3. Discussion
Prior to this comparison, to treat the samples as a single population or three independent groups, AMOVA and STRUCTURE analysis were performed. A comprehensive geographical coverage of the three current provinces was performed to select the samples included in this study, comprising both coastal and inland towns as far as a proportional distribution of samples from the capital cities of the provinces. No subdivisions were seen in terms of the geographical origin of the samples, as evidenced by the STRUCTURE analysis. Samples could not be grouped into more than one cluster, and few variations between populations were observed by AMOVA. This finding is consistent with historical and sociocultural expectations based on the shared origin of these populations with regard to their geographical proximity.
In the first level of the comparison, based on the allele frequencies, the GMA population fell within the Spanish populations (
Figure 1). In addition, the population from Basque Country lay farther from the rest of the Spanish population due to the differences between the D13S317 (allele 8), TPOX (allele 12), and TH01 markers (allele 9.3); data in
Supplementary Table S6. The use of a large number of SNPs confirms that Basques are differentiated from other European populations (
Rodríguez-Ezpeleta et al. 2010), confirming its position in the correlation analysis.
Similar results were obtained in the study of genetic distances by MDS. Two clusters were observed, coinciding with the geographical distribution of the populations. Dimension 1 clearly separated the North African from Spanish populations. The GMA population clustered with other Spanish populations (
Figure 2).
Based on the study of the 15 autosomal STRs, in the distance analysis, the North African populations had little influence on the GMA population (
Figure 2), not higher than in other Iberian Peninsula populations. It is difficult to fathom that few African components survived despite 700 years of occupation. The similarity between the GMA and European populations—specifically, the Spanish populations—rendered the identification of the differences between them difficult. Further, the STRUCTURE analyses confirmed these results (
Figure 3). The similarity might be attributed to the lack of genetic interaction between the Muslim population that inhabited the territory and the Spanish conquerors. Historical data indicate that the Muslim people who inhabited the Kingdom of Granada were expelled or isolated and that few were Christianized and remained in the region. In addition, after occupation of the city of Granada by the Spaniards in 1492, people were taken from the north to inhabit the region, thus isolating the Muslims further. These data are supported by the results on the origin of the surnames of the individuals, wherein the surnames that originated in the north or center of Spain are more common today in the south.
North African ancestry in Europe and, in particular, in the Iberian Peninsula has been broadly studied. Genome-wide SNP data from over 2000 North African and European individuals show that recent North African ancestry is highest in Southwestern Europe, with levels rising to 20% (
Botigué et al. 2013). Studies based on autosomal single nucleotide polymorphisms in populations of the Iberian Peninsula show that North African ancestry does not reflect proximity to North Africa or even regions under more extended Muslim control; the highest amounts of North African ancestry found within Iberia are in the west (
Bycroft et al. 2019), supporting previous studies based on Y chromosome binary markers. These studies determined that the Islamic rule of Spain left only a minor contribution to the current Iberian Y chromosome pool (
Bosch et al. 2001), such that the highest proportions of North African ancestry are found in Galicia and Northwest Castile (
Adams et al. 2008). Similar results have been observed in a detailed analysis of Y chromosome STR markers in the same population (
Saiz et al. 2019). In addition, recent mitochondrial DNA analysis based on 7611 control region sequences revealed that typical sub-Saharan and North African lineages are slightly more prevalent in South Iberia, although at low frequencies (
Barral-Arca et al. 2016).
Furthermore, genomic data from 45 individuals dated between the 3rd and the 16th centuries reveal that current populations from the south of the Iberian Peninsula hold less North African ancestry than the ancient Muslim burials, reflecting the expulsion of Moriscos and repopulation from the north (
Olalde et al. 2019).
Even though the microsatellites used in this study were selected for forensic studies because of their high degree of variation within populations, their levels of interpopulation variation are relatively low but sufficient to assess recent genetic relationships between populations. This makes them a useful tool in population genetic studies based on migratory movements that occurred in the last centuries (
Gaibar et al. 2012;
Dahbi et al. 2023). However, studies with other lineage polymorphisms, such as mitochondrial DNA or Y chromosome polymorphisms, are necessary to fully support the results obtained with autosomal markers.
In Spain, the use of surnames became widespread among the Christian population in the 10th century but did not expand throughout the population until the 12th century. However, until the Council of Trent (1545–1563), informal and lax rules on surnames were established. The introduction of surnames during the Middle Ages coincides with the reconquest of the territory that was under Muslim rule.
The wide range of surnames in the GMA samples is supported by the history of this region. Historical data indicate that the Moors who inhabited the Kingdom of Granada were expelled and isolated. Few of them converted to Christianity and remained in the region; those who did were known as new Christians. During this period, Muslims and Jews adopted Christian surnames, as well as the male inheritance system of these names. Later, after the occupation of the city of Granada by the Spaniards in 1492, the Moors were relegated to the zone of the Alpujarra until 1570, from where they were expelled. All of these regions were repopulated with people from the north and center of the Peninsula. There was no contact between new Christians and old Christians. In 1609, all Moors and new Christians were expelled from the Iberian Peninsula to North Africa.
The tremendous isolation of the Moriscos and the little contact between them and the new settlers are reflected in our results on surnames. These patterns explain how most surnames had a Castilian or Galician origin, whereas most surnames had higher frequencies in Southern Spain. A total of 12.57% of surnames with the highest number of individuals who were born in the south of the Peninsula were Galician, Asturian, or Cantabrian in origin (
Figure 5b). Among them, there are such names as Carmona, Cubero, Ferrón, Montes, Padial, Rojas, and Santiago; i.e., nowadays surname Padial is mostly represented in the province of Granada, 11.04%, but it has no representation in Galicia. Conversely, 18.03% of surnames with the highest number of individuals who were born in the south of the Peninsula came from the center of the Peninsula, Castilla León, and Castilla la Mancha, such as Burgos, Castillo, Domínguez, Guerrero, León, and Romero (
Figure 5b). Finally, 7.65% of surnames with the highest number of individuals who were born in the south of the Peninsula were Navarrese–Aragonese in origin—e.g., Aragon, Cortés, Navas, and Soto (
Figure 5b). Although many languages have historically been spoken in the Iberian Peninsula—Castilian, Portuguese, Galician, Basque, Catalan, Arabic, and Hebrew, giving rise to certain characteristic surnames—most of the Spanish population has surnames of Castilian–Leones origin, which predominate the entire Spanish province (
Calderón et al. 2015).
5. Conclusions
The former Kingdom of Granada comprised the current territories of Granada, Málaga, and Almería, behaving as a whole population in regard to its genetic structure.
The analysis of genetic information with regard to the surnames indicated that the expulsion of the inhabitants of the former Kingdom of Granada and the repopulation of the region were so thorough that it was difficult to note any significant traces of the genetic legacy of the former inhabitants when compared to the genetic North African influence found in the rest of the populations of the Iberian Peninsula.
Autosomal STRs have been widely used in molecular anthropology as an informative ancestry tool for reconstructing human expansion, hel** to understand the evolutive history of human populations, and to assess population origins, migrations, and miscegenation. The results of this study illustrate how interdisciplinary collaboration among forensic DNA ty** tools such as autosomal STR ty**, population genetics analysis, and onomastics may be useful to understand how populations have evolved, sometimes even illuminating obscure episodes in history.