J. CYTOL. GENET. VOL. 18 (NS): 45–49 (2017)
EFFECT OF INBREEDING ON THE FERTILITY PROFILE OF SIX TRIBAL GROUPS OF IDUKKI DISTRICT, KERALA N. SINDU1 AND P. M. MATHEW2 1
Department of Botany St. Peter's College, Kolenchery 682 311, India 2 Perakathuseril, Muttada P.O., Thiruvananthapuram 695 025, India *For correspondance. Email:
[email protected] (Received 19 May 2017, accepted 26 May 2017)
SUMMARY Consanguinity study was carried out in six tribal groups of Idukki District, Kerala in relation to the impact of inbreeding on the fertility profile. Fertility data were assembled by degree of spousal relationship in terms of conception, livebirth and child survival. The overall mean fertility in consanguineous families registered significant differentials. The effect of inbreeding in the communities was discussed. Reproductive compensation, and longer cohabitation period alongside with other demographic determinants were suggested to be the causative factors for the increased rates of mean fertility in the tribal groups. Positive association between consanguinity rates and fertility profile was also evident. Keywords: Consanguinity, fertility, tribals, Idukki district.
INTRODUCTION Human inbreeding or consanguinity is referred to as the phenomenon of marital union between spouses who are related to each other by common ancestry. As the likelihood of two related spouses to possess the same genes inherited from the common ancestor is fairly high, inbreeding would result in higher frequencies of homozygous children in consanguineous families. The practice of inbreeding has implication on various realms of human life such as social effects, reproductive outcome in terms of fertility/fecundity and genetic effects in terms of prereproductive mortality and morbid conditions of genetic predisposition. Although an enormous quantum of data have accumulated on various effects of consanguinity in diverse population groups the world over, there has been little emphasis given to systematically studying the association between human fertility and inbreeding. This paper concerns the impact of inbreeding in fertility on six tribal communities of the Idukki district, Kerala. MATERIALS AND METHODS The tribal groups studied are Karavazhi pulaya, Kurumba pulaya, Mannan, Muthuvan, Urali and Ulladan. The tribals of the district are very poor and illiterate and socioeconomically undeveloped, living in isolated hilly forest tracts of the district, virtually cut off from the main stream communities. They are traditionally engaged in hunting, J. CYTOL. GENET. VOL. 18 (NS), NOS 1 & 2, 2017
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gathering and trapping birds and animals, and collecting forest products and honey. Some are engaged in agricultural labour, settled cultivation and animal husbandry. Almost all the tribal groups profess Hinduism and worship sprits and tribal deities. The data were collected by survey method from random samples ranging from 30–60% depending on the total family size, using a comprehensive questionnaire. The patterns of consanguinity incident among them are Uncle-Niece (U-N), Double First Cousin (DFC), First Cousin (IC), First Cousin once removed (I.5C) and Second Cousin (2C). The First Cousin pattern has four subdivisions such as patrilateral parallel cousin (PPC), matrilateral parallel cousin (MPC), patrilateral cross cousin (PCC) and matrilateral cross cousin (MCC), of which the cross cousin pattern is the most preferred. The frequency of consanguinity determined earlier (Sindu et al. 2001) in the tribals of the district are very high reaching very high levels (>80%) except in the Ulladan (12.74) tribal, of which the rate in the Kurumba pulaya (97.03%) is the highest ever reported. Fertility was measured in terms of three reproductive parameters such as conception, live-birth and child survival. Any married woman who had not produced a live-born after consummation was considered sterile and those who missed normal monthly period for five wks or more, considered pregnant.
OBSERVATIONS The frequency of inbreeding and the overall mean fertility in the consanguineous and nonconsanguineous families of the six tribal groups are furnished in Table 1. TABLE 1: Fertility data in six tribal groups of Idukki district, Kerala.
Tribe
Frequency consanguinity
Conception
Livebirth
Child survival
Mean fertility
Karavazhi Pulaya
89.68
NC C
2.44 2.96*
2.33 2.74
2.07 2.18*
2.44 2.96*
Kurumba Pulaya
97.03
NC C
2.00 2.71*
1.89 2.49*
1.67 2.06*
2.00 2.71*
Mannan
61.64
NC C
2.16 3.18*
2.14 3.10*
2.05 2.84*
2.16 3.18*
Muthuvan
91.45
NC C
1.65 3.62**
1.62 3.53**
1.53 3.09**
1.65 3.62**
Ulladan
12.74
NC C
3.08 3.17
3.02 3.11
2.82 2.81
3.08 3.17
Urali
55.65
NC C
2.71 3.86*
2.68 3.66*
2.59 3.27*
2.71 3.86*
NC-Nonconsanguineous, C-Consanguineous, *Moderately significant,
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**Highly significant.
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EFFECT OF INBREEDING ON FERTILITY
DISCUSSION Effect of human inbreeding on fertility has been a much debated subject, and there is still no convincing agreement on the matter. Available information has proposed three kinds of association between fertility and consanguinity. A few studies have reported lower fertility differentials among the inbreds (Afzel & Sinha 1984, Lazo et al. 1996) and many others significantly higher association (Bener & Alali 2006, Hussain & Bittles 2004, Kerkeni et al. 2007) and still others claiming no clear association (Rao & Inbaraj 1977). Many reasons have been suggested to explain the increased fertility rates on consanguineous marriages, which include operation of genetic, immunological, social and psychological factors. Sharing of common histocompatibility antigen (HLA) by related spouses is suggested to have a selective advantage during pregnancy owing to greater immunological compatibility of the mother and foetus. Two opposing hypotheses have been advanced in relation to pregnancy success such as (1) pregnancy initiated by consanguineous parents resulting in enhanced genetic compatibility between the mother and foetus due to greater proportion of shared maternal and paternal genes which in turn is beneficial to foetus survival and growth and (2) the foetal allograft concept, according to which a balanced polymorphism for transplantation of antigens is maintained via selection mechanism by which the antigenic disparity between the mother and foetus favour foetal development. Several genetic mechanisms also have been investigated to explain the mother-foetus compatibility hypothesis such as (a) the ABO blood group incompatibility, (b) the rhesus incompatibility and (c) the pre-clampsia involving components of the HLA system. A significantly higher rate of mother-foetus ABO incompatibility has been known in case of spontaneous abortion (Bandopadhyay et al. 2011). Some studies have reported prevalence of Rh incompatibility in consanguineous pregnancies favouring foetal/new-born survival (Stern & Charles 1945). Yet others have reported reduced levels of primary and secondary sterility in consanguineous couples suggesting intra-uterine mortality being lower in them leading to greater overall fertility (Philippe 1974). A range of proximate determinants exert direct influence on fertility including age of menarche ad menopause, sterility/fecundity, frequency of sexual union, induced abortion, lactational amenorrhea and postpartum abstinence (Wood 1989). Moreover a variety of socioeconomic and cultural factors also contribute in a modifying manner. As for the present tribal groups significant association exists between mean live-born profile and consanguinity for all degrees of spousal relationship. This was so in the case of many other tribal groups studied earlier from Kerala, and also in many other communities belonging to diverse social classes of the state (Joseph & Mathew 2002, Mathew et al. 2006). Reproductive compensation through replacement of an infant dying at an early age provide another convincing explanation for the positive association between fertility and consanguinity.This appears to have happened in several other Kerala tribal communities (Mathew et al. 2006, Jyothilekshmi & Sudhakaran 2012, 2014). The overall findings from diverse caste and communal groups of Kerala have displayed some sort of differring trend of association between couple fertility and consanguinity incidences, while some J. CYTOL. GENET. VOL. 18 (NS), NOS 1 & 2, 2017
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of the socio-economically developed communities have registered relatively low fertility mean and only marginal differentials; bulk of the less advanced and illiterate Scheduled Castes and tribals showed fairly significant differentials and higher mean fertility. A number of social and demographic factors can be implicated for the greater fertility profile of these communities which include younger maternal age at marriage, as in case of the present Idukki tribals, in which the increased fertility rate could be due to longer cohabitation period and consequent extended reproductive span. The enhanced reproductive fertility differentials known in the socioeconomically backward and marginalized communities like the Kerala tribals could be more a reflection of reproductive compensation and greater reproductive exposure span rather than representing any underlying biological difference in fecundity ascribable to consanguinity. There is a consistent positive association of the frequency of consanguinity with fertility in all the tribals except in Ulladan, in which the frequency is very low as compared with others. REFERENCES AFZAL M & SINHA S P 1984 Effects of consanguinity on fertility and mortality among Ansari Muslims of Bhagalpur Natl Acad Sci Litt 7 12 BANDOPADHYAY A R, CHATERJEE D, CHATERJEE M & GHOSH J R 2011 Maternal fetal interaction in the ABO system a comparative analysis of healthy mother and couples with spontaneous abortion in Bengalee population Am J Hum Biol 23 76–79 BENER A & ALALI KA 2006 Consangineous marriage in a newly developed country the Qatar population J Bio Soc Sci 38 239–246 HUSSAIN R & BITTLES AH 2004 Assessment of association between consanguinity and fertility in Asian populations J Health Popul Nutr 22 1–2 JOSEPH S & MATHEW P M 2002 Consanguinity studies in eight tribal populations in Kerala J Cytol Genet 3 (NS) 51–55 JYOTHILESHMI P & SUDHAKARAN M V 2012 Trends and prevalance of consanguineous marriages in Mudaliars of Palakkad district of the state of Kerala J Hum Ecol 38 1–5 JYOTHILESHMI P & SUDHAKARAN M V 2014 Does inbreeding lead to increased fertility mortality and morbidity among the tribes of Attapady of Palakkad district (Abstract) 26 th Kerala Science Congress 262 Wayanad Kerala KERKENI E, MONASTRI K, SAKET B, GUEDICINE M N & BEN CHEIKH H 2007 Interplay of socio-economic factors consanguinity fertility and offspring mortality in Monstair Tunisia Croat Med J 48 701–707 LAZO B C, CAMPUSANO & PINTO-CISTERNES 1996 Analysis of consanguinity in some population of Viregion Valparasio Chile from 1880–1969 Acta Cient Vernez 47 43–49 48
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