THE month of your birth could influence your prospects for having grandchildren, at least if times were hard. A study of impoverished Canadian women born in the late 1800s has shown that those born in June had most grandchildren while those with October birthdays had the fewest.
While the reasons for the effect are not entirely clear, it adds weight to evidence that environmental conditions early in life dramatically influence your health and survival prospects. For instance, studies have shown that babies who were undernourished in the womb, and those who grow slowly in their first year, have a high risk of heart attacks as adults (快猫短视频, 28 April 2001, p 6). And there鈥檚 evidence that your risk of developing diabetes, breast cancer or even an eating disorder varies depending on the month you were born. 快猫短视频s suspect seasonal variations in a pregnant mother鈥檚 diet, hormone levels or climate could cause this.
Biologist Virpi Lummaa of Cambridge University wondered if month of birth could influence your future contribution to the gene pool, altering how many children and grandchildren you have. To find out, she and Marc Tremblay of the University of Quebec in Chicoutimi looked at medical records for 3290 women born in the Saguenay region of Canada between 1850 and 1879.
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All the women had married in the region and had at least one child who鈥檇 also married in Saguenay. At the time, no one used contraceptives, and these women had an average of more than nine live births. Most of the women had fairly uniform lifestyles as peasant farmers.
Lummaa and Tremblay found that women born in winter, early summer or early autumn had most grandchildren, while those born in early spring, late summer and late autumn had fewest (see Graph). The differences were large, with women born in June having on average more than seven more grandchildren than those born in October.
Women born in June didn鈥檛 live any longer, on average, than those born in October. But the June babies went on to marry younger, reproduced over longer periods, had more live births and raised more children to adulthood (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2003.2507).
Lummaa speculates that mothers of winter babies had plentiful food in late pregnancy after the autumn harvests, giving birth to children who were healthier and more reproductively successful. But April newborns may have had poorer health because they were conceived during the August harvest, a time of hard physical labour. October babies may have suffered from being conceived in January, a time of austerity after Christmas feasts.
However, some other peaks and troughs in the data have no obvious explanation, Lummaa says. Whatever the reasons for them, she thinks her work builds on the evidence that environmental conditions during very early human development are crucial for later health 鈥� so much so that the knock-on effects can filter down through the generations.