Your birthday is an inescapable mark, one of a small number of qualities in life you can never change, that accompanies you everywhere. Think about how often you write out or speak aloud those eight digits; they are one of the core confirmations of your identity, now and forever. I’m “Elijah Wolfson,” but to many I’m also “09/20/1985.”
The immutability of one’s nativity may be why so many are drawn to astrology—according to a 2009 Harris Poll, a full 26 percent of Americans believe in astrology (less than the number of UFO believers, but more than those that accept reincarnation as truth). Astrology builds on your birthday, giving it a meaning that goes well beyond that arbitrary 24-hour period so many years ago, of which you have no functional memory. It purports to help us understand the world through a system of relationships between astrological phenomena and human experience. Today, it takes its most popular form in the horoscope, found mostly in pop culture magazine and websites, and often focusing on foretelling the reader’s future in the realms of love and money.
But astrology was once a wholly scholarly and scientific endeavor. For example, medical astrology, or “iatromathematics,” stretches as far back as the field of medicine itself. “This is one of the longest standing intellectual traditions on the planet,” says Lauren Kassell, professor at the University of Cambridge’s Department of History and Philosophy of Science. Kassell researches the history of astrological medicine. “For centuries it was common practice for educated physicians to use astrology as one of their tools,” she says. Hippocrates, whose namesake oath is, to this day, still sworn to by all who enter the field, has been attributed to the saying “a physician without knowledge of astrology has no right to call himself a physician.”
These days, astrology has lost some of its luster, and is generally assumed to be bunk by the scientific community. Their argument: while its lush symbolism and universal symmetry were somewhat effective explanatory models back when we were in the dark, we now can see 13.2 billion light years into space and take picture of things half the width of a hydrogen atom, and it no longer seems particularly wise to choose when to operate based on where Jupiter sits in the sky.
But there’s something to astrology that rationalists have to contend with: The season of your birth, it turns out, appears to have a strong influence on your future. Depending on whether you were born in the spring, summer, fall, or winter, you could have a higher or lower risk for: schizophrenia, multiple sclerosis, sleep disorders, Type 1 diabetes, bipolar disorder, and allergies, among others. The season of your birth also seems to affect how long you live.
On their own, these individual studies could be the result of abnormal grouping, just random, scattered, clusters. But accumulated, a pattern emerges, begging the question: Is there any science behind the dusty old pickup line “what’s your sign?”
Many contemporary scientists are loath to admit to anything resembling astrology. “It seems absurd that the month you are born/conceived can affect your future life chances,” write neuroscientists Russell G. Foster and Till Roenneberg in a 2008 study. They then go on to then point out no fewer than 24 different health disorders connected to season of birth, and ultimately admit “despite human isolation from season changes in temperature, food, and photoperiod in the industrialized nations, the seasons still appear to have a small, but significant impact upon when individuals are born and many aspects of health.”
The problem may be that there’s no clear underlying mechanism for the observed phenomena. Theories range from levels of maternal vitamin D levels during pregnancy to seasonal viral and bacterial exposure.
“We know that there is this weird connection between seasonal birth and certain disorders, but we don’t know why,” says Chris Ciarleglio, a neuroscientist currently working as a postdoctoral fellow at Brown University. Figuring out the methodology, the “why,” is Ciarleglio’s primary research interest. A few years back, a team of researchers—John Axley, Benjamin Strauss, and Karen Gamble—working under Doug McMahon in the McMahon Lab at Vanderbilt uncovered perhaps the most compelling solution to date—one that, in theory, should please hard-line advocates of the scientific method and astrologers alike. It starts with a clock.
By now it’s popular knowledge that all humans have an internal clock or “circadian rhythm” that regulates our sleep/wake cycle. But this clock does much more than just tell us when to wake up every morning; it is central to all life functions. Cell growth, death, and reproduction; the functioning of digestive tissue, lungs, heart, and liver; patterns of social behavior—it’s all controlled by your biological clock.
If the clock is stable, things go according to plan: your body makes all its appointments. The problem is that no matter how perfectly genetically calibrated your clock, it’ll have to face the outside world, where a slew of environmental factors can permanently (and potentially negatively) alter how well it works. That’s where the season of your birth comes into play.