European Stars and Stripes (Newspaper) - October 23, 1990, Darmstadt, Hesse                                Seasonal signals of Fertility by Natalie Angier new York times songbirds mate in Spring and their nestlings Hatch in Masse a month later. Sheep conceive in fall carry their Young for six months and by Early Spring the Fields Are alive with the sound of bleating lambs. A great number of species Are seasonal breeders cued by the length of the Day a softening of the wind or other environmental factors signalling the arrival of the optimal time for Breeding. By contrast humans have Long been thought to be beyond the Sway of the seasons. After All people can and do reproduce any Day of the year. But in a comprehensive report in the journal of reproductive rhythms researchers present a wealth of data showing that human Fertility rates Are also influenced by the  say the two outstanding factors affecting reproduction rates Are the amount of sunlight and the temperature. Calculating Conception rates by studying birth records from around the world the scientists say that while human reproduction is far less seasonally dictated than that of other creatures it rises and Falls in distinct patterns throughout the year. Other researchers have noted peaks in birth figures that seemed too Large to be Mere statistical blips. But they dismissed such Fertility spikes As the artefacts of human culture perhaps spurred by holidays and ceremonies that give people the Leisure and official Blessing to mate. The new report insists annual variations in human Conception rates Are seasonally determined. The researchers show Peak Fertility times vary from one latitude and climate to another. They say geographical discrepancies reflect when people in those places Are exposed to a mix of Daylight and temperature that most closely approximate Ideal conditions for human Conception. According to the new analysis the perfect time of year to conceive is when the Sun shines for about 12 hours and the temperature hovers Between 50 and 70 degrees fahrenheit. For reasons that remain mysterious such conditions somehow help stimulate either ovulation in women a burst of sperm production in men or a combination of the two. In some regions of the world the scientists say people mating in the optimal Fertility season have twice the Chance of conceiving than they might have had the rest of the year. Quot what we think we be shown is that the rhythm of human Conception cuts across All cultural religious and social barriers Quot said or. Till Roenneburg of the University of Munich in Germany who wrote the report with or. Jurgen Aschoff of the Max Planck Institute. Quot the basis for this rhythm is a biological  other scientists while stressing humans Are truly Fertile year round say the results Are persuasive. Quot Many studies have shown that there is an annual periodicity in reproduction among animals Quot said or. Robert b. Barlow jr., a neuroscientist at Syracuse University and at the Marine biological Laboratory at Woods Hole mass. A what Hasni to been clearly shown is that a similar phenomenon occurs in humans. This study is the most exhaustive careful study to show that what applies to animals in general is also True for  but the researchers have also discovered that the influence of the seasons has flagged considerably with the Advent of industrialization As Ever More people spend most of their time under artificial Light and kept artificially heated or cooled. They say the changes May partly explain rising infertility rates in Western nations As Well As other hormonal problems linked to the endocrine system. Quot the effects of climate and Day length Are becoming less effective in the modern world because we re always indoors and the lighting and temperature Are controlled Quot said Roenneburg. Quot and you can see it happening statistically in our data. The Impact of the elements is going Down the  in the new study the scientists scrutinized birth records of 166 countries representing tens of millions of births. Studying the United states and Europe and the other countries of the temperate zone in the Northern hemisphere the researchers found there Are two annual Conception peaks which continue today but were especially notable before the Era of extensive industrialization. One statistical Spike occurs around the Spring Equinox in March resulting in a spate of births in late december or Early january. The second arrives in autumn around october or november leading to a slight glut of babies arriving in Midsummer. The Conception peaks blur slightly in one direction or the other depending on weather conditions of a particular Region. For example in the United states Spring is colder than it is in Europe and so the first Conception Peak Here occurs somewhat after the Vernal Equinox when the temperature is becoming a bit Palmier. But in Europe where the later fall is often Chilly and drizzly the second reproductive Peak is earlier than in the United states corresponding More closely to the autumnal Equinox in september. The Ideal Conception Day said Roenneburg is Quot the sort of Day in Spring or autumn when you have Nice nights and Days that Are agreeable and  the researchers have yet to determine Why human Fertility rates respond to seasonal signals. In experiments with other animals they have correlated Day length with hormone Levels in both males and females. Studying the siberian Hamster or. Fred w. Turek a professor of neurobiology and physiology at Northwestern University in Evanston iii., found that when the rodents were placed under lighting conditions mimicking a summery 15 hours of Sunshine the Levels of testosterone in the male would soar. The change prepared the male to mate at a time when any pups he sired would be born two weeks later when the weather would be gentle and the food abundant. Quot there s a tremendous selective pressure to maximize the survival of the Young Quot turek said. Quot for a Hamster to have offspring in midwinter might be a Complete waste of Effort. 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