J. biosoc. Sci. (2004) 36, 221–234 2004 Cambridge University Press DOI: 10.1017/S0021932003006230 CONSANGUINITY, CASTE AND DEAF-MUTISM IN PUNJAB, 1921 A. H. BITTLES*, S. G. SULLIVAN* L. A. ZHIVOTOVSKY*† *Centre for Human Genetics, Edith Cowan University, Perth WA 6027, Australia and †N.I. Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow, Russia Summary. The eﬀects of religion, population sub-division and geography on the prevalence of deaf-mutism were investigated using information collected in the 1921 Census of Punjab. The total sample size was 9·36 million, and comprised data on thirteen Hindu castes, seventeen Muslim biraderis and two Sikh castes. A two-way analysis of variance comparing males in Hindu castes in which consanguineous marriage was prohibited, with males in Muslim biraderis which favoured first cousin marriage, indicated major diﬀerences with respect to the patterns of deaf-mutism within each religion. In the Muslim population 9·1% of the relative variation in the prevalence of deaf-mutism was inter-biraderi, 36·8% between geographical regions, and 48·8% an interaction between biraderi and region, whereas among Hindus 46·8% of the observed variation was inter-caste, 12·8% inter-region and 33·6% due to caste–region interaction. From a wider disease perspective the results obtained with the Hindu community indicate the significant genetic diﬀerentiation associated with caste endogamy. As the overwhelming majority of Hindu marriages continue to be within-caste, it can be predicted that similar levels of inter-caste diﬀerences in disease frequency currently exist. By comparison, the lower level of inter-biraderi variation among Muslims is probably indicative of the dissolution of pre-existing caste boundaries and the resultant gene pool mixing that followed the large-scale conversion of Hindus to Islam during Muslim rule in North India from the 13th to the 19th centuries. Introduction Within Western societies there is a long tradition of antipathy to marriages between close biological kin, an attitude which originally seems to have been governed by religious rather than secular principles (Bittles, 2003). During the mid-19th century there was a major upsurge of interest in consanguinity in both North America and 221 222 A. H. Bittles, S. G. Sullivan and L. A. Zhivotovsky Western Europe. In the USA events were precipitated by a paper delivered to the 9th Meeting of the American Association for the Advancement of Science which called for urgent action to curtail first cousin marriage (Brooks, 1856). This view was strongly backed by Lewis Henry Morgan who in 1870 had published a seminal volume on marriage structure, with particular emphasis on consanguinity. Although Morgan and his wife were first cousins, the birth of an intellectually disabled son and the subsequent death of both of their daughters from scarlet fever seem to have persuaded him that consanguinity should be avoided (Ottenheimer, 1990, 1996). As President of the American Association for the Advancement of Science in 1880, Morgan’s opinions were influential in the subsequent prohibition of first cousin unions by a majority of US states. The controversy surrounding consanguinity also was widely debated in Great Britain with Charles Darwin, who had married his first cousin Emma Wedgwood, a leading protagonist (Bittles, 1994). Like Morgan, Darwin was a late convert to the belief that consanguinity should be avoided, since his comments on the subject were not published until six years after the birth of his tenth and last child (Darwin, 1862). The adverse biological eﬀects assumed to be associated with consanguineous marriage became important at an early stage in the controversy, with deaf-mutism a subject of particular interest. One of the first studies into the causes and prevalence of deaf-mutism was undertaken by Sir William Wilde, the father of the author and playwright Oscar Wilde. As Assistant Commissioner for the post-Famine 1851 Census of Ireland Wilde collected details on the numbers and circumstances of the deaf and dumb and reported a total of 4747 cases, with an estimated 170 parental couples who were related as first, second or third cousins (Wilde, 1854). Following Wilde’s pioneering work other studies into the prevalence of deafmutism were conducted in Great Britain and Continental Europe (Mitchell, 1862; Child, 1863; Darwin, 1875). However, most of these investigations were based on small population isolates and so the results were of restricted general application. They nevertheless attracted the attention of the British Government of India and from 1871 onwards a question on the prevalence of deaf-mutism was included in the Census of India. Data from these Censuses, which were conducted in each state on a decennial basis from 1871 to 1931, oﬀer the opportunity of examining possible associations between consanguinity and deaf-mutism in a large continental population. Furthermore, in the latter Census years the information was collected by religion and by specific community, whether caste for Hindus and Sikhs, or biraderi (literally translated as brotherhoods) for Muslims. Biraderis are organized on traditional social/occupational bases and for Muslims in Punjab they fulfilled a similar role to the caste system in Hinduism (Shami et al., 1994). The Hindus of north India strongly avoid consanguineous marriage (Kapadia, 1958) whereas consanguineous marriage is favoured by Muslims (Hussain & Bittles, 1998; Bittles & Hussain, 2000). Therefore a central aim of the study was to determine whether consanguineous marriage could be shown to be associated with a higher prevalence of deaf-mutism. In addition, the censal data were used to investigate if the patterns of deaf-mutism diﬀered between and within the co-resident Hindu and Muslim populations. Consanguinity and deaf-mutism 223 Subjects and methods The territory covered by the Censuses of 1871–1931 included the present-day countries of India, Pakistan, Bangladesh and Burma, with returns both from states and districts under direct British rule, and from the quasi-independent Native States governed by traditional rulers. The information from each state was collated, analysed and separately published by state and for India as a whole. From their inception the level of detail in the information collected was impressive, and every Census included data on deaf-mutism, blindness, insanity and leprosy, with additional questions as appropriate, e.g. on the prevalence of elephantiasis (filariasis) in Travancore in south-west India. The 1921 Census of Punjab was especially interesting since besides recording basic epidemiological data at state and district level, information also was separately collected by Hindu caste (n=11), Muslim biraderi (n=17) and Sikh caste (n=2) across each of the four major natural geographical sub-divisions of the province, i.e. the Indo-Gangetic Plain West, Himalayan, sub-Himalayan and North-West Dry Area (Fig. 1). The particular castes and biraderis were chosen because each was wholly or predominantly composed of Hindus, Muslims or Sikhs. Although as indicated by the Census Commissioners of the Census of India 1921, recent converts from Hinduism may have been inadvertently included within some Muslim biraderis (Middleton & Jacob, 1923). The total numbers of males and females sampled in each of the castes and biraderis across the four geographical zones of Punjab are listed in Table 1. Data on deaf-mutism from the 1921 Census of Punjab were abstracted from the Censal records held in the British Library, London, and analysed to simultaneously determine the relative roles played by religion, population sub-division (caste or biraderi) and geographical location (over the four zones illustrated in Fig. 1) in the prevalence of deaf-mutism. The statistical approach adopted was based on a two-way analysis of variance. To reduce the eﬀect of sampling errors, each observation with a population size of ,1000 was removed from the analysis. This step also was separately undertaken for observations with a population size ,10,000. The percentage frequency of deaf-mutes was computed for each caste/biraderi and for each of the four study regions, and a two-way analysis of variance performed on the frequency of deaf-mutism. The frequency of deaf-mutes in each caste/biraderi, c, in region, r, (pcr) was considered as a prime variable with the error [pcr (1pcr)] /Ncr, where Ncr is the size of the caste/biraderi in that region. The non-weighted average frequencies were then computed for each caste/biraderi over regions (pc), and for each region over castes/biraderis (pr). In the case of no additive interaction, the disease frequency in caste/biraderi, c, of region, r, would be expected to be the mean of both marginal frequencies. Therefore, the interaction deviation, dcr, has been defined as pcr (pc + pr)/2. The analysis then followed the usual procedure for analysis of variance (Scheﬀe, 1959). The analysis was run at two levels of censoring, with population sizes larger than 1000 and 10,000 respectively. Although a higher level of censoring reduces the sampling error in each cell of the data matrix, it also results in more empty cells. At least in the case of Hindus the caste component of variation is putatively genetic in origin, since hereditary caste divisions are believed to date back to the second millenium BC (Thapar, 1966) following the entry of Indo-European-speaking peoples Fig. 1. Map of the Punjab, 1921, indicating the four geographical sub-divisions: I. Indo-Gangetic Plain West; II. Himalayan; III. Sub-Himalayan; IV. North-West Dry Area, and individual states and districts. In the accompanying legend the states are numbered and named in bold, the districts in plain font. 224 A. H. Bittles, S. G. Sullivan and L. A. Zhivotovsky Consanguinity and deaf-mutism 225 into the north-west of the Indian sub-continent (McElreavey & Quintana-Murci, 2002). Analogously, the regional component can be interpreted as caused by variation in the ‘environmental’ conditions of the diﬀerent regions with, as indicated later, the eﬀects of soil erosion and the associated reduction in soil iodine levels a major factor in the Himalayan zone. The interaction component is the variation in frequency of the disease that is specific to both caste/biraderi and geographical region. Finally, the error component of the table represents the variation of the disease within each sub-community due to population size. Results As summarized in Table 2, a total of 9,362,881 persons were studied in the 46 constituent states of Punjab, 54·2% of whom were male and 45·8% female. Under-enumeration of females is a perennial problem in censuses and surveys conducted in South Asia and it is especially commonplace in north India and Pakistan where females are widely disadvantaged (Das Gupta, 1987; Bhutta, 2000; Clark, 2000; Winkvist & Akhtar, 2000). The degree to which women in Punjab were under-enumerated in the 1921 Census can be gauged from the high sex ratios calculated from Table 2 for each of the main religious communities: Hindus 1·183, Sikhs 1·147 and Muslims 1·181. By comparison, an overall tertiary sex ratio of 1·047 was reported for the 1921 Census of India (Dyson, 2001). Hindus comprised 38·2% of the total, Sikhs 0·9% and Muslims 60·9%, with a biased geographical distribution of the communities. Muslims formed large majorities in the North-West Dry Area and the sub-Himalayan zone, and there were similar numbers of Hindus and Muslims in the south-east Indo-Gangetic Plain West. By comparison, there was a large majority of Hindus in the north-east Himalayan zone (Census of India 1921, Punjab, 1923; see Middleton & Jacob, 1923), where long-term erosion associated with glaciation, snow and high rainfall has led to the leaching of iodine from the soil and a consequent low iodine content in locally produced food. However, the distribution of both religions across all four geographical regions eﬀectively controlled for this major environmental variable. The overall numbers and percentages of Hindus and Muslims who were deaf-mute are summarized by geographical zone in Table 3. As might have been expected given their preference for first cousin marriage (Hussain & Bittles, 1998; Bittles & Hussain, 2000), and the known recessive gene contribution to deaf-mutism, Muslims had a higher prevalence of deaf-mutism than Hindus in three of the four geographical regions investigated: the Indo-Gangetic Plain, the Himalayan region and among males in the North-West Dry Area (Census of India, 1921, Punjab, 1923; see Middleton & Jacob, 1923). But because of the much larger number of Hindus (n=924,789) than Muslims (n=84,872) in the Himalayan zone where deaf-mutism due to iodine deficiency was most common, in the Punjab as a whole the total prevalence of deaf-mutism was actually higher in the Hindu community (Table 3). The rates of deaf-mutism reported were much higher for males than females in all four geographical zones and across caste/biraderi boundaries (Tables 3 and 4). While no specific comment on this topic was included in the Census of Punjab 1921, the under-enumeration of females in disease returns had been extensively discussed in Totals Sikh Khalsa Ramgarhia Totals Hindu Ahir Arya Bania Brahmam Chuhra Dagi and Koli Ghirath Kanet Khatri Mahajan Rathi Caste/biraderi 29,788 3910 25,878 1,039,243 109,370 3483 182,512 291,589 326,921 5435 636 146 113,850 5301 — Male 25,608 2565 23,043 844,989 87,355 2424 153,299 227,083 275,464 4623 131 151 89,560 4899 — Female Indo-Gangetic Plain West 448 51 397 478,829 328 231 1700 116,371 2836 78,911 61,585 146,422 8521 2129 59,795 Male 129 36 93 445,960 92 233 1042 106,740 1753 74,737 57,728 137,381 6290 2014 58,220 Female Himalayan 16,218 1487 14,731 298,826 2061 20,595 18,236 113,150 38,675 776 8985 2187 83,094 11,059 8 Male 14,882 1244 13,638 253,758 1090 18,081 14,340 95,484 31,093 651 7995 1872 72,596 10,548 8 Female Sub-Himalayan 218 93 125 120,411 1388 3366 1877 27,868 40,671 13 33 — 45,143 37 15 Male 81 53 28 93,182 848 2471 1163 19,484 32,274 18 23 — 36,850 16 35 Female NW Dry Area 46,672 5541 41,131 1,937,309 113,147 27,675 204,325 548,978 409,103 85,135 71,239 148,755 250,608 18,526 59,818 40,700 3898 36,802 1,637,889 89,385 23,209 169,844 448,521 340,584 80,029 65,877 139,404 205,296 17,477 58,263 Female All Punjab Male Table 1. The study population by religion, caste/biraderi and geographical zone, Punjab 1921 226 A. H. Bittles, S. G. Sullivan and L. A. Zhivotovsky 313,290 14,375 10,750 121,992 33,990 68,751 61,637 51,704 79,359 12,908 16,775 40,027 29,585 10,502 39,959 89,374 109,979 1,104,957 Totals Male 911,573 257,655 11,013 9554 100,747 26,788 58,438 51,884 44,427 66,129 10,650 14,182 30,362 26,752 8,202 33,713 70,069 91,008 Female Indo-Gangetic Plain West Muslim Arain Awan Biloch Julaha Kashmiri Machhi Meo Mirasi Mochi Moghal Mussalli Pathan Qassab Qureshi Sayad Sheikh Teli Caste/biraderi 47,673 1168 19 6 26,134 1972 104 — 3565 233 632 18 3586 330 146 612 4855 4293 Male 37,199 959 7 1 23,282 1242 41 — 2488 205 355 16 1553 176 84 441 2757 3592 Female Himalayan 798,030 112,934 159,472 2333 101,260 51,066 16,499 204 24,589 69,212 29,045 38,202 43,329 7584 18,187 45,736 34,858 43,520 Male 707,789 91,048 147,614 2251 87,244 47,871 14,983 123 23,754 61,702 27,223 33,858 38,376 7152 17,260 43,330 26,851 37,099 Female Sub-Himalayan Table 1. Continued 1,186,606 169,774 57,040 276,848 101,316 3965 65,700 255 46,361 85,864 4580 138,833 60,417 27,162 23,135 46,351 15,827 13,178 Male 956,534 143,781 50,590 229,638 84,900 2787 54,756 242 40,133 71,958 3558 119,214 49,525 23,491 20,109 39,437 12,380 10,035 Female NW Dry Area 3,087,266 597,166 230,906 289,937 350,702 90,993 151,054 62,096 126,219 234,668 47,165 193,828 147,359 64,661 51,970 132,658 144,914 170,970 Male 2,613,045 493,443 209,224 241,444 296,173 78,688 128,218 52,249 110,802 199,994 41,786 167,270 119,816 57,571 45,655 116,921 112,057 141,734 Female All Punjab Consanguinity and deaf-mutism 227 Hindu Sikh Muslim All religions Religion 1,039,243 29,788 1,104,957 2,173,988 Male 844,989 25,608 911,573 1,782,170 Female Indo-Gangetic Plain West 478,829 448 47,673 526,950 Male 445,960 129 37,199 483,288 Female Himalayan 298,826 16,218 798,030 1,113,074 Male 253,758 14,882 707,739 976,379 Female Sub-Himalayan 120,411 218 1,136,606 1,257,235 Male 93,182 81 956,534 1,049,797 Female NW Dry Area Table 2. The study population by religion and geographical zone, Punjab 1921 1,937,309 46,672 3,087,266 5,071,247 Male 1,637,889 40,700 2,613,045 4,291,634 Female All Punjab 228 A. H. Bittles, S. G. Sullivan and L. A. Zhivotovsky Consanguinity and deaf-mutism 229 Table 3. The prevalence of deaf-mutism by religion and geographical zone, Punjab 1921* Indo-Gangetic Plain West Hindu Muslim Male Female 7·1 7·7 4·0 5·1 Himalayan Sub-Himalayan NW Dry Area Male Female Male Female Male Female 30·6 36·1 12·9 9·6 9·7 8·2 7·6 11·4 7·2 7·0 22·4 33·1 All Punjab Male Female 13·8 10·0 10·1 7·1 *Expressed as cases per 10,000. earlier Indian Censuses. For example, in the Census of Mysore 1871 it was stated that ‘Mohammedan households . had refused to give either the names or ages of their females’ (Lindsay, 1874); and the Census of Mysore 1901 noted ‘It is however surmised that the infirm women are not quite so rare but, that there was much reluctance and reticence in notifying the infirmity of females, especially in families where the Zenana or Gosha custom prevailed, whereby identification and personal verification were out of the question’ (Ananda Row, 1903). That is, the lower rates of deaf-mutism and other disorders recorded for females was a recognized and particular artefact arising from the seclusion of women. Major diﬀerences also were observed in the prevalence of deaf-mutism in diﬀerent castes and biraderis (Table 4). Individual prevalence rates need to be interpreted with caution as in some of the numerically small sub-communities, e.g. the Muslim Mochi in the Himalayan zone and the Hindu Rathi in the sub-Himalayan zone, they are based on very small numbers of aﬀected individuals. Given the prevailing reluctance to report females who were deaf-mute, the analysis of variance conducted on the prevalence of deaf-mutism was based on males only with marked diﬀerences observed between the patterns of deaf-mutism in Hindus and Muslims. The total variance in the frequency of deaf-mutism was 2·31 for Hindus and 1·05 for Muslims, indicating a much greater overall level of diﬀerentiation in disease prevalence between Hindu castes than Muslim biraderis in Punjab. As shown in Table 5, the composition of the variance also diﬀered significantly by religion; the average variance in the prevalence of deaf-mutism was 46·8% for Hindu castes versus just 9·1% for Muslim biraderis. By comparison, the variance between geographical zones was 12·8% in Hindus but 36·8% for Muslims. This diﬀerence between the two religions became even more striking when populations of less than 10,000 were removed from the analysis, i.e. Hindus 28·6% and Muslims 61·7%, probably because of a decrease in population size errors. The interaction between castes/biraderis and geographical region was significant for Hindus and Muslims at both levels of censoring, indicating the presence of specific interactions within each sub-community to the ‘environmental’ conditions encountered in the diﬀerent geographical regions. In all cases the calculated errors were small, strongly suggesting that the observed variations in the prevalence of deaf-mutism in the diﬀerent castes and biraderis were not due to population size. 230 A. H. Bittles, S. G. Sullivan and L. A. Zhivotovsky Table 4. The prevalence of deaf-mutism by caste/biraderi and geographical zone, Punjab 1921* Indo-Gangetic Plain West Caste/biraderi Sub-Himalayan NW Dry Area Male Female Male Female Male Hindu Ahir 7·6 Arya 2·9 Bania 8·7 Brahman 6·8 Chuhra 6·3 Dagi & Koli 35·0 Ghirath 15·7 Kanet 0·0 Khatri 6·3 Mahajan 0·0 Rathi 0·0 Totals 7·1 Muslim Arain Awan Biloch Julaha Kashmiri Machhi Meo Mirasi Mochi Moghal Mussalli Pathan Qassab Qureshi Sayad Sheikh Teli Totals Himalayan 9·3 7·7 7·4 7·5 7·4 9·9 2·9 6·8 6·3 4·7 9·5 5·8 7·8 5·7 8·8 9·0 6·3 7·7 All Punjab Female Male Female Male Female 3·0 0·0 4·9 3·6 3·8 23·8 0·0 0·0 4·8 0·0 0·0 4·0 0·0 0·0 11·8 28·3 17·6 44·2 43·5 26·8 18·8 4·7 17·2 30·6 0·0 0·0 0·0 15·4 5·7 39·1 30·7 19·7 14·3 5·0 14·3 22·4 24·3 12·6 12·1 13·5 14·7 0·0 16·7 68·6 10·0 6·3 1250·0 12·9 9·2 14·9 11·2 11·6 10·3 0·0 11·3 37·4 5·9 1·0 0·0 9·7 0·0 0·0 32·0 6·8 4·7 0·0 0·0 0·0 10·4 0·0 0·0 7·6 47·2 12·1 0·0 5·1 4·7 0·0 0·0 0·0 8·4 0·0 1142·9 7·2 7·8 9·8 9·2 12·7 7·0 43·2 39·9 27·4 8·7 4·3 17·4 13·8 3·5 12·9 5·4 8·2 4·5 37·9 28·2 19·9 6·1 1·1 14·9 10·1 5·8 6·4 3·1 3·3 2·2 5·7 4·4 7·7 3·8 6·6 9·2 4·0 6·4 1·2 6·8 5·7 4·7 5·1 17·1 0·0 0·0 45·5 58·7 0·0 0·0 5·6 214·6 15·8 0·0 13·9 0·0 0·0 0·0 6·2 65·2 36·1 62·6 0·0 0·0 33·5 48·3 0·0 0·0 16·1 0·0 56·3 0·0 0·0 0·0 0·0 0·0 25·4 55·7 33·1 9·1 9·7 0·0 13·4 4·9 3·0 0·0 13·0 6·9 13·1 11·0 12·0 2·6 10·5 9·0 6·0 11·7 9·6 7·1 6·8 26·7 10·7 7·7 1·3 0·0 11·8 8·8 3·3 9·5 10·9 4·2 7·0 6·5 7·5 12·9 8·2 9·5 8·1 12·2 13·6 0·0 14·0 0·0 12·9 13·6 2·2 9·3 8·1 15·5 13·8 13·2 6·3 12·1 11·4 7·2 6·1 7·3 8·6 0·0 7·3 0·0 6·0 8·1 0·0 5·9 5·5 7·7 8·5 6·6 5·6 7·0 7·0 9·3 9·1 11·9 13·8 6·3 10·9 2·9 10·2 9·4 9·8 9·7 8·8 10·4 11·0 10·3 7·9 9·6 10·0 6·6 6·6 7·3 9·4 6·2 5·9 4·4 8·1 6·9 4·3 6·9 6·8 6·6 6·6 6·6 6·6 8·3 7·1 *Expressed as cases per 10,000. Discussion Problems can arise in the analysis of secondary datasets and historical data collections need to be approached with particular care. Data collection problems were openly acknowledged by many Census Commissioners, especially in respect to Consanguinity and deaf-mutism 231 Table 5. Percentage contributions of caste/biraderi and geographical zone to variation in the frequency of deaf-mutism Source of variation Community size .1000 .10,000 Religion Total variance Caste/ biraderi Hindu Muslim Hindu Muslim 2·31 1·05 1·45 0·38 46·8 9·1 39·4 2·0 Region Interaction of caste/biraderi and region Error 12·8 36·8 28·6 61·7 33·6 48·8 31·4 35·7 6·8 5·3 0·6 0·5 information gathered on disease. For example, the Report of the 1911 Census of India stated ‘It must be admitted at the outset that the statistics of infirmities are very unreliable. The enumerators were not highly educated, and in spite of the care which was taken to supervise them, there must certainly have been errors in diagnosis.’ Besides the general diﬃculties encountered in enumerating females, there also was a problem in diﬀerentiating between inherited prelingual deafness, as opposed to deaf-mutism associated with birth trauma, and speech and hearing disorders that were primarily environmental in origin and resulted from dietary iodine deficiency. Although the distribution of goitre and cretinism in India had been meticulously mapped by McCarrison (1915), the influence of iodine deficiency disorders on health in the Himalayan region was not proven until almost 50 years later (Ramalingaswami et al., 1961). Environmentally induced goitre, cretinism and deaf-mutism remain endemic in the Himalayan region (WHO/SEARO, 1985), despite the introduction of salt iodination in India from 1962 onwards (Pandav & Anand, 1995). Nationally an estimated 167 million people are currently at risk of developing iodine disorders, 54 million have goitre and there are 2·2 million cretins caused by iodine deficiency (ICCIDD, 2001). The failure of the 1921 Census to demonstrate a specific relationship between consanguineous marriage and deaf-mutism can be ascribed to the variability brought about by environmentally determined iodine deficiency, which as described earlier displays distinct local and regional patterns of distribution. By statistically controlling for this non-genetic variability the present analysis has revealed strikingly diﬀerent patterns of deaf-mutism in the two major religious communities that are in keeping with their population structure, marriage practices and known histories. Within the Hindu population, the greater total variance and high between-caste variation in the prevalence of deaf-mutism reflects the rigid caste diﬀerentiation that characterizes Hindu society (Bittles, 2002a). The patterns of caste endogamy common throughout India has restricted gene flow between diﬀerent sub-communities and through time has resulted in the accumulation of specific mutations within individual castes (Bittles 2002b, c). 232 A. H. Bittles, S. G. Sullivan and L. A. Zhivotovsky By comparison, although a majority of Muslim marriages are intra-biraderi and consanguineous, unions between members of diﬀerent biraderis do occur, as was demonstrated in a subsidiary study of the 1921 Census of Punjab (Middleton & Jacob, 1922). Large-scale conversions from Hinduism to Islam, especially from the 15th to 18th centuries (Bittles & Hussain, 2000), also resulted in the eﬀective disappearance of converts’ pre-existing Hindu caste aﬃliations, which may in part explain the low inter-biraderi variance in the prevalence of deaf-mutism. The homogenizing influence of conversion to Islam on the gene pool has been demonstrated in Y-chromosome studies of the prominent Rajpoot biraderi in the Pakistan province of Punjab, with persons who either were born into diﬀerent Rajpoot clans or even diﬀerent Hindu castes recruited into a single biraderi (Wang et al., 2000). (Note that for this reason Rajpoots were omitted from the present analysis.) Conversely, as indicated in Table 2 the Muslim population was widely dispersed within Punjab, and the strong language and cultural barriers between, for example, the Pushto- and Hindko-speaking peoples of the North-West Dry Area versus Punjabi speakers in the other geographical zones, would have contributed to their high between-region pattern of variation in deaf-mutism. Despite their methodological limitations, the Census data collected between 1871 and 1931 remain the only comprehensive national source of information on the prevalence of deaf-mutism in India, and as an early example of genetic epidemiology the study undertaken by the Punjab Census Commissioners in 1921 was impressive in its scope and scale. The conclusions drawn from the Punjab study also showed considerable insight with, for example, the prediction that more than one gene for deaf-mutism must exist (Census of India 1921, Punjab, 1923; see Middleton & Jacob, 1923). In fact, 24 diﬀerent single-gene mutations causing deaf-mutism have so far been described (OMIM, 2002). With access to molecular genetic analysis, it will be interesting to see whether the diﬀerences in the prevalence of deaf-mutism between Hindu castes revealed in the 1921 Census can be correlated with diﬀerent forms of inherited prelingual, sensorineural deafness in the present-day populations of the Indian sub-continent, and in the many Indian, Pakistani and Bangladeshi migrant communities abroad. Acknowledgments Initial studies into this subject were undertaken with financial support from the Wellcome Trust, and the assistance of Dr T. D. Sambrook. The advice provided by Mr D. Plumb of the Oriental and India Oﬃce section of the British Library is gratefully acknowledged. An earlier version of this paper was delivered at the meeting Historical Demography of Ethnicity held in the California Institute of Technology, Pasadena, on May 13th and 14th 2002. References Ananda Row, T. (ed.) (1903) Census of India 1901, Vol. 24, Mysore, Part-1 Report. 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