Seasons of Life by Russell Foster

Author:Russell Foster
Language: eng
Format: epub
Publisher: Profile Books Ltd
Published: 2010-03-24T16:00:00+00:00

8

TIMING REPRODUCTION IN HUMANS

In the Spring a fuller crimson comes upon the robin’s breast;

In the Spring the wanton lapwing gets himself another crest;

In the Spring a livelier iris changes on the burnish’d dove;

In the Spring a young man’s fancy lightly turns to thoughts of love.

ALFRED LORD TENNYSON, ‘LOCKSLEY HALL’ (1842)

In early Victorian England, when Tennyson was writing his thinly disguised poem about his love for a young woman, it was not just young men’s fancy that turned in spring: conceptions peaked in late spring/early summer. Unbeknown to him, men’s sperm quality is highest then, while in vitro fertilisation studies have suggested that the fertilisation and quality of the female embryos are highest during the spring and lowest in autumn (Vahidi et al., 2004).

Diligent studies of parish records and local and national censuses have built up a picture of the seasonality of conception and birth in several northern European countries, including Sweden, Finland, England, Germany and Holland, dating back well into pre-industrial, pre-contraceptive pill and pre-elective Caesarean times. Although there is some variation between countries, births tended to peak around the spring equinox, followed by a secondary peak in September and a low during November and December. This ‘European’ birth pattern is typical of agricultural populations at higher latitudes. It reflects a high frequency of conceptions in June and July and a low conception rate during the autumn harvest season (Lam & Miron, 1994). It is not by chance that June is still the most popular month in which to marry. The tradition began with the ancient Romans, when the month of June was named after Juno, goddess of women and marriage, who vowed to protect those who married in her month. A June or July conception and a subsequent early spring birth meant that the mother had recovered to some extent in time for the busy autumn harvest season in the following year.

Swedish records are particularly reliable, and in that country not only did this essentially pre-industrial pattern persist into the twentieth century rather than attenuating with increasing urbanisation and the corresponding rupture with the agricultural year, but in the years from 1969 to 1987 the peak-to-trough difference in monthly births was more than 30 per cent, nearly twice what it had been in the 1920s and 1930s. While Sweden clung tenaciously and unusually to the past, this is not so in Germany, where the birth peak has switched in the past 60 years from February and March to September (Lerchl et al., 1993).

The records in Louisiana in the southern USA also show a marked seasonality in birth. Unlike Sweden, the trough in the past has been in spring and the peak in autumn. This seasonal variation in Louisiana and in many of the states of the Union, even in higher latitudes, is difficult to explain in view of the seemingly reasonable explanations for the European pattern. In Louisiana the seasonal variance has been flattening in recent years, as the numbers of homes with air-conditioning has steadily increased. High temperatures

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