https://orcid.org/0000-0002-2951-6508
Abstract
The establishment of European colonies across the world had important demographic consequences because it brought together diverse and distant civilizations for the first time. One clear example of this phenomenon is observed in the Canary Islands. The modern Canarian population is mainly the result of the admixture of natives of North African origin and European colonizers. However, additional migratory flows reached the islands due to the importation of enslaved Africans to cultivate sugarcane and the intense commercial contact with the American continent. In this review, we evaluate how the genetic analysis of indigenous, historical and current populations has provided a glimpse into the Canary Islands’ complex genetic composition. We show that each island subpopulation’s characterization is needed to fully disentangle the demographic history of the Canarian archipelago. Finally, we discuss what research avenues remain to be explored to improve our knowledge of the impact that the European colonization had on its native population.
Introduction
The Canary Islands are located in the Atlantic Ocean, approximately 100 km off the coast of Morocco (Fig. 1). The Canary Islands’ demography is exceptionally complex, involving the migration of people from diverse geographical regions, which have made them an interesting case study for population geneticists. Unlike other archipelagos from Macaronesia, the Canary Islands were inhabited by an indigenous population when rediscovered by Genovese sailors at the end of the 13th century (1). Chroniclers noted that the Canarian natives did not possess the knowledge of navigational methods and had remained isolated from the African continent. Since the first recounts from European chroniclers, the Canarian natives were thought to have a North African origin due to their similarities with Berber populations (2). Archaeological research has also pointed to a Berber origin, based on evidence such as funerary practices or the presence of Libyco-Berber inscriptions (3). Regarding the time of the natives’ colonization of the islands, accelerator mass spectrometry analyses support an initial settlement of the archipelago dating to the beginning of the first-millennium ad (4).
Map showing the location of the Canary Islands (upper panel) and ancestry inference of ancient and current populations of the Canary Islands (lower panel). Left: principal component and unsupervised clustering analyses using the Human Origins dataset (595 710 SNPs) to comparing the indigenous people of the Canary Islands to other ancient and modern populations, modified from Fregel et al. (26). For the principal component analysis (PCA), ancient samples were projected on European, Middle Eastern, North African and sub-Saharan African populations using lsqproject option from smartPCA (39). The unsupervised clustering analysis was performed using ADMIXTURE software (40) and the plot shows average results for relevant populations at K = 8. Right: principal component and unsupervised clustering analyses, comparing the current population of the Canary Islands with their parental populations (98 647 SNPs). To build the dataset, we used data from 1000 Genomes Project (41), Henn et al. (17), Arauna et al. (18), and Guillen-Guio et al. (19). Because different arrays were used to genotype the different datasets, for the PCA, Guillen-Guio et al. samples (genotyped for 71 123 SNPs) were projected on the remaining dataset using lsqproject option from smartPCA (39). The unsupervised clustering analysis was performed using ADMIXTURE software (40) and the plot shows average results for relevant populations at K = 4.
After the first contacts, the islands were deemed of not enough value by explorers due to the lack of gold and silver resources and were only visited to capture natives as slaves (5). This scenario changed when the geostrategic value of the Canary Islands was reconsidered: an archipelago located next to the coast of West Africa would offer an excellent post for providing supplies to expeditions in search of African gold mines and, after the European conquest of America, to ships traveling from Europe to the New World (6). The colonization of the Canary Islands represents one of the first phases of the European expansion in the Atlantic Ocean. The conquest of the Canarian archipelago lasted one century, starting in 1402 when Jean de Bethencourt occupied the island of Lanzarote and ending in 1496 with the defeat of the indigenous people of Tenerife by the Crown of Castile (7). Although some islands received the first European expeditions peacefully, they later suffered revolts due to the enslavement of a large number of their inhabitants (8). The crushing of the resistance resulted in a high mortality rate among the indigenous population (9). Finally, the subsequent admixture with the European colonizers led to an acculturation process of the surviving population, which caused the loss of the indigenous culture and language (10). In addition to the European migratory flow, the import of enslaved Moors and sub-Saharan Africans for the cultivation of sugarcane, and the intense commercial contact with the American continent produced additional admixture with African and Amerindian population sources, creating the multiethnic colonial mosaic that would be the germ of the current Canarian population (11).
In this review, we aim to summarize all the genetic evidence that has been presented to understand the formation of the Canary Islands admixed population and discuss what research avenues remain to be explored to improve our knowledge on the impact of colonialism in its native population.
The Canarian indigenous population
Based on the historical record, current Canarians descend mostly from natives and European colonizers, and to a lesser degree, from enslaved Moors and sub-Saharan Africans, and Latin American migrants. The processes of admixture and acculturation of the indigenous people were complete (11) in such a way that the native population was integrated into the colonial society, and indigenous communities did not persist over time. For that reason, the only way to directly obtain genetic information on the native population is the analysis of ancient DNA (aDNA) from archaeological remains. However, due to the difficulties in obtaining aDNA in warm regions like the Canary Islands, the first genetic evidence on the origin of the indigenous people came from analyzing its current population. Genetic studies using the mitochondrial DNA (mtDNA) and the non-recombinant portion of the Y chromosome (NRY) found a clear North African component on the modern Canary Islands, with a higher contribution observed for the mtDNA (12–14). Regarding the indigenous colonization process, asymmetric distribution of putative North African mtDNA and NRY haplogroups suggested at least two independent waves of settlers from North Africa (13,14), based on the presence of the same genetic background in all islands and specific lineages present only in the islands closer to the continent. Later, autosomal DNA and genome-wide single-nucleotide polymorphism (SNP) analyses (15–19) confirmed the presence of a North African component in the modern population. For example, Botigue et al. (17) found that the current Canarian population has a higher identity-by-descent sharing with North Africans than continental Europe. Regarding the possible geographic origin of the indigenous people, Arauna et al. (18) showed that the North African source in the Canarian population is similar to those on the Atlantic coast.
Although the analysis of the Canary Islands population can provide interesting data, the most appropriate way to characterize the indigenous population is the direct analysis of aDNA from archaeological material. Initially, classical techniques based on the use of the polymerase chain reaction (PCR) were used to analyze both uniparental markers in human remains from different archaeological sites dated from the pre-contact period or identified as belonging to the indigenous culture based on the funerary practices. These studies confirmed the presence of North African mtDNA and NRY lineages in the Canarian indigenous population (20–24). Besides, mtDNA results from four of the seven islands showed high mitochondrial diversity for the islands of Tenerife (20) and La Palma (21), and the partial or complete fixation of specific lineages in La Gomera (23) and El Hierro (24). Different archaeological sites were analyzed in the islands of La Palma and Tenerife, accounting for a total of 30 and 36 samples, respectively. For La Gomera, 52 samples from 10 archaeological sites were analyzed and 65% of the indigenous population belonged to haplogroup U6b1a (60.7% in the northern and 70.8% in the southern region, respectively). For El Hierro, all the individuals analyzed in the Punta Azul site (n = 56) were classified within H1cf haplogroup. This suggested that La Gomera and El Hierro could have experienced stronger genetic drift processes than larger islands with more resources, such as Tenerife. This result is interesting because it implied that the islands’ indigenous colonization was a heterogeneous process and that the different islands could have had different evolutionary histories.
Although the implementation of next-generation sequencing (NGS) techniques has been essential for numerous fields, the research avenues it has opened for aDNA studies have been crucial for the development of the paleogenetics field. The first aDNA study at a whole-genome level was published by Rodriguez-Varela et al. (25). This study included 11 archaeological samples from Tenerife and Gran Canaria, with radiocarbon dates ranging between the 7th and the 11th centuries ce, although enough nuclear data were only recovered for five samples. NGS data confirmed previous evidence pointing to a North African origin for the Canarian indigenous people. This study also provided information on their phenotypic traits, indicating that some of the dominating phenotypes in this population had lactose intolerance, dark hair, light or medium skin color and brown eyes. This dataset was later compared to ancient samples from North Africa (26), concretely from Upper Paleolithic (~15 000 BP), Early Neolithic (~7000 BP) and Late Neolithic sites in Morocco (~5000 BP). This analysis indicated that both Late Neolithic Moroccans and the Canary Islands’ indigenous population were admixed, with an ancient North African component and an early Neolithic European component. Additionally, the Canary Islands’ indigenous people had admixture elements, possibly related to trans-Saharan migrations and the expansion of European Bronze Age populations in North Africa (Fig. 1). As the time for the colonization of the Canary Islands archipelago has been estimated to be between the first-century bc and the first-century ad (27), additional migration waves are expected to have reached North Africa by that time. For example, a European Bronze Age component can be explained by the presence of Bell-Beaker pottery in the North African archaeological record (28,29).
The phylogenetic analysis of 48 ancient mitogenomes from 25 archaeological sites from the seven main islands (27) has shown that most of the mtDNA lineages can be associated with either an autochthonous North African component (haplogroup U6) (30) or with Neolithic expansions in the Near East and Europe (T2 and J2) (31), thus confirming the results obtained with genome-wide data. The presence of putative sub-Saharan African lineages (L1b and L3b1a) (32) and lineages that were frequent in Europe during the Bronze Age (H1e1a and H4a1) (33) support the idea of later migrations in North Africa after the Neolithic period. By comparing samples from the entire archipelago for the first time, it was also possible to confirm that Gran Canaria, Tenerife and La Palma had high genetic diversities, while El Hierro, La Gomera, Fuerteventura and Lanzarote were probably affected by genetic drift and/or bottlenecks (Fig. 2). Differences between the eastern and western islands were also observed, with several mtDNA lineages appearing in higher frequencies in the islands closer to the African continent. This result, coupled with previous archaeological and modern DNA evidence, suggests heterogeneous colonization of the archipelago.
Uniparental markers’ results for indigenous, historical and current Canarian populations. Mitochondrial DNA haplogroup frequencies observed in the indigenous people of the different islands and the whole Canary Islands populations (A), modified from Fregel et al. (27). Note that Lanzarote and Fuerteventura have been considered together as both populations have low sample sizes and, from an archaeological point of view, can be considered the same population due to cultural similarities. Codes are as follows: HIE = El Hierro; PAL = La Palma; GOM = La Gomera; TFE = Tenerife; GCA = Gran Canaria; LAN = Lanzarote; FUE = Fuerteventura; CIP = Whole indigenous population. Mitochondrial DNA (B) and Y-chromosome (C) haplogroup frequencies for the indigenous, historical and current population of the Canary Islands, as well as its main parental populations: the Iberian Peninsula, North Africa and sub-Saharan Africa. Current mitochondrial DNA (D) and Y-chromosome (E) haplogroup frequencies for each island subpopulation and for the whole archipelago. Population frequencies have been obtained from Fregel et al. (22) and Fregel et al. (27). Codes are as follows: CIP = Canarian indigenous population; CON = Canarian historical population; IBE = Iberian Peninsula; NAF = North Africa; SSA = Sub-Saharan Africa. The remaining codes are as before, but corresponding to the current populations of the islands.
The making of the colonial population
Archaeological research on Canarian colonial society has not received as much academic attention as the study of indigenous populations. There are only two historical sites that have been subjected to paleogenetic analyses: La Concepción Church and Finca Clavijo.
La Concepción Church (Santa Cruz de Tenerife, Tenerife) was used as a cemetery during the 18th century. At this time, the port of Santa Cruz was a popular stopping point for ships traveling between Europe and the Americas (11). One of the advantages of using this historical site for characterizing the historical population is that the use of the cemetery had no social restrictions and individuals of various socioeconomic levels were buried there, including enslaved people (34). For that reason, the analysis of the remains deposited at La Concepción Church can provide an approximation to the whole Santa Cruz society at that time. The mtDNA and NRY of the 18th-century population of Tenerife revealed a high genetic diversity (22,35). Although most of the lineages obtained from this cemetery were of European origin (Fig. 2), a high frequency of sub-Saharan African haplogroups was also detected. This result emphasized the importance of the African community in the Canary Islands at this time. In the same vein, the presence of Amerindian lineages highlighted the Canary Islands’ role in the transatlantic contact with the Americas.
The cemetery of Finca Clavijo (Santa María de Guía, Gran Canaria), dated from the 15th–17th centuries, was found near an old sugarcane field. The analysis of the archaeological evidence and the historical sources indicated that Finca Clavijo was the burial site for a marginalized and multiethnic population, most likely related to the slave trade (36). The most striking aspect of the Finca Clavijo site was the presence of non-Christian funerary rituals, implying that it was a multicultural society, tolerant of foreign rituals and syncretism. The analysis of mtDNA at Finca Clavijo revealed that this population had a multiethnic genetic composition (36). Most mtDNA lineages observed at Finca Clavijo are present in northwestern Africa and could be associated with the enslaved Moors’ presence in the islands. Other lineages have an exact sub-Saharan African origin and could be related to enslaved people taken from Senegambia. Surprisingly, the Canarian autochthonous lineage U6b1a was also observed in Finca Clavijo in an individual with teeth modifications usually linked to sub-Saharan Africans. Because this lineage has only been observed in individuals whose ancestry can be traced to the Canary Islands, this result evidenced the enslavement of individuals with indigenous ancestry to work in sugarcane fields.
The current Canarian population
From the genetic point of view, the analysis of the Canarian current population has provided interesting data about the configuration of the colonial society. For example, mtDNA results indicate that current Canarians are a mixture of European, North African and sub-Saharan African lineages, with a reduced Amerindian input (12–14). Genome-wide data have shown that the current population can be modeled mainly by an admixture event between a European and a North African source (Fig. 1), with an estimated date coinciding with the Spanish conquest (18,19). In agreement with historical information, Arauna et al. (18) identified the input of two main components in the Canary Islands using genome-wide data: a European-like source mostly related to the Iberian Peninsula and other one related to a general North African source. The authors also identified an ancestry source related to sub-Saharan Africa and Northwest Europe. As already explained, the existence of a sub-Saharan African component can result from the importation of enslaved Senegambians. On the other hand, the presence of a Northwest European component could be linked to the establishment of Flemish merchants in the islands during colonial times (6).
Admixture estimates using mtDNA and NRY have demonstrated the existence of a sex-biased admixture pattern (12–14,22) (Fig. 3), with a higher North African ancestry for the maternal lineages (~50%) and a higher European ancestry for the paternal ones (~90%). Consequently, genome-wide admixture estimations have produced an intermediate North African contribution (25), ranging between 17 and 31% (depending on the European population chosen for the calculation). This asymmetry is common in admixed populations that underwent processes of conquest and colonization, such as the Canary Islands or Latin America. In these cases, the surviving indigenous population is mostly female due to the high mortality rate of males during the conflict. Also, most of the colonizers are initially male due to the dangerousness and instability associated with the newly conquered territories, and to the dynamics of the Castilian conquering enterprises (6). One striking result has been obtained by comparing the maternal and paternal North African contribution in historical and current populations (22). While the contribution of indigenous maternal lineages only suffered a moderate increase from historical to modern times, the male ones declined from the 18th century to the present (Fig. 3), being progressively replaced by European lineages. This result is consistent with the European conquest and colonization producing an initial sexual asymmetry. However, it suggests that the colonization process produced a progressive displacement of the indigenous male population, most likely influenced by the Europeans’ higher socioeconomic status (22).
Admixture estimations for the historical and current population of the Canary Islands. Top: admixture estimations for the current population obtained using genome-wide SNPs (25), mitochondrial DNA (27) and the Y-chromosome (22). *For the genome-wide SNPs analysis, only two parental populations were considered (indigenous sample gun011 and the Spanish population from Murcia). Bottom: Comparison of mtDNA (left) and NRY (right) admixture estimates for the Canarian historical and current populations (22,27).
Even taking a progressive displacement of the indigenous male population into consideration, estimations of native’s contribution to the current population based on genetic evidence are higher than those obtained by ethnohistorical and demographic studies. It has been estimated that the indigenous people’s population size was 95 000–137 000 before the contact period and was decimated to 7000 in 1504, accounting for a 95–90% of mortality (37). This record led to the belief that the indigenous population was annihilated and that the Canarian population was almost exclusively of European origin. To reconcile this with the genetic estimates, we have to bear in mind that this census only considered whole native families (6), and did not take into account admixed couples, which were mostly composed of indigenous women and European men. Also, discrimination against indigenous families could have played a role in causing individuals to avoid self-identifying themselves as natives. In that sense, the 5–10% value obtained from this census would reflect the acculturation process rather than the survival of the indigenous population.
When the populations of the islands are analyzed independently, differences are observed both regarding their admixture processes and evolutionary history. Current Gomerans have a higher frequency of the mtDNA U6b1a haplogroup, suggesting a high contribution of the indigenous people to the current population (23). However, with this exception, the modern population mtDNA composition is homogeneous across the archipelago (Fig. 2), indicating high human mobility after the European conquest (27). Genome-wide data analysis has shown that the islands of La Gomera and El Hierro contain larger runs of homozygosity than the other islands (19). This result is interesting because the indigenous people of these islands also showed signs of genetic drift and/or inbreeding (23,24), suggesting that the same isolation processes affecting these populations in pre-Hispanic times could have affected them after the conquest. Additionally, those islands that were conquered at the beginning of the conquest (El Hierro, La Gomera, Lanzarote and Fuerteventura) exhibit a larger North African contribution than those with longer conflict periods (La Palma, Tenerife and Gran Canaria) (19). Calculations at an insular level using mtDNA have provided similar differences in the contribution of indigenous lineages to the current population (27), although the island of El Hierro had a lower North African contribution.
One potential problem with admixture calculations, both for uniparental markers and genome-wide SNPs, is the assumption that all North African input is originated by the contribution of the indigenous people. Historical records point to an important influx of enslaved Moors imported as workforce after the conquest, most importantly in Lanzarote and Fuerteventura (38). Although it could be attributed to sampling issues, the sharing of specific mtDNA lineages between the current populations of Lanzarote and Fuerteventura and North Africans (e.g. T2c1d1a1 haplogroup), but not with the indigenous population, could be related to this phenomenon (27). If enslaved Moors significantly contributed to these islands’ colonial population, not considering this input within the North African component can lead to the overestimation of the indigenous contribution to current populations in the eastern islands. However, to perform these analyses, a better understanding of the Canarian indigenous and historical populations and better reference data from North Africa would be needed.
Conclusions
During the last decades, ample ethnohistorical, archaeological, linguistic and genetic evidence has been provided on the origin of the indigenous people of the Canary Islands. Additionally, genetic studies have shed light on the indigenous people’s admixture patterns after the conquest. However, given the complexity of the islands’ demographic history, several other aspects are still unexplored or require further analyses. Regarding paleogenomic analyses, genome-wide data are only available for decontextualized samples from Tenerife and Gran Canaria. Additional spatial and temporal data on the genetic composition of the native people are needed to better understand the indigenous colonization process and the evolution of each island population. For that, genome-wide studies should include samples from all seven islands and from different periods, ranging from the first centuries of the ce to the contact period in the 14th–15th century. Also, a more profound multidisciplinary analysis of the paleogenomic data are needed, comparing archaeological and genetic evidence to understand how demographic and cultural changes correlate.
Regarding the formation of the colonial population, additional historical paleogenomic data are needed to assess how the different parental populations interacted with natives over time. Also, appropriate admixture models are needed to identify the contribution of parental populations that have been experiencing genetic exchanges in both prehistoric and historical times. For example, as most of the colonizers were Spanish and Portuguese, a minor North African contribution reached the islands via Europe, due to the Arab conquest of the Iberian Peninsula in the seventh century. For that reason, admixture modeling using other European populations without historical contact with North Africa could lead to an overestimation of the contribution of indigenous people. Finally, a historical consideration that remains to be explored is the possibility that a portion of the North African contribution of the Canary Islands could result from the introduction of enslaved Moors after the conquest, especially in the islands of Lanzarote and Fuerteventura. With an extensive sampling of ancient, historical and current populations, and more robust admixture models, future research will allow a fine-detailed understanding of the making of the Canarian admixed population.
Acknowledgments
The authors thank the editors for the invitation to participate in this special issue and the reviewers for their helpful comments.
Conflict of Interest statement. None declared.
Funding
R.F. and J.G.S. were funded by a grant (PALEUCOL; PGC2018-094101-A-I00), funded by FEDER/Ministerio de Ciencia e Innovación—Agencia Estatal de Investigación. R.F. and A.C.O. were funded by a grant from Fundación CajaCanarias/La Caixa (GENPAC; 2018PATRI16).
