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INSTITUTE OF SOCIAL ANTHROPOLOGY — PUBLICATION NO. 1 1 



42.3 for all of Mexico in 1940 or the rates of 44.0 

 for Mexico and 46.3 for the State of Michoacan 

 averaged over the period 1936-40. The 1945 

 rate in Quiroga was an exceedingly high 55.06 

 per thousand of total population ; and the average 

 rate for 1940-45 was 47.1. Although more 

 females than males have been born in various 

 years, the superiority in number of males over 

 females is so marked in 2 or 3 years out of every 



5 that there are always more male than female 

 children born in any span of 3 years or longer. 

 For the period 1940 to 1945 the ratio of males 

 was 52.7 to 47.3 for females. What determines 

 the cyclic or eccentric predominance of one or the 

 other sex we do not know. 



There appears to be a certain rhythm or cycle 

 to births within the year. During the 6 years 

 1940 to 1945, there were 116 births in June, and 

 June was in the top 4 birth months in 3 of the 6 

 years; there were 115 births in January, and 

 January was one of the top 4 months in 5 of the 



6 years; there were 113 births in May, and May 

 was in the top 4 months in 3 of the years; and in 

 October there were 112 births, and October was 

 in the top 4 months in 3 of the years. There were 

 76 births in February, and February was one 

 of the 4 low birth months in 5 of the years; 

 March had 79 births, and was in the low group in 

 3 years; April had 80 births, and was low in 5 

 years; and there were 84 births in September, 

 which was in the low group in 2 years. From 

 high to low number of births the sequence is 

 June, January, May, October, July, August, 

 November, December, September, April, March, 

 and February. Although the addition of a few 

 more years of record might alter some of the 

 relative positions, it is clear that January, May, 

 June, and October are consistently the leading 

 birth months, and that February, March, and 

 April are the months of fewest births. From 

 these data we derive the conclusions that there 

 are the most conceptions in August, September, 

 and April, and the fewest in May, June, and July. 

 It is possible that these critical periods may have 

 some connection with the various seasons of 

 planting, cultivating, and harvesting of the 

 chief crops, but the relationships are not apparent 

 to us. It is possible that the May-June-July 

 period of transition from extreme heat and dryness 

 to the wet season with accompanying physiologic 

 reactions (including increase of pulmonary dis- 



eases and various fevers such as typhoid) may 

 have some bearing on the small number of con- 

 ceptions. Considered by sexes, the distribution 

 is somewhat different. There were the most 

 male births in January (60), May (59), and June 

 (59), and the fewest in March (41), November 

 (42), and December (42); while there were the 

 most female births in October (61), June (57), 

 and January (55), and the fewest in February 

 (28), April (29), and September (35). However, 

 a longer series should be studied before any con- 

 clusions can be made positively. 



MARRIAGES 



As has been mentioned, civil marriage is not 

 absolutely mandatory, therefore the records in the 

 civil registry are far from complete. For the years 

 that we examined, the number of civil marriages 

 in Quiroga and its ranchos were: 1945 — 60, 1944 — 

 59, 1943-— 12, 1942—34, 1941-^4, 1940—47, and 

 1939 — 62. We would guess that at least three- 

 fourths of the unions are now ratified with a civil 

 marriage, and nearly all of these civU marriages 

 are succeeded by a religious marriage. We made 

 no analysis of the civil marriage records excepting 

 as regards ages, and for this we considered only the 

 marriages in 1945 and 1944. In six of the 119 

 marriages the woman was the older, in six cases 

 the ages were the same, and in six cases the age of 

 the woman was not given. The greatest discrep- 

 ancies in age were in marriages between a man of 

 55 and girl of 19 (36 years), a man of 56 and a 

 woman of 32 (24 years), and a man of 39 and a girl 

 of 18 (21 years). The median difference in age is 

 4 years, the modal difference is 2 years, and the 

 average of the differences is 5 years. The males 

 ranged in age from 16 (which is the lowest per- 

 missible age for a male) to 56, with the median at 

 22, the mode at 21, and the average of the ages 

 24.8 years. The females ranged in age from 15 

 to 48. The most popular ages for marriage were 

 18 (the median and mode with 21 instances), 17 

 (17 cases), 15 (15 cases), and 16 and 19 {with. 11 

 cases each). Probably many of the girls listed 

 with an age of 15 actually were 14, which is the 

 lowest legal age for marriage of females. This can 

 be compared with ages of 12, 13, and 14 in a num- 

 ber of our States, such as Michigan, Mississippi, 

 New Hampshire, and New York. The favored 

 months for marriages (at least for civil marriages) 

 are April, November, January, and February, 



