Annals of Human Biology, May–June 2006; 33(3): 330–341
ORIGINAL ARTICLE
Reproductive pattern in consanguineous and non-consanguineous marriages in La Cabrera, Spain
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M. J. BLANCO VILLEGAS1 & V. FUSTER2 1
Departamento de Biologı´a Animal, Universidad de Salamanca, and 2Departamento de Zoologı´a y Antropologı´a Fı´sica, Universidad Complutense de Madrid, Spain (Received 21 July 2005; revised 20 December 2005; accepted 24 January 2006)
Abstract Background: Among determinants of the structure of human populations, consanguineous marriages can be useful in determining to what extent they influence the genetic structure of the population. This knowledge may be gained by comparing the reproductive performance of related and non-related couples. The population studied, La Cabrera, is a mountainous region in the Leon province (northwestern Spain). It includes four neighbouring municipalities with similar geographic, climatic and ecological features with 37 parishes occupying an area of 784.2 km2, of which only 1.5% is arable. The number of inhabitants remained stable from 1887 (9526 inhabitants) to 1960 (8984), when due to emigration it began to decrease. The average inbreeding coefficient ( ) for the period 1880–1989 (up to third degree) was 4.82 103. Aim: The objective of this analysis was to evaluate the possible factors determining the differences between consanguineous and non-consanguineous families residing in La Cabrera during the period 1880–1959. Subjects and methods: To study the structure and dynamics of each couple, families were reconstituted for the period 1880–1959 using demographic data corresponding to births, deaths and marriages obtained from parish registers. This procedure provided information on each couple’s reproductive history through information concerning the mates’ deaths as well as their offspring’s births and deaths. Principal component analysis revealed the existence of three factors that together explained 57% of the reproductive pattern variability of La Cabrera. Results: The first component (eigenvalue: 3.56) correlated positively with the number of live births and with the duration of the reproductive period. Component II (eigenvalue: 1.54) had a positive correlation with variables describing the beginning of the marital union, and with those indicating its ending. Finally, component III (eigenvalue: 1.13) reflected a negative association with the two variables that described neonatal and post-neonatal mortality. The above demographic variables represented the reproductive process in La Cabrera adequately. Fertility was the variable that offered the best explanation of the reproductive pattern (32%), followed by the marital structure (13%) and the infant mortality (12%). Conclusion: In the La Cabrera population, consanguinity appears as a socio-cultural process that affects the reproductive dynamic. Consanguinity modifies the marital structure and alters the reproductive
Correspondence: Ma Jose´ Blanco Villegas, Departamento de Biologı´a Animal (Antropologı´a Fı´sica), Facultad de Biologı´a, Universidad de Salamanca, Campus Universitario Miguel de Unamuno, 37071 Salamanca, Spain. E-mail:
[email protected] ISSN 0301–4460 print/ISSN 1464–5033 online ß 2006 Informa UK Ltd. DOI: 10.1080/03014460600627529
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pattern, prolonging the reproductive period, which results in a greater number of offspring. Lower infertility rates and the possible compensatory effect for infant mortality may reflect biological factors making the wife’s reproductive period more efficient. Keywords: Inbreeding, consanguineous marriage, fertility, marital structure, infant mortality, La Cabrera, Spain
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Introduction Among factors determining the structure of human populations, consanguineous marriages have recently received the most interest, taking two approaches: (1) by establishing the factors responsible for the incidence of matings among relatives depending on the society and its geographic, economic and demographic characteristics (Fuster and Colantonio 2002, 2003) and (2) by determining the extent to which they influence the genetic structure of the population. The above may be achieved by comparing the reproductive performance of related and non-related couples. In the case of significant differences, a knowledge of the causes involved is of value in order to verify the consequences on the genetic pool. Biological causality determining a positive association between family size and inbreeding (Schull and Neel 1965; Philippe 1973; Agarwala et al. 2001) has been widely discussed. Lower infertility rates among consanguineous matings may reflect higher fecundability (Rao and Inbaraj 1977; Bittles et al. 1991), and their more elevated fertility expression of a compensatory effect derived from greater infant mortality (Rao and Inbaraj 1977; Bittles et al. 1991; Hussain and Bittles 1999; Fuster 2003). However, the fertility levels found corresponding to consanguineous marriages are divergent among populations (Edmond and Braekeleer 1993). For this reason, the relationship between consanguinity and the reproductive pattern needs to be revised taking into account social and cultural aspects affecting the access to marriage, which may introduce variation on the marital structure and, therefore, on the population reproductive pattern. The population studied, La Cabrera, is a mountainous region in the south-eastern part of Leon province (north-western Spain). It includes four neighbouring municipalities with similar geographic, climatic and ecological features (Vila Valenti 1972) with 37 parishes occupying an area of 784.2 km2. The economy of La Cabrera (‘land of goats’) is poor, as only 1.5% of the total area is arable. In La Cabrera, steep mountain slopes and a limited road network kept this area in a condition of relative isolation. The population number of inhabitants remained stable from 1887 (9526 inhabitants) to 1960 (8984), when emigration to the most industrialized cities (Madrid, Bilbao, Barcelona, etc.) resulted in a rapid depopulation. In this period, endogamy was constantly higher than 85%, evidencing the marked reproductive isolation of La Cabrera (Blanco Villegas 2000). The average inbreeding coefficient ( ) for the period 1880–1919 was 6.78 103 (up to fourth degree) and for 1880–1989 (up to third degree) was 4.82 103. These values are very high in comparison with other Spanish and European populations (Blanco Villegas et al. 2004). In this paper the three factors defining a population reproductive pattern (age at marriage, fertility and infant mortality) are analyzed for consanguineous and non-consanguineous families residing in La Cabrera during the period 1880–1959. The objective of this analysis is to evaluate the possible factors determining the differences between their respective reproductive patterns.
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Materials and methods Demographic data corresponding to births, deaths and marriages were obtained from La Cabrera parish registers. The available total number of entries for the period 1880–1959 was 44 510, of which 23 427 corresponded to births, 16 112 to deaths and 4971 to weddings. To study the structure and dynamics of each couple, families were reconstituted following Fleury and Henry (1976). This procedure provides information on the reproductive history of each couple through information concerning the deaths of mates as well as the births and deaths of their offspring. Families were considered only when information about the death of both members of the couple was available, or only of one of them when the survival of the second was certain. For each family the information retained was: date, place and age at death in cases where it had occurred regarding parents; and sex, date and place of birth for their children, if any. Among 4971 weddings celebrated between 1880 and 1959, 2670 families could be reconstituted (53.71%). Of them 2196 correspond to unrelated couples and 474 to consanguineous marriages up to third degree. In both cases the bride’s age at wedding was 49 as a maximum. From each reconstituted family the following variables were calculated: age of husband and wife at marriage and at death, protogenesic and intergenesic periods (between wedding and the first delivery and between consecutive deliveries, respectively), live births, neonatal and post-neonatal infant mortality (first month and 1–12 months mortality, respectively), and effective and potential reproductive period (between the first and the last child born alive and between wedding and the wife’s 50th anniversary or until the death of one of the mates, respectively). In order to examine the interactions among the above variables, principal component analysis was applied using Pearson’s product-moment and Spearman’s rank correlations. Both methods provided similar results, but only the first is used in this study. To explore possible differences regarding fertility between consanguineous and nonconsanguineous families, a table of contingency (wife’s age at marriage vs live births) was generated after grouping the wife’s age at marriage into 5-year categories (10–14; 15–19 . . .). The elements of both matrices were converted to relative values by dividing them by the total number of marriages of each type (consanguineous and non-consanguineous). They were later subtracted to generate a matrix of differences. Finally, to determine the existence of any relationship between family size and infant mortality, a linear fitting between both variables was obtained for the percentage of children dying before 1 month of age as a function of different family sizes.
Results The principal component analysis reveals three factors that together explain 57% of variability in La Cabrera reproductive pattern (Table I). The first component (eigenvalue: 3.56) correlates positively with the number of live births and with the duration of the reproductive period, both effective and potential. These variables may therefore be considered as those determining the couple’s ‘fertility’. Component II (eigenvalue: 1.42) has a positive correlation with variables describing the beginning of the marital union: the ages of the husband and the wife at marriage and with
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Table I. Principal component analysis for variables defining the reproductive pattern of La Cabrera. Factors
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Variables BIRTHS ERP PRP AHM AWM AHD AWD NEOD POSTD INT PRO Eigenvalues Variance explained (%)
I 0.454 0.494 0.467 0.262 0.361 0.139 0.170 0.134 0.132 0.220 0.027 3.56 32.38
II 0.022 0.057 0.188 0.416 0.424 0.449 0.559 0.162 0.122 0.140 0.183 1.42 12.96
III 0.305 0.028 0.100 0.295 0.154 0.070 0.042 0.482 0.499 0.505 0.206 1.31 11.92
BIRTHS, children born alive; ERP, effective reproductive period, between the first and the last child born alive; PRP, potential reproductive period, between wedding and the wife’s 50th birthday or until the end of the marital union as a consequence of death; AHM, age of husband at marriage; AWM, age of wife at marriage; AHD, age of husband at death; AWD, age of wife at death; NEOD, neonatal or number of deaths during first month of life; POSTD, post-neonatal or 1–12 month mortality; INT, intergenesic period; PRO, protogenesic period between wedding and the first delivery.
those indicating its ending: mates’ ages of death. Quantitatively this component defines the ‘marital structure’. Finally, component III (eigenvalue: 1.31) shows a negative association with the two variables that describe neonatal mortality during the first month of life as well as during the remaining months until the first anniversary; this component represents ‘infant mortality’. The above demographic variables adequately describe the reproductive process in La Cabrera (57%). Fertility explains most variation (32%) followed by the marital structure (13%) and the infant mortality (12%).
Marital structure The marital structure is defined by means of variables determining the beginning and end of the marital union (Table II). The wife’s age at marriage was 25.63 and 26.70 for consanguineous and non-consanguineous marriages, respectively. For husbands the corresponding values were 28.81 and 30.39. In both cases these differences were not significant. Thus, an earlier access to marriage has been reported for consanguineous marriages. However, there are no differences for the ages at death for consanguinity. The husband’s mean age at death is 64 years and the wife’s 60, reflecting a larger proportion of widowers. The wife’s age at marriage distribution (Figure 1) is also different in related and nonrelated families. Consanguineous matings tend to occur at earlier ages (10–14 years, 0.63%; 15–19 years, 9.07%) than the non-consanguineous (0.22% and 7.87%, respectively). In addition, the percentage of cases corresponding to the age groups most represented (20–24 years) also differ: 42.41% and 37.89% for consanguineous and non-consanguineous marriages, respectively.
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Table II. Descriptive statistics for variables defining the reproductive pattern of reconstituted consanguineous and non-consanguineous families.
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Non-consanguineous
BIRTHS ERP PRP AHM AWM AHD AWD NEOD POSTD INT PRO
Consanguineous
n
Mean
SD
n
Mean
SD
t-value
p
2196 1868 2196 2149 2196 1674 1718 2196 2196 1886 1889
3.89 10.10 17.61 30.39 26.70 64.02 59.61 0.28 0.23 32.98 15.51
2.84 6.91 8.79 8.37 6.69 14.96 17.38 0.62 0.52 19.42 22.11
474 418 474 469 474 388 373 474 474 421 421
4.35 11.30 19.00 28.81 25.63 64.74 60.35 0.36 0.24 34.27 15.59
2.77 6.70 8.55 6.46 6.13 14.09 17.79 0.68 0.51 17.93 20.03
3.185 3.234 3.153 3.822 3.211 0.861 0.739 2.513 0.478 1.244 0.066
0.0014* 0.0012* 0.0016* 0.0001* 0.0013* 0.3891 0.4595 0.0120* 0.6324 0.2133 0.9468
n: number of completed families. BIRTHS, children born alive; ERP, effective reproductive period, between the first and the last child born alive; PRP, potential reproductive period, between wedding and the wife’s 50th birthday or until the end of the marital union as a consequence of death; AHM, age of husband at marriage; AWM, age of wife at marriage; AHD, age of husband at death; AWD, age of wife at death; NEOD, neonatal or number of deaths during first month of life; POSTD, post-neonatal or 1–12 month mortality; INT, intergenesic period; PRO, protogenesic period between wedding and the first delivery. *p < 0.05.
50
% marriages
45
Non Consanguineous
40
Consanguineous
35 30 25 20 15 10 5 0 10–14
15–19
20–24
25–29
30–34
35–39
40–44
45–49
Wife age at marriage
Figure 1. Wife’s age at marriage in consanguineous and non-consanguineous marriages.
Fertility Among consanguineous marriages fertility is significantly more elevated than in non-related: 4.35 live births and 3.89, respectively (Table II). Figure 2 shows the matrix of differences calculated from the family size according to the wife’s age at marriage. It is noteworthy that,
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Consanguineous
2
1
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0
−1 Non Consanguineous
−2 0
1
2
3
4
Wife age at marriage 5
6
7 Family size
Figure 2. Mother’s age at marriage non-consanguineous marriages.
vs.
8
9
10
number
11
of
12
13
offspring
40–44 30–34 20–24
10–14 14
in
consanguineous
and
with the exception of ages 15–19 and 30–34, consanguineous families have a lower percentage of infertility. Differences increase at the end of the reproductive period (35–39, 40–44, 45–49 years). However, differences are not significant regarding infertility: altogether 11.18% consanguineous couples had no offspring in comparison to 14.12% among nonconsanguineous couples ( 2 ¼ 2.86, 1 d.f., p ¼ 0.09). Considering only fertile couples, and in the absence of consanguinity, family sizes of two and three children predominate (9.47% and 13.10%, respectively), being less frequent in the consanguineous group (7.38% and 8.44%, respectively). The situation reverses when larger family sizes are considered: families with three to eight children are fewer among non-related couples (56.57%) than among related couples (65.69%). As expected, due to an earlier age at marriage, the potential fertile period is significantly higher in consanguineous marriages (19.00 years) than in non-consanguineous (17.61 years). The corresponding effective reproductive period used also differs significantly: 11.30 and 10.10 years, respectively (Table II). Finally, variables describing the interbirth intervals do not differ statistically between consanguineous and non-consanguineous marriages. First maternity takes place 15 months following the wedding and the average interval between two consecutive births was 33–34 months.
Infant mortality The mean number of children dying during the first month of life is significantly more elevated among consanguineous families (0.36) than non-consanguineous families (0.28). But for the postnatal period differences vanish: 0.24 and 0.23, respectively (Table II).
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% neonatal mortality
12
Non Consan = 7.14 + 0.08x Consan = 6.78 + 0.25x
10 8 6 4 Non Consan Consan
2
0
2
4
6 8 Family size
10
12
14
Figure 3. Neonatal mortality (0–1 month) vs. family size in consanguineous and non-consanguineous marriages.
Figure 3 shows the linear fit obtained after correlating the family size with the percentage of deaths occurring during the first month of life. Both for consanguineous (r ¼ 0.27, p ¼ 0.93) and non-consanguineous (r ¼ 0.18, p ¼ 0.56) the independence between both variables was found. Moreover, the W of the Wilcoxon non-parametric test, showed that the percentages of neonatal deaths did not differ statistically (Z ¼ 1.41, p ¼ 0.15) between consanguineous and non-consanguineous marriages.
Discussion Although consanguinity does not necessarily affect the marital structure through the age at ´ lvarez Edo et al. 1985; Edmond and Braekeleer 1993), in marriage (Alonso and Vigil 1980; A La Cabrera relatives marry earlier than non-relatives (wives 25.63 vs. 26.70 years; husbands 28.81 vs. 30.39 years, respectively). Evidently, depending on the structure of consanguinity (prevalence of certain types of matings among relatives), the effect of age may differ. The tendency towards more precocious marriages in the case of consanguinity—9.07% at 15–19 years and 42.41% at 20–24 (Figure 1)—is concordant with a cultural preference for certain close consanguineous matings, such as first cousins, which are not only accepted by the community but to a certain degree promoted for economic reasons in order to preserve the family property (Blanco Villegas et al. 2004). Concerning the reproductive process, in La Cabrera consanguineous families have higher fertility than the non-consanguineous families. This differential fertility is manifested in two ways: lower infertility rates and higher number of offspring among the fertile couples. In the case of consanguinity, the percentage of infertility is lower (11.18% vs. 14.12%). Taking into account the wife’s age at marriage, the above differences persist (Figure 2). Since in La Cabrera a pretransitional reproductive pattern existed during the period under study,
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contraception should be excluded in both groups of families; no social variable is known that could explain the previously mentioned differences in fertility. Therefore, the existence of a biological causality derived from a greater mother–foetus compatibility reducing the primary sterility and prenatal mortality rates can not be discounted (Bittles 2001). However, although a lower primary sterility among consanguineous families has been described by other authors (Schull et al. 1962; Yanase et al. 1973; Rao and Inbaraj 1977; Bittles et al. 1991) its quantification is difficult. The results for La Cabrera are much higher than the 5% as maximum reported in these papers, but are close to the 15% found by Rodrı´guez Otero et al. (1991) in another Spanish region. In our opinion, two factors are responsible for the different values reported for these populations: (1) methodological factors: in most studies the complete reproductive history is unknown (Edmond and Braekeleer 1993); and (2) factors associated with the contribution of the several types of consanguineous matings to the population inbreeding level, for instance the probability of marriages between relatives of a specific degree could occur at earlier/later age than nonrelated mates. More detailed studies taking into account these two factors are necessary in order to clarify the relationship of infertility and consanguinity. Among fertile couples, related marriages have a significantly higher number of children (4.35) than non-consanguineous marriages (3.89), which reflects the tendency towards more elevated family sizes (Figure 2). While two children was the most common family size among non-consanguineous families (13.10%) irrespective of the wife’s age at marriage, in the case of consanguinity the most common family size was five children (13.50%). According to Philippe (1974), the comparison of marital fertility is justified only in the case of homogeneous groups; in the two groups analyzed here the categories of ages most represented are the ones giving more heterogeneity to that distribution. Thus, in 37.89% of non-consanguineous matings women marry at ages 20–24; in the case of consanguinity they constitute 42.41% of the total. In this age range, consanguineous couples are much more represented in family sizes of 6–10 children. Higher fertility among consanguineous partners has been reported (Schull and Neel 1965; Reddy and Rao 1978; Bai et al. 1981; Khlat and Khoury 1988; Saha et al. 1990) as well as a positive association with larger family sizes (Philippe 1974; Agarwala et al. 2001); however, in our opinion, the causality attributed to inbreeding remains difficult to explain. The tendency of consanguineous marriages to more precocious weddings has extended the length of the reproductive period making possible more deliveries. In La Cabrera the reproductive period (effective and potential) is longer in the cases of relatives (19.00 and 11.30) than in non-relatives (17.61 and 10.10) (Table II). Although the timing for deliveries measured by the protogenesic and intergenesic intervals are very close in consanguineous and non-consanguineous matings (protogenesic: 15.59/15.51; intergenesic: 34.27/32.98, respectively), the longer reproductive period would have produced an increased number of progeny. In a recent review, Bittles et al. (2002) attributed consanguineous–nonconsanguineous fertility differences to the duration of marital union variability, a factor that in several pretransitional Spanish communities was revealed as a determinant of family size irrespective of consanguinity (Fuster 1986; Luna and Fuster 1990; Blanco Villegas 2000; Alfonso Sa´nchez et al. 2003). However, to accept this variable as the only factor explaining fertility differentials may be a simplification. The availability of a longer period for reproduction does not discard the action of complementary biological causality factors resulting in increased fertility. In this sense a higher fertility in the case of consanguineous couples has been attributed to a compensatory fertility that balances higher infant mortality in consanguineous families (Rao and Inbaraj 1977; Hussain and Bittles 1999; Bittles et al. 2001; Fuster 2003).
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In La Cabrera the mean number of deaths during the first month of life was significantly more elevated among consanguineous families (0.36) than in non-consanguineous ones (0.28); a difference concordant with other results reported for neighbouring communities ´ lvarez Edo et al. 1985; Rodrı´guez Otero et al. 1991). In contrast, for the period 1–12 (A months, both groups had similar averages (0.24 and 0.23, respectively). Irrespective of consanguinity, no relationship between the percentage of deaths during the first month of life and family size was found for consanguineous or non-consanguineous couples: the percentage of neonatal mortality is similar in large and small families. Despite a value among relatives (8.40%) slightly higher than among non-relatives (6.38%; Figure 2), the absence of statistical significance indicates that the risk due to genetic anomalies or to problems associated with delivery similarly affect both types of couples. In one way, the results obtained are contradictory: when neonatal mortality is expressed by its average value, statistical differences are found between consanguineous and nonconsanguineous families. On the contrary, if the family size is taken into account, such a statistical difference disappears due to the heterogeneity existing in family size for both types of couples. Thus, in consanguineous families the average neonatal mortality is significantly higher due to the fact that, in absolute terms, larger families had higher number of deaths. After correcting for family size, differences decrease, but a slightly higher neonatal mortality persists. Therefore, a compensatory effect against infant mortality can not be completely discarded since consanguineous matings show both a slightly higher fertility as well as a higher neonatal mortality. In the La Cabrera population, consanguinity appears as a socio-cultural process that affects the reproductive dynamic. Consanguinity modifies the marital structure and alters the reproductive pattern prolonging the reproductive period, which results in a greater number of offspring. Lower infertility rates and the possible compensatory effect for infant mortality may reflect biological factors making the wife’s reproductive period more efficient.
Acknowledgements Thanks are expressed to Erik Lundin for revising the manuscript.
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Re´sume´. Arrie`re plan: Les mariages consanguins sont des de´terminants de la structure des populations humaines qui en influencent la composition ge´ne´tique, ce qu’on peut appre´cier en comparant les performances reproductives des couples apparente´s et non apparente´s. La population e´tudie´e est celle de La Cabrera, une re´gion montagneuse de la province du Le´on (nord-ouest de l’Espagne). Elle comprend quatre municipalite´s partageant un meˆme contexte climatique, ge´ographique et e´cologique, incluant 37 paroisses occupant une aire de 784,2 km, dont seulement 1,5% sont arables. Le nombre des habitants est reste´ stable depuis 1887 (n¼9256) jusqu’a` 1960 (n¼8984), a` la suite de quoi le nombre commenc¸a de de´croıˆ tre suite a` l’e´migration. Le coefficient de consanguinite´ moyen (jusqu’au 3e`me degre´) est de 4,82.103 pour la pe´riode 1880–1989. Objectif: Cette analyse a pour but d’e´valuer quels sont les facteurs possibles d’une diffe´rence entre familles consanguines et non consanguines re´sidantes de La Cabrera pendant la pe´riode 1880–1959. Sujets et me´thodes: Les familles ont e´te´ reconstitue´es pour la pe´riode 1889-1959 au moyen de donne´es de´mographiques correspondant aux naissances, mariages et de´ce`s releve´s dans les registres paroissiaux. Cette proce´dure a apporte´ de l’information sur l’histoire reproductive de chaque couple. Une analyse en
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composantes principales a re´ve´le´ l’existence de trois facteurs qui expliquent ensemble 57% de la variabilite´ du sche´ma reproductif de La Cabrera. Re´sultats: Le premier composant (eigenvalue 3,56) est positivement corre´le´ au nombre des naissances vivantes ainsi qu’avec la dure´e de la pe´riode reproductive. Le deuxie`me composant (eigenvalue 1,54) est positivement corre´le´ aux variables de´crivant le de´but et la fin de la vie maritale. Le troisie`me composant (eigenvalue 1,13) exprime une association ne´gative avec les variables qui de´crivent la mortalite´ ne´onatale et postnatale. Les variables de´mographiques ainsi prises en compte repre´sentent de manie`re ade´quate le proce`s reproductif de La Cabrera. La fe´condite´ est la variable qui exprime au mieux le sche´ma reproductif (32%), suivi par la structure matrimoniale (13%) puis par la mortalite´ infantile (12%). Conclusion: La consanguinite´ apparaıˆ t dans la population de La Cabrera, comme un processus socioculturel qui affecte la dynamique reproductive. Elle modifie la structure matrimoniale et alte`re le sche´ma reproductif en prolongeant la pe´riode reproductive, ce qui conduit a` un plus grand nombre d’enfants. Des taux infe´rieurs de ste´rilite´ et un effet e´ventuel de compensation de la mortalite´ infantile peuvent eˆtre les reflets de facteurs biologiques qui font la pe´riode reproductive des femmes plus efficace. Zusammenfassung. Hintergrund: Unter den Determinanten der Struktur menschlicher Populationen ko¨nnen Ehen zwischen blutsverwandten Partnern fu¨r die Beurteilung, in welchem Ausmaß sie die genetische Struktur der Bevo¨lkerung beeinflussen, nu¨tzlich sein. Diesbezu¨gliche Kenntnisse ko¨nnen durch den Vergleich des Reproduktionserfolges blutsverwandter und nicht-blutsverwandter Paare gewonnen werden. Die untersuchte Population, La Cabrera, bewohnt eine Gebirgsregion in der Provinz Leon (Nordwest-Spanien). Sie umfasst vier benachbarte Kreise mit a¨hnlichen geographischen, klimatischen und o¨kologischen Strukturen mit 37 Gemeinden auf einem Gebiet von 784,2 km2, von dem aber nur 1,5% landwirtschaftlich nutzbar ist. Die Bevo¨lkerungszahl blieb von 1887 (9526 Einwohner) bis 1960 (8984) stabil, danach verringerte sie sich aufgrund von Abwanderung. Der mittlere Inzuchtkoeffizient ( ) fu¨r den Zeitraum 1880–1989 (bis zum dritten Grad) war 4,82 10–3. Ziel: Das Ziel dieser Analyse war die Beurteilung mo¨glicher Faktoren, die die Unterschiede zwischen blutsverwandten und nicht-blutsverwandten Familien aus La Cabrera wa¨hrend der Zeit 1880–1959 bestimmten. Probanden und Methoden: Um die Struktur und die Dynamik eines jeden Ehepaares zu untersuchen, wurden aus den demographischen Daten der Standesa¨mter zu Geburten, Todesfa¨lle und Eheschließungen im Zeitraum 1880–1959 die Familien rekonstruiert. Aufgrund von Informationen betreffend den Tod von Ehepartnern, sowie Geburt und Tod der Nachkommenschaft erlaubt dies Verfahren Aussagen zur Fruchtbarkeit eines jeden Paares aus der damaligen Zeit. Eine Hauptkomponentenanalyse zeigte drei Komponenten, die insgesamt 57% der Variabilita¨t des Reproduktionsmusters von La Cabrera erkla¨rten. Ergebnisse: Die erste Hauptkomponente (Eigenwert: 3,56) korrelierte positiv mit der Anzahl von Lebendgeburten und mit der Dauer der Reproduktionszeit. Die Komponente II (Eigenwert: 1,54) hatte eine positive Korrelation mit Variablen, die den Zeitpunkt der Eheschließung beschrieben und mit solchen, die das Ende einer Ehe kennzeichneten. Schließlich spiegelte die Komponente III (Eigenwert: 1,13) eine negative Assoziation mit den beiden Variablen wider, die die neonatale und die postneonatale Sterblichkeit beschrieben. Die genannten demographischen Variablen repra¨sentierten den reproduktiven Prozess in La Cabrera angemessen. Fertilita¨t war die Variable, die das Reproduktionsmuster am besten erkla¨rte (32%), gefolgt von der ehelichen Struktur (13%) und der Kindersterblichkeit (12%). Zusammenfassung: In der Bevo¨lkerung von La Cabrera scheint Blutsverwandtschaft ein soziokultureller Prozess zu sein, der die Reproduktionsdynamik beeinflusst. Konsanguinita¨t modifiziert die eheliche Struktur und vera¨ndert das Reproduktionsmuster, es verla¨ngert die reproduktive Periode, was zu einem Anstieg der Nachkommenzahl fu¨hrt. Eine niedrigere Infertilita¨tsrate und der mo¨glicherweise kompensatorischer Effekt fu¨r Sa¨uglingssterblichkeit ko¨nnten biologische Faktoren widerspiegeln, die zu einer ho¨heren Effizienz der reproduktiven Periode bei Frauen fu¨hren. Resumen. Antecedentes: Entre los determinantes de la estructura de las poblaciones humanas, los matrimonios consanguı´ neos pueden ser u´tiles para determinar en que´ medida influyen en la estructura gene´tica de la poblacio´n. Este conocimiento puede obtenerse comparando el comportamiento reproductor de las parejas emparentadas y no emparentadas. La poblacio´n estudiada, La Cabrera, es una regio´n montan˜osa de la provincia de Leo´n (noroeste de Espan˜a). Incluye cuatro municipios vecinos
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de caracterı´ sticas geogra´ficas, clima´ticas y ecolo´gicas semejantes, con 37 parroquias que ocupan un a´rea de 784,2 km2, de los cuales so´lo el 1,5% es cultivable. El nu´mero de habitantes se ha mantenido estable desde 1887 (9.526 habitantes) hasta 1960 (8.984), cuando debido a la emigracio´n comenzo´ a descender. El coeficiente de consanguinidad medio ( ) para el periodo de 1880-1980 (hasta el tercer grado) fue de 4,82 10–3 Objetivo: El objetivo de este ana´lisis fue evaluar los posibles factores que determinan las diferencias entre las familias consanguı´ neas y no consanguı´ neas residentes en La Cabrera durante el periodo comprendido entre 1880 y 1959. Sujetos y me´todos: Para estudiar la estructura y la dina´mica de cada pareja, se reconstruyeron las familias para el periodo 1880-1959, utilizando los datos demogra´ficos correspondientes a los nacimientos, defunciones y matrimonios obtenidos de los registros parroquiales. Este procedimiento proporciono´ informacio´n sobre la historia reproductiva de cada pareja a trave´s de la informacio´n relativa a los fallecimientos de los co´nyuges, y sobre los nacimientos y muertes de sus descendientes. El ana´lisis de componentes principales revelo´ la existencia de tres factores que, en conjunto, explicaban el 57% de la variabilidad del patro´n reproductor de La Cabrera. Resultados: El primer componente (valor propio: 3,56) se correlacionaba positivamente con el nu´mero de nacidos vivos y con la duracio´n del periodo reproductor. El componente II (valor propio: 1,54) tenı´ a una correlacio´n positiva con las variables que describen el inicio de la unio´n marital y con las que indican su final. Finalmente, el componente III (valor propio: 1,13) reflejaba una asociacio´n negativa con las dos variables que describı´ an la mortalidad neonatal y post-neonatal. Las variables demogra´ficas mencionadas representaban adecuadamente el proceso reproductivo en La Cabrera. La fertilidad fue la variable que ofrecio´ la mejor explicacio´n del patro´n reproductor (32%), seguida por la estructura marital (13%) y la mortalidad infantil (12%). Conclusio´n: En la poblacio´n de La Cabrera la consanguinidad aparece como un proceso sociocultural que afecta a la dina´mica reproductora. La consanguinidad modifica la estructura marital y altera el patro´n reproductivo prolongando el periodo reproductor, lo que resulta en un mayor nu´mero de descendientes. Unas menores tasas de infertilidad y el posible efecto compensatorio para la mortalidad infantil, pueden reflejar los factores biolo´gicos que hacen ma´s eficiente el periodo reproductor de la esposa.
