Like a virgo
- 25 December 1999
- From New Scientist Print Edition.
AS A DIEHARD astrology sceptic—a common trait in Sagittarians—I never thought my birth date revealed much about anything, apart from pinpointing that fateful month all those years ago when my parents were feeling frisky. But now I have to consider that it may be responsible for my hopelessness at cricket, my rejection from medical school and the fact that I'm not tall enough to reach the top shelf in the supermarket. I'm also likely to live to a ripe old age, and although I'll probably grow fat if I do, at least I'm unlikely to get depressed about it.
Astrology has had an avid following since the year dot. It has played an important role in world affairs, even guiding the decisions of world leaders from Emperor Tiberius to US President Ronald Reagan. But for millennia, sceptics have relentlessly derided astrology as a pseudoscience that preys on our gullibility. While fans of astrology turn to the stars, scientists have been turning to statistics. And most scientific work casts astrology in a pretty dim light.
But a growing body of research shows that there might indeed be some curious seasonal trends in our physical and mental characteristics. A steady trickle of papers published in learned journals have claimed that the prevalence of all sorts of skills and traits varies with date of birth.
For a start, there are some intriguing trends in sporting prowess. A study by psychologist Ad Dudink of the University of Amsterdam found that English professional soccer players in the 1991-92 season were almost twice as likely to have been born between September and November as during the summer months. And it's not just footballers who can celebrate their birthdays en masse; cricketers are also fruits of the season. Stephen Edwards from the University of Wales, Swansea found that fast bowlers were more likely to have been born in the early part of the year—although for some reason, he found no such trend among spin bowlers.
These strange correlations aren't confined to sporting spheres. Another study from Swansea, found that children born in Britain during the summer were 50 per cent more likely to need special help at school. Two more studies, one from Portugal and the other from Italy, found that more medical students have birthdays between April and June than could be explained by chance alone.
A deeper trawl through the literature nets evidence for seasonal correlations in average height, weight and longevity. In 1998, Gerhard Weber of the University of Vienna completed a study examining the average heights of over half a million 18-year-olds conscripted into the Austrian army over a 10-year period. He found a striking relationship between average height and month of birth, with men born between March and May being on average 6 millimetres taller then those born between September and November.
Curiously, people born in winter tend to get fatter in later life, according to a study soon to be published by David Phillips of the Medical Research Council Environmental Epidemiology Unit (EEU) in Southampton. Winter babies also tend to live longer, according to Gabrielle Doblhammer of the Max Planck Institute for Demographic Research in Rostock, Germany.
Perhaps the most unusual seasonal effect is found amongst scientists who support revolutionary theories. It seems that academics who were quick to support controversial theories such as relativity and evolution tended to be born between October and April. "I wasn't actually looking at birthdays, I was trying to understand why scientific revolutions like relativity come about, but I suppose I was unconsciously clocking up patterns in my head," says Michael Holmes, a psychologist from Queen Margaret's College in Edinburgh, who published his study in
Festive frolicks
Why there should be any patterns at all is anyone's guess. One factor that confuses the issue is that birth and death rates fluctuate with the seasons. There is a peak in births in September—usually blamed on people getting carried away at Christmas and New Year festivities—and random rises in birth rates after prolonged power cuts or strikes by electricity workers. Harsh weather increases the number of deaths, and frail people often cling to life like limpets as they approach their birthday, only to give up the ghost shortly after. All these effects can skew the pattern.
But these fluctuations can't account for all the correlations that scientists find. Of course, there are more mundane explanations for variations in sporting and academic ability, such as the timing of birth in relation to the academic year and the start of the sporting season. But it's also possible that there is a biological basis to these trends. "It could have something to do with external influences like sunlight and temperature," says Weber.
Ideas like this are moving the study of seasonal effects out of the realms of astrology into the arena of epidemiology. A growing body of literature that has languished largely unnoticed for at least 70 years shows that the season in which you are born could influence your chances of developing diabetes, arthritis, heart disease, schizophrenia, depression and allergies such as hay fever and asthma.
"When I first published my results in the 1970s, people said this can't possibly be true," says Fuller Torrey a research psychiatrist at the Uniform Services University of the Health Sciences in Bethesda, Maryland. He has undertaken a review of studies relating to schizophrenia and manic depression from 1929 to the present day, and found that more people with these disorders were born between December and April than would be expected by chance. He points out that there are more than 250 studies now backing this trend. "Whatever hypothesis you use to explain schizophrenia needs to account for this," he says.
"The fact that seasonal effects exist shows that environmental factors might exist," says Patricia McKinney, an epidemiologist at Leeds University, who has researched childhood diabetes. "One interpretation is that there are more infections occurring during pregnancy and early life that have some role in the development of childhood diseases." The role of viruses could explain a lot here too, as their activity and prevalence varies with the time of year—as anybody who's caught a dose of the flu in winter will testify.
David Barker of the EEU in Southampton has done some of the pioneering work looking at how what happens to a fetus in the womb can influence later life (see
Of course, as with all statistical correlations, there is always the possibility of the odd spurious result. Rory Collins of the Clinical Trial Service Unit at Oxford University demonstrated this beautifully in his study on the effects of daily doses of aspirin on people who had suffered a heart attack or a stroke. He found that aspirin significantly decreased the risk of a second attack. But a less highly publicised facet of the work was that when Collins analysed the data in monthly blocks, split according to star sign, it looked as though giving aspirins to Geminis or Librans actually increased the risk of a second attack. "I still think our study shows it's good to give heart attack patients aspirin regardless of their star sign," says Collins.
These spurious findings show just how easily strange correlations arise purely by chance. If you divide the data from a study into enough different subgroups, eventually one particular group will contain people who, possibly for entirely different reasons, might show trends which contradict those emerging from the study as a whole. "Ours was just statistical sleight of hand to show how we could manipulate the data and get spurious results," says Collins.
So, where does all this leave astrology? Is there more to it than the sceptics would have us believe, or should it just be slung in the mumbo-jumbo dustbin of scientific history? Well, I'm afraid I'll have to leave that one up to you. My horoscope says that this week is a bad time for me to make important decisions.
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