a proportionally high number of the most frequent ones (28 surnames with a range of redundancy from 9 –32). These features, combined with a
rather homogeneous surname structure (743 telephone subscribers with only 157 different surnames), supported the hypothesis that Geraci Siculo
experienced a long history of marked isolation.
Sant’Alessio Siculo (b ⫽ ⫺1.83; see Fig. 1B) is a
small town situated on the Mediterranean coast of
the province of Messina. Compared to Geraci, it
showed a strong increase in rare surnames (288
surnames occurring once) and a lower amount of the
most abundant ones (7 surnames with a range of
redundancy from 9 –32). Since a high frequency of
unique surnames is presumably due to recent immigration, the heterogeneous structure of Sant’Alessio
(a total of 419 different surnames for 745 telephone
subscribers) can be viewed as the result of shortrange migrations of individuals, leading to a consistent gene exchange between local populations.
These observations suggest that increasing values
of parameter b should reflect a gradual increase in
the level of isolation in the 311 Sicilian communes
under examination. By choosing the median value of
b (⫺1.02) as threshold, two large groups of communes, each containing 155 entities, were obtained,
and two independent analyses of the surname structure of Sicily were then carried out. Though surnames are relatively recent population markers, it is
probable that cultural or genetic differences existing
before the surname diffusion could persist in those
communes with a b value above the median, since
they include the more isolated localities of Sicily.
The effects of isolation by distance should be extremely weak when considering the alternative set
of communes (b below the median value), whose
surname distribution suggests recent events of population admixture. If this premise is correct, we
would obtain two different pictures of the population
structure of Sicily, depending on the set of communes under examination.
As shown in Figure 2, the entire island was divided into 12 geographical regions. Provinces showing a large extension along the latitudinal or longitudinal axes were subdivided into a western and an
eastern part (Palermo, Messina, and Agrigento) or a
northern and a southern part (Catania). A joined
area was obtained from the two small provinces
situated in the extreme south corner of Sicily, i.e.,
Siracusa and Ragusa. The three remaining regions
correspond to the provinces of Trapani, Caltanissetta, and Enna. Using the two groups of communes
selected above, two distinct collections of surnames
were obtained for each of the 12 regions (Table 1).
The relationships between surname frequencies of
these regions were evaluated by the correlation coefficient R (Chen and Cavalli-Sforza, 1983). Two dis-
SURNAME STRUCTURE OF SICILY
197
Fig. 1. Log-log surname distribution and linear regression analysis of the two Sicilian communes showing the highest (Geraci
Siculo, A) and lowest (Sant’Alessio Siculo, B) value of parameter b, the slope of the regression line.
Fig. 2.
Sicily.
Twelve areas used to investigate surname structure of
tinct matrices of similarity were obtained, and some
differences between them were apparent at a preliminary inspection. Referring to the matrix based
on the more isolated communes, the extreme southern region of Sicily (Siracusa and Ragusa) showed a
significant correlation with the southern part of Catania (R ⫽ 0.43), but a low correlation with all the
remaining regions (R values from 0.21– 0.29). The
alternative matrix, conversely, revealed a good correlation of Siracusa and Ragusa not only with south
Catania (R ⫽ 0.41) but also with more distant zones
of Sicily, such as north Catania (R ⫽ 0.44), east
Messina (R ⫽ 0.35), Enna (R ⫽ 0.36), and west
Palermo (R ⫽ 0.35). This latter result could be due to
the migration of individuals or small groups from
the extreme south of the island to northeast Sicily,
probably along the coast, or to northwest Sicily
through the interior.
It is interesting to note that different patterns of
migration were also inferred by analyzing the province of Enna, located in the heart of Sicily. A strong
isolation was apparent from an inspection of the
first matrix, since Enna showed a low degree of
correlation even with the nearest provinces, such as
Caltanissetta (R ⫽ 0.31) or south Catania (R ⫽
0.30). Examination of the alternative matrix instead
suggested a large network of interactions with western and eastern regions. In fact, Enna exhibited a
good correlation with the two areas of Palermo (0.43
and 0.36) as well as all five regions in the eastern
half of Sicily (R values ranging from 0.35– 0.48).
A dual graphic representation of the surname
structure of Sicily was then obtained with the non-
198
A. PAVESI ET AL.
TABLE 1. Number of different surnames and total number of telephone users in 12 regions of Sicily, as obtained from communes
with a higher (1) or lower (2) degree of isolation1
1
Trapani
West Palermo
East Palermo
West Agrigento
East Agrigento
Caltanissetta
Enna
West Messina
East Messina
North Catania
South Catania
Siracusa-Ragusa
Total
1
2
Number of
communes
S
9
19
18
15
14
15
6
17
16
7
7
12
155
4,608
5,235
2,571
3,074
2,962
2,595
2,028
2,568
2,458
2,238
4,072
4,579
38,988
N
Number of
communes
S
N
40,549
43,688
20,267
27,716
29,853
21,366
13,677
16,348
15,343
14,582
32,359
43,150
318,898
7
21
10
3
3
2
11
18
39
24
7
10
155
1,653
5,139
4,375
1,086
1,526
926
4,449
4,365
6,850
9,389
2,057
5,353
47,168
10,033
31,798
26,779
5,320
6,512
3,906
30,663
27,410
47,570
74,935
10,430
34,101
309,457
S, surnames; N, total number of telephone users.
metric multidimensional scaling (NMDS) technique
(Kruskall, 1964). A first NMDS analysis, which focused on the distance matrix based on the more
isolated communes, yielded a map in which four
clusters are easily recognizable (Fig. 3A). Each cluster is formed by contiguous regions, forming a southeastern cluster (Catania, Enna, and Siracusa-Ragusa), a northeastern cluster (Messina), a western
cluster (Trapani, Palermo, and west Agrigento), and
a southern cluster (east Agrigento and Caltanissetta). The main division provided by the projection
of points on the first axis of the map was along an
east-west direction, as pointed out by a significant
correlation between coordinates on axis 1 and coordinates along the geographical latitudinal axis (rs ⫽
⫺0.75). A partial deviation from this pattern was
found for Trapani and west Palermo, which were
placed in close proximity to the center of the map.
Such a position, weakly concordant with a geographical location at the extreme west of Sicily, was ascribed to a relatively high degree of correlation with
south Catania (R ⫽ 0.36 for west Palermo; R ⫽ 0.37
for Trapani), which was only slightly lower than
those with the surrounding regions.
A different pattern of the surname structure of
Sicily was provided by NMDS analysis of the distance matrix based on the less isolated communes.
In this case, 8 of the 12 regions, albeit geographically distant, tended to form a cluster at the center
of the map (Fig. 3B). The close relatedness of most of
the regions on axis 1 of the map suggested longrange migratory movements involving the largest
provinces of Sicily (Palermo, Messina, and Catania),
as well as the extreme southern region (SiracusaRagusa) and the interior region (Enna). On the same
axis, the different position of the two areas of the
province of Agrigento was explained as the result of
short-range migrations in western and eastern directions, respectively. In accordance with these observations, the correlation between coordinates on
axis 1 and coordinates along the geographical latitudinal axis was statistically nonsignificant (rs ⫽
0.20).
Fig. 3. Multidimensional scaling analysis of surname relationships between 12 areas of Sicily. A: Graphic map based on 155
more isolated communes. B: Graphic map based on 155 less
isolated communes.
Rather than a general outline of the surname
structure of Sicily (Rodriguez-Larralde et al., 1994),
these results highlight the coexistence of an ancient
SURNAME STRUCTURE OF SICILY
substrate, characterized by a major east-west gradient, together with a more recent one, indicative of a
dense network of contacts between local populations. Obviously, even a rough dating of the demographic processes associated with the more ancient
substrate is a problematic task. As mentioned above,
surnames are relatively young markers, and their
distribution often reflects cultural variations,
which are transmitted partly vertically, and partly
horizontally (Cavalli-Sforza and Feldman, 1981).
Though the cultural dichotomy between east and
west Sicily, still evident today in many respects, had
its origins during prehistoric times (Tusa, 2000),
the hypothesis of a corresponding genetic differentiation should be tested by an accurate population sampling based on highly polymorphic genetic
markers.
The last aspect of our study yielded valuable information about the criterion to be followed for the
collection of population samples in Sicily. By using
the parallelism test (test of equality of the regression coefficiens), the slopes of the regression line
within the group of the more isolated communes
were compared with each other, and a narrow subset
of 35 localities with a significantly higher degree of
isolation was selected (data not shown). The deep
isolation of these communes, evenly distributed
across the island, was further supported by the fact
that surnames represented only once covered a low
fraction (about 10%) of the total amount of subscribers, whereas the 20 most frequent surnames accounted for a fraction often above 50%. Based on
classic markers (e.g., blood groups) or molecular
polymorphisms at the DNA level, a genetic analysis
focused on such specific zones of the island should at
least reveal geographic patterns of differentiation,
thus helping answer the controversial question of
the genetic history of Sicily.
199
ACKNOWLEDGMENTS
We are grateful to the Italian Telephone Company
(SEAT) for allowing us to use their computerized
records listing the surnames of their customers. The
critical comments of the anonymous referees are
also gratefully acknowledged.
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