Reply to ‘Influences of maternal weight on the secondary sex ratio of human offspring’
Dipartimento Integrato Materno Infantile, Ginecologia e Ostetricia, Policlinico di Modena, Via del Pozzo 71, 41100 Modena, Italy
Email: cgancci{at}unimore.it
Sir,
Dr Jongbloet boldly maintains that our interpretation of present (Cagnacci et al., 2004
) and past (Cagnacci et al., 2003) data ‘threatens the obstruction and clarification of the many enigmas related to the primary sex ratio at conception and secondary sex ratio at birth’. We have reported that offspring of lighter women show a reversed sex ratio. Our interpretation is that a reduced energy store influences the reproductive axis to favour female offspring. This interpretation is supported by the direct relationship between sex ratio and caloric availability in diets throughout the world (Williams and Gloster, 1992) and by studies (Singh and Zambarano, 1997), also including rural African regions (Gibson and Mace, 2003), showing that the sex ratio is higher in women with a larger fat store.
The studies that Dr Jongbloet claims contradict our interpretation indeed seem to support it. The secular trend of sex ratio increase in Southern non-metropolitan areas in Italy (Astolfi and Zonta, 1999) and among the Black population in the USA (Marcus et al., 1998) probably indicates, and certainly does not contradict, that the sex ratio increases with amelioration of caloric availability and reduction of undernutrition. All other evidence cited by Dr Jongbloet to support his hypothesis also fit with the concept that male offspring are antagonized by the non-optimal conditions such as those induced by an earthquake (Fukuda et al., 1998), the East German socio-economic collapse (Catalano, 2003) or a bombing attack in Croatia (Zorn et al., 2002). In support of his hypothesis, Dr Jongbloet maintains that, although males are conceived in less than optimal conditions, reversal of the sex ratio may occur in most extreme conditions. Although the decline of the sex ratio was not linear and was evident only in the first quartile of body weight, this cannot be defined as an extreme condition, since it applies to 25% of women living in one of the wealthier areas of Italy. Similarly, the seasonal modulation of the sex ratio supports a fine modulation of the sex ratio exerted by environmental factors rather than an effect exerted only by extreme conditions. Dr Jongbloet maintains that our interpretation is incorrect because it seems not to fit with his theory based on the over-ripness ovopathy concept (Jongbloet, 2004). Although, the present data may or may not fit his interpretation, the seasonal modulation of the sex ratio does not seem to support his hypothesis, as already discussed (Cagnacci, 2003). Available evidence on sex ratio modulation, as well as our present (Cagnacci et al., 2004) and past data (Cagnacci et al., 2003) may be explained by theories formulated by other authors (Trivers and Willard, 1973; James, 2001, 2004).
References
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Cagnacci A (2003) The male disadvantage and the seasonal rhythm of sex ratio at the time of conception: Reply. Hum Reprod 18, 2492–2494.
Cagnacci A, Renzi A, Arangino S, Alessandrini C and Volpe A (2003) The male disadvantage and the seasonal rhythm of sex ratio at the time of conception. Hum Reprod 18, 37–46.
Cagnacci A, Renzi A, Arangino S, Alessandrini C and Volpe A (2004) Influences of maternal weight on the secondary sex ratio of human offspring. Hum Reprod 19, 442–444.
Catalano R (2003) Sex ratios in the two Germanies: a test of the economic stress hypothesis. Hum Reprod 18, 1972–1975.
Fukuda M, Fukuda K, Takashi S and Moller H (1998) Decline in sex ratio at birth after Kobe earthquake. Hum Reprod 13, 2321–2322.
Gibson MA and Mace R (2003) Strong mothers bear more sons in rural Ethiopia. Proc R Soc Biol 270, (Suppl 1), 5108–5109.
James WH (2001) The data sources which may help strengthen the epidemiological evidence for the hormonal hypothesis of sex determination in man. Hum Reprod 16, 1081–1085.
James WH (2004) ‘Over-ripeness ovopathy, sex ratio increase and sex ratio reversal a challenging hypothesis for sex ratio modulation': an alternative interpretation. Hum Reprod 19, 775–777.
Jongbloet PH (2004) Over-ripeness ovopathy: a challenging hypothesis for sex ratio modulation. Hum Reprod 19, 769–774.
Marcus M, Kiely J, Xu F, McGeehin M, Jackson R and Sinks T (1998) Changing sex ratio in the United States 1969-1995. Fertil Steril 70, 270–273.[CrossRef][ISI][Medline]
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Submitted on April 27, 2004; accepted on May 20, 2004.
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