Genetic and demographical analysis of San Pietro Island (Sardinia, Italy)

San Pietro island is located in the Western Mediterranean basin, 4 km off the southwestern coast of Sardinia. It was first populated in 1738 by a founder group coming from the island of Tabarka (Tunisia). Many researchers focused their attention on the population of San Pietro, because of its peculiar linguistic, genetic and demographic features. In this paper we analyzed data on surnames, matrimonial structure and genetic polymorphisms. All the data demonstrated a strong differentiation of San Pietro population when it is compared with other Sardinian or Italian populations. This differentiation is due to the isolation that for century characterized the island. Moreover, medical researches discovered a high incidence of a rare genetic pathology: the high myopia. This mutant gene was probably present in the founder group and then the isolation and the high rate of endogamy and consanguinity, highlighted by matrimonial structure analysis, could have determined its diffusion. Finally, our results suggested that San Pietro genetic diversity is strictly associated with linguistic and cultural diversity.     

Population structure of the Indian people: some microevolutionary aspects

Some aspects of population structure, namely village endogamy, marital distance and consanguinity in India are discussed. These parameters show social and geographic variation. The role of culture is of great importance in determining the mating pattern of a population. In the Indian situation, group endogamy in general does not cause inbreeding. Consanguinity is a cultural phenomenon of long-standing tradition, and so far there is no strong indication of a temporal change.     

Evolution of marital structure in 20 Sardinian villages from 1800 to 1974

This paper reports the data for endogamy, exogamy and consanguinity in 20 Sardinian villages from 1800 to 1974, divided into generational periods (25 years). The data are taken from the records of 48,262 marriages celebrated in the parishes of 20 Sardinian villages. The results for Spearman's rank correlation coefficient indicate significant positive correlations of endogamy with consanguinity (r(s) = 0.6551, percentage of consanguineous marriages; r(s) = 0.5477, Bernstein's alpha), with altitude (r(s) = 0.6386), with population size (r(s) = 0.2519), as well as a significant negative correlation of endogamy with time (r(s) = -0.4210). In addition, consanguinity shows a significant positive correlation with altitude (r(s) = 0.5717, percentage of consanguineous marriages; r(s) = 0.6295, Bernstein's alpha) and a significant negative correlation with time (r(s) = -0.2363, percentage of consanguineous marriages); the negative correlation between the mean level of consanguinity (alpha) and time is statistically not significant. In the single parishes, the levels of endogamy and consanguinity are generally higher in the mountain villages than in those situated in the hill and plain areas. Finally, it is hypothesized that, in the time period considered, the level of consanguinity and especially of endogamy were largely determined by isolation.     

Genetics,geography, and culture: The population of S. Pietro Island (Sardinia,Italy)

An interesting aspect of the island of Sardinia (Italy) is the wide range of genetic variability within the island itself. The variability is widened by the presence of some populations of different ethnic origin who speak a language other than Sardinian. This work deals with the study of the genetic structure of the Carloforte population which inhabits the tiny island of S. Pietro 4 km off the southwest coast of Sardinia. S. Pietro was first populated in 1738 by emigrants coming from the island of Tabarka (Tunisia) who spoke an archaic form of the Ligurian dialect. Data on genetic polymorphisms in the Carloforte population are presented and discussed in relation to some Sardinian and Italian populations. Data on demographic and matrimonial structure are also presented. The genetic analyses show the Carloforte population as being clearly separated from both Sardinians and continental Italians. The isolation of Carloforte, highlighted by language diversity, endogamy, and consanguinity levels and marriage area, supports the idea of genetic diversity linked to cultural peculiarity. © 1996 Wiley-Liss, Inc.     

Consanguinity and endogamy

This study distinguishes consanguinity, endogamy and social milieu. It reveals three facts: (a) the action of consanguinity is greater on mental capacities than on bodily dimensions; (b) endogmay, when distinguished from consanguinity, has on the contrary a more marked effect on body size than on mental abilities. This effect is additional to that of consanguinity; occasionally it exacerbates it (negative interaction); (c) the social milieu adds its effects to those of consanguinity and it explains the larger part of the endogamic depression.     

Causes of biological differences among social classes

The following research attempts to find biological differences among social classes is of interest, because it paves the way for practical applications and differs from the usual I.Q. polemics. In addition to well-known socio-cultural factors, this study provides a proof of the inhibitory effects of four other factors: matrimonial choices, consanguinity, natal prematurity and perturbations in growth rhythm, all of which are found more frequently in certain social classes.     

Impact of restricted marital practices on genetic variation in an endogamous Gujarati group

Recent studies have examined the influence on patterns of human genetic variation of a variety of cultural practices. In India, centuries‐old marriage customs have introduced extensive social structuring into the contemporary population, potentially with significant consequences for genetic variation. Social stratification in India is evident as social classes that are defined by endogamous groups known as castes. Within a caste, there exist endogamous groups known as gols (marriage circles), each of which comprises a small number of exogamous gotra (lineages). Thus, while consanguinity is strictly avoided and some randomness in mate selection occurs within the gol, gene flow is limited with groups outside the gol. Gujarati Patels practice this form of “exogamic endogamy.” We have analyzed genetic variation in one such group of Gujarati Patels, the Chha Gaam Patels (CGP), who comprise individuals from six villages. Population structure analysis of 1,200 autosomal loci offers support for the existence of distinctive multilocus genotypes in the CGP with respect to both non‐Gujaratis and other Gujaratis, and indicates that CGP individuals are genetically very similar. Analysis of Y‐chromosomal and mitochondrial haplotypes provides support for both patrilocal and patrilineal practices within the gol, and a low‐level of female gene flow into the gol. Our study illustrates how the practice of gol endogamy has introduced fine‐scale genetic structure into the population of India, and contributes more generally to an understanding of the way in which marriage practices affect patterns of genetic variation. Am J PhyAnthropol 2012. © Wiley Periodicals, Inc.     

Inbreeding and surnames: a projection into Easter Island's past

The population of Easter Island is one of the most interesting extant human communities due to its unique demographic history, its geographic isolation, and the development of an incomparable culture characterized by the towering "Moais" and its enigmatic writing. Following the colonization of its population by Polynesians from the Mangarevan Islands in the 5th century AD, the island remained isolated up until the middle of the 20th century. Under these conditions, with endogamy levels fluctuating between 61.04-96.54% and given such a small population, a high rate of inbreeding, and consequently, an elevated level of genetic relationships would be expected. Using data from church and civil records, we calculated the consanguinity of the population of Rapa Nui. The results of this analysis do not support the hypothesis of a high level of consanguinity (alpha = 0.00028 and F(t) = 0.0007, with F(r) = 0.00586 and F(n) = -0.00519), suggesting instead the existence of a strategy used to avoid marriage between close relatives. To explain these observations, the structure and exchange dynamics of the population were studied in the tribes, known locally as "Mata." The results of this analysis suggest a tendency toward the avoidance of inbreeding within tribes, in order to decrease the rate of endogamy in each group. This is consistent with ethnographic observations from the beginning of the 20th century that support the existence of strict regulations to prevent inbreeding between closely related individuals. Furthermore, we confirm that this situation dates back to a period before the "refounding" of Easter Island. Our results demonstrate that conditions of geographical isolation are not in themselves sufficient to produce an elevated inbreeding coefficient, revealing Easter Island as an interesting example of how cultural rules can shape the genetic structure of a population.     

Is the Central Valley of Costa Rica a genetic isolate?

In the last decade, the Costa Rican Central Valley population (CRCV), has received considerable scientific attention, attributed in part to a particularly interesting population structure. Two different and contradictory explanations have emerged: (1) An European-Amerindian-African admixed population, with some regional genetic heterocigosity and moderate degrees of consanguinity, similar to other Latin-American populations. (2) A genetic isolate, with a recent founder effect of European origin, genetically homogeneous, with a high intermarriage rate, and with a high degree of consanguinity. Extensive civil and religious documentation, since the settlement of the current population, allows wide genealogy and isonymy studies useful in the analysis of both hypotheses. This paper reviews temporal and spatial aspects of endogamy and consanguinity in the CRCV as a key to understand population history. The average inbreeding coefficients (a) between 1860 and 1969 show a general decrease within time. The consanguinity in the CRCV population is not homogeneous, and it is related to a variable geographic pattern. Results indicate that the endogamy frequencies are high but in general it was not correlated with a values. The general tendency shows a consanguinity decrease in time, and from rural to urban communities, repeating the tendencies observed in other countries with the same degree of development, and follows the general Western World tendency. Few human areas or communities in the world can be considered true genetic isolates. As shown, during last century, the CRCV population has had consanguinity values that definitively do not match those of true genetic isolates. A clear knowledge of the Costa Rican population genetic structure is needed to explain the origin of genetic diseases and its implications to the health system.     

Ace Alu insertion polymorphism in Croatia and its isolates

Alu elements are a family of interspersed repeats in the genome propagating by retroposition into new chromosomal locations. Alu insertion in Ace gene is known to be polymorphic (presence/absence of Alu element) in worldwide populations and as such serves as marker for population structure analyses. In this study we examined the distribution of genotypes and allele frequencies of this polymorphism in general Croatian population and its two isolates (the island of Hvar and the coastal region of the Middle Dalmatia) and related them to the level of endogamy as an indicator of inbreeding in these populations. Results showed that these three population groups are different with respect to Ace Alu polymorphism. The endogamy was highest on the island of Hvar. With the increase of endogamy a decrease in heterozigosity was observed. The same trend was observed for the frequency of insertion allele. Its frequencies in the village subpopulations of two studied isolates are subject to genetic drift due to small population sizes and high levels of endogamy. This in turn causes genetic differentiation among villages that is observed to be higher on the island of Hvar than in the coastal region. In the worldwide perspective, the Ace Alu insertion allele frequency of 50.6% in the general Croatian population falls within the range of other European populations.     

Class endogamy, inbreeding and migration during the Argentinean colonial period: analysis based on individuals of European ancestry

During the Spanish colonial period, Córdoba was an important town due to its location suitable for controlling communication throughout a wide region of Argentina. As a typical colonial society, where individuals belonged to a well established social class, marriages among Whites were the result of strict norms and prejudices founded on nets of kinship, friendship and neighbouring. The objective of this paper is to determine, whether the elevated class endogamy among Whites during the colonial period resulted in high consanguinity and whether a process of selection of surnames was present in 1813. In both cases the interaction with the migratory flow was taken into account. It is concluded that (a) Although an endogamy of "class" existed among Whites, there is no evidence of the consequences on the biological structure of the population through preferential mating between relatives, as deduced from the low level of inbreeding from isonymy. (b) There was no differential reproduction reflecting the selection of families carrying certain surnames; therefore surnames followed a "neutral" model. (c) The diversity of surnames and the gene flow deduced from them were of a magnitude similar to present populations; this fact could have balanced the effect of the "class" endogamy. (d) Finally, the congruence between information derived from the population age distribution and historic data and the quantification of migration from surnames allowed the detection of mistakes in the census data file regarding the number of foreigners, thus validating the use of surnames as biological markers of the population structure.     

Trends in inbreeding, isonymy, and repeated pairs of surnames in the Valserine Valley, French Jura, 1763-1972

The estimates of inbreeding derived from pedigrees and frequency of isonymous marriages (i.e., between persons of the same surname) are compared using genealogical and isonymic information from 4,899 marriages recorded between 1763 and 1972 in 4 rural villages of the French Jura region (a mountainous area near the Swiss border). Before the second half of the 20th century, the two kinds of estimates show a different temporal evolution. The mean inbreeding coefficient based on pedigrees increases between 1763 and 1852 and reaches a maximum between 1853 and 1882 (alpha = 0.0028), with a very low percentage (< 1%) the result of remote kinship. The mean inbreeding coefficient based on isonymy is always higher, with a maximum observed between 1793 and 1822 (F = 0.0200), and it remains roughly the same between 1763 and 1882 (F = 0.0150), with a high percentage resulting from a random component (Fr), a consequence of the small population size and genetic drift. After 1883, the 2 mean coefficients decrease. This discordance is largely explained by the poor quality, for the first periods, of the genealogical data base, which ignores the more remote links of kinship, justifying the use of the model of Crow and Mange (1965) to explore consanguinity during the more ancient periods. The temporal evolution of the repeated pairs of surnames index (RP) confirms the recent evolution of the marital structure of the valley. Moreover, it appears that isonymous marriages and repeated and unique pairs of surnames constitute 3 distinct matrimonial groups characterized by both a different mean coefficient of inbreeding (alpha) and a different rate of endogamy.     

Demographic structure and microevolution of an Italian alpine isolated population

The isonymic method has been generally accepted in population genetic studies and surnames have been successfully used to investigate human populations as if they were genetic markers associated to the Y chromosome. In this study we analysed the microevolution dynamics of Postua, a mountain village of North Western Italy, by means of demographic methods. The uniqueness of this community is due to its past geographical and cultural isolation and to the high frequency of marriage between relatives. During the study period considered (1640–1989) the population underwent several fluctuations in size and other demographic parameters such as the endogamy, isonimy and consanguinity rates. Until the first half of the XIX century Postua appears to be a village characterised by a closed and isolated community, with high endogamy (80–90%) and isonimy (up to 34.4%). Only at the beginning of the XX century, when the population started to be subjected to significant immigration fluxes, data show a progressive reduction of the isolation. The population showed two demographic peaks, the first around the second half of the XVIII century (1639 inhabitants) and the second at the end of the XIX century (1464 inhabitants). The S/N ratio was low (0.2–0.3) and relatively constant until the beginning of the last century, and only in the last three decades of the XX century, when the population was subjected to immigration, Postua showed a significant increase in the S/N ratio values (to about 0.9). The surname frequency was constant until the 1850 when almost all surnames were the same as those already present in the XVII century. From the first half of the XIX century, the founder surnames decreased, whereas new surnames started to increase and became persistent in the population.     

Inbreeding as measured by isonymy in two Venezuelan populations and its relationship to other variables

Isonymy is a useful approach to the study of population structure and thus can be utilized to detect deviations from random mating. In this study we give the results of an analysis of inbreeding levels and relate such variables as mean marital distance, surnames repeated in isonymous couples, and percentage of people using only maternal surnames to inbreeding and endogamy in two Venezuelan populations of black ancestry, Birongo and La Sabana. These populations differ in their sociocultural development and degree of isolation. We estimated inbreeding through isonymy and directly from genealogy. The most important findings are that the Ft values are higher than the a's, that the Fn component of Ft is higher than the Fr component, and that there is higher endogamy, inbreeding, and isolation in Birongo than in La Sabana. These results are in agreement with the sociocultural and historical background and development of each population. Nevertheless, both populations show similar temporal trends in almost all the variables analyzed. The use of isonymy as a complementary tool to study population structure is proposed, especially for Ibero-American populations.     

Marital mobility in populations of the High Aran Valley

The analysis of 2.623 marriage certificates in the towns in the High Aran Valley shows marriage mobility between the years 1650 and 1990 and indicates the level of population's endogamy. The results from the data collected in the town of Arties are presented as an example. The distribution of the places of origin of spouses and a factor analysis show a remarkable geographical endogamy until 1940. The results from marriage mobility are confirmed by data from blood polymorphism studies, matrimonial dispensations and surnames.     

Inbreeding in Finland

We have compiled data on the frequency of first-cousin marriages in Finland using royal dispensation records for the time period 1810-1872 and national population statistics for the time period 1878-1920. For the earlier period, 0.315% of Finland's marriages were contracted between first cousins (2,331 of 739,387). During the second time period, 0.174% of Finland's marriages took place between first cousins (1,325 of 761,976). These figures, which yield average kinship coefficients of 0.00020 and 0.00011, respectively, show that the level of inbreeding in Finland due to first-cousin marriage has been quite low. An analysis of individual parishes shows that first-cousin marriages are, on average, substantially less frequent than predicted by a random-mating model. In order to evaluate determinants of first-cousin marriage, several predictive variables have been examined: parish ethnic composition (proportion of Swedish and Finnish speakers), husband's occupation (graded into 6 socioeconomic levels), geographic distance between spouses' premarital residences, population density, parish endogamy, and urban vs. rural residence. Various logistic and linear regression models were analyzed in which consanguinity was the dependent variable. The best predictors of consanguinity were ethnic composition and occupation. The other variables were not in general significant predictors. These results show that many of the "mate availability" factors that would be predicted theoretically to account for consanguinity variation (population density, geographic isolation, urban vs. rural residence) do not. Instead, the best predictors of consanguinity at the first-cousin level are cultural factors such as ethnicity and occupation. Evaluation of cultural variables can provide a greatly enriched interpretation of complex biosocial phenomena such as inbreeding.     

Geographic, demographic and inbreeding patterns in a Basque mountainous region of Guipuzcoa

The Goierri, a mountain region within the Basque Hills of Guipúzcoa, includes one of the most culturally controlled autochthonous populations within the Basque area, mainly from linguistic point of view. The effects of geography and demographic changes (1862–1995) on consanguinity variables over its 21 Municipalities have been investigated. Rates of consanguineous marriages and mean inbreeding levels recorded in some of the southern villages can be considered high but, average values for the entire region were lowered due to the early industrialization of the province. In spite of that, consanguinity in the study area has been, for a long time, a prevailing and conspicuous phenomenon when compared to the other Guipúzcoa regions. The impact of marriages between first cousins from immigrant groups on the regional inbreeding levels represents an interesting result as well. Geographic and demographic factors seem to be related both to the extent of marriages as well as to the number of potential mates within populations, which, in turn, are associated with mean inbreeding levels. Altitude seems to show weak relationship with population distribution and population consanguinity variables. Nevertheless, levels of endogamy appear positively correlated with consanguinity rates and mean inbreeding coefficient and, inversely related-but not statistically significant- to mean village sizes. First cousin marriages yield the highest levels of exogamy and exogamous M22 marriages were mostly concentrated within short (1–10 km) and long-range marital distances (>50 km). The aveaage values of Goierri have been compared with a consanguinity data set of some selected Spanish mountain populations taken from the literature. One of the main results is that geographic and demographic variables are poorly correlated with the most important inbreeding parameters. However, different clusters of populations can be observed with specific characteristics for each of them, not highly correlated with geography.     

Fine-Scale Genetic Structure in the United Arab Emirates Reflects Endogamous and Consanguineous Culture,Population History,and Geography

The indigenous population of the United Arab Emirates (UAE) has a unique demographic and cultural history. Its tradition of endogamy and consanguinity is expected to produce genetic homogeneity and partitioning of gene pools while population movements and intercontinental trade are likely to have contributed to genetic diversity. Emiratis and neighboring populations of the Middle East have been underrepresented in the population genetics literature with few studies covering the broader genetic history of the Arabian Peninsula. Here, we genotyped 1,198 individuals from the seven Emirates using 1.7 million markers and by employing haplotype-based algorithms and admixture analyses, we reveal the fine-scale genetic structure of the Emirati population. Shared ancestry and gene flow with neighboring populations display their unique geographic position while increased intra- versus inter-Emirati kinship and sharing of uniparental haplogroups, reflect the endogamous and consanguineous cultural traditions of the Emirates and their tribes.     

A method for distinguishing consanguinity and population substructure using multilocus genotype data

We use the patterns of homozygosity at multiple loci to distinguish between excess homozygosity caused by consanguineous mating and that due to undetected population subdivision (the Wahlund effect). Clarification of the underlying causes of excess homozygosity is of practical importance in explaining the occurrence of recessive genetic disorders and in forensic match probability calculations. We calculated a likelihood surface for two parameters: C, the proportion of the population practicing consanguinity, and theta, the genetic correlation due population subdivision. To illustrate the method, we applied it to multilocus genotypic data of two U.K. Asian populations, one practicing a high frequency of cousin marriage, and another in which caste endogamy was suspected. The method was able to successfully distinguish the different patterns of relatedness. The method also returned accurate estimates of C and theta using simulated data sets. We show how our method can be extended to allow for degrees of inbreeding closer than cousin unions, including selfing. With closer inbreeding, the relatedness of recent ancestors beyond the parents becomes an issue.