Second reply to ‘A further note on the sex ratios of births conceived during wartime’

Branko Zorn

Center za andrologijo, Ginekoloska klinika, Ljubljanae-mail: Branko.zorn{at}kclj.si

Sir,

I congratulate Drs James and Bisioli for the rich discussion about the possible causes of sex ratio changes related to wars: proximate versus ultimate. Both refuse to give in and are probably right

However, until novel advances are made in this field, these explanations will continue to be highly hypothetical and do not permit any progress in the debate.The letter from James (2004Go) is only a mere repetition of hypotheses that have been discussed in a previous letter. These hypotheses lack tangible proof. I would like to be shown that high coital rates really exist during a war (even of long duration) and, if so, to what extent. Moreover, previous investigators did not find any association between the timing of conception and the sex ratio. Rather than shedding new light on the role of wars in sex ratio changes, James imposes his own interpretations.

The intricate proximate and ultimate causes acting at different levels as proposed by Bisioli (2004Go) cannot be ruled out. The theory of Trivers and Willard, suggesting that more females are produced when there are conditions that are worse for the health of the mother, was confirmed in numerous recent reports, but, our problem is still present: what is the reason for the decline in the sex ratio we observed after a short-term war?

I prefer the effect of psychological stress as an explanation for such a change for two main reasons. Firstly, evidence exists for a relationship between population stress and sex ratio changes (Catalano, 2003Go). Secondly, hormonal and environmental factors are involved in psychological stress and may interfere with the sex ratio. Due to psychological stress, the sex ratio may be altered through changes in sexual activity, changes in hormones around the time of conception and early in the pregnancy, and reduced semen quality. Moreover, psychological stress is supposed to have a negative impact on the male conceptus, resulting in an increased rate of male abortions. Of interest are the reports on female metabolic changes at the origin of sex ratio changes. Reduced sex ratio is related to a low pre-pregnancy weight and a greater weight gain during pregnancy, suggesting that non-optimal maternal metabolism negatively affects male conceptus survival (Cagnacci et al., 2004Go). Weight homeostasis and metabolic changes may also be a consequence of psychological stress, a term which is as yet too ambiguous, and which needs a stricter approach and use.

Only prospective study designs with a high level of participation, methodological rigour and well-defined stress indicators or other supposed aetiological factors would permit us to progress. It is important to understand the biological mechanisms of following on from psychological stress which affect reproductive function. Apart from resolving the curious problem of sex ratio changes. This will help to prevent the associated pathologies.

References

Bisioli C (2004) Reply to a further note on the sex ratios of births conceived during wartime. Hum Reprod 19,1495–1496[Free Full Text]

Cagnacci A, Renzi A Arangino S Alessandrini C and Volpe A (2004) Influences of maternal weight on the secondary sex ratio of hman offspring. Hum Reprod 19,442–444.[Abstract/Free Full Text]

Catalano RA (2003) Sex ratios in the two Germanies: a test of the economic stress hypothesis. Hum Reprod 18,1972–1975.[Abstract/Free Full Text]

James WH (2004) A further note on the sex ratios of births conceived during wartime. Hum Reprod 19,1495[Free Full Text]





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