Reply to W. H. James

Allen, Gordon

doi:10.1017/s0001566000008527

Cited by 1 publication

(2 citation statements)

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“…It seems that, contrary to Allen [2], one might judge that DZ twin-bearers are, in general, more fecund than other women. I have noted above that DZ twinning is dependent on four parameters: coital rate, probability of fertilization given that coitus has occurred at the optimum time, probability of spontaneous abortion, and probability of double ovulation.…”

Section: The Fecundity Of Dz Twin-bearersmentioning

confidence: 80%

“…Allen reconciles this with his hypothesis thus: "While I suppose that psychological sexual arousal is generally more intense in connection with extramarital coitus than in marital relations, the frequency of sexual arousal is probably correlated somewhat with the frequency of coitus. Since ovulation does not ordinarily coincide with coitus in humans, psychological state during coitus would not be so important as the average state around the time of ovulation" [2]. Allen supports his case by offering results derived from a model.…”

Section: Allen's Hypothesismentioning

confidence: 93%

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Coitus-Induced Ovulation and Its Implications for Estimates of Some Reproductive Parameters

James

1990

Acta genet. med. gemellol.: twin res.

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It is estimated here that, at the time of conception, the mean coital rate of young women who subsequently bear DZ twins is about 6% higher than that of the general population of young married women. This differential seems too small to account wholly for the greater promptness in conceiving DZ twins. Accordingly, it is suggested that coital rate is associated with DZ twinning in two ways. The major link seems to be indirect and mediated by erotic response which causes an increase in gonadotrophin levels and thus in double ovulation. In a minority of cases, frequent coitus may give rise to DZ twins via superfecundation, but it seems that, in human beings, the corpus luteum of one ovum will usually inhibit fertilization of any further ova after a short interval. The evidence presented here, though indirect, seems to suggest that, under particularly erotic conditions, double ovulation is sometimes induced. It seems reasonable to infer that coitus also occasionally provokes or accelerates single ovulations, thus impugning some rhythm methods of contraception. But there seems no very good evidence that rape induces ovulation. Some notes are added on the implications of induced ovulation for estimates of fecundability and of the length of the fertile period.

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Section: The Fecundity Of Dz Twin-bearersmentioning

confidence: 80%

Section: Allen's Hypothesismentioning

confidence: 93%