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Horoscopes are perhaps the original guilty pleasure. For every culture throughout history that believed our fates hinge on our zodiac signs, there was a skeptic calling B.S. The Arab theologian Ibn al-Qayyim was questioning the validity of astrological methods way back in the 13th century.

Still, horoscopes can’t seem to die, tucked into the back pages of newspapers and dredged up by That One Aunt after the dessert cocktails at Thanksgiving. (“You’re a Gemini, you should should really put yourself out there this month.”)

If anything, they serve as more of a hedge than a doctrine—the rabbit’s foot of belief systems.

“Millionaires don't use astrology,” JP Morgan, the king of hedging, once said. “Billionaires do.”

Astrology is, of course, basically bunk. Which is why it’s surprising that a study presented at the European College of Neuropsychopharmacology over the weekend suggests that the month in which we were born can, in fact, have an important effect on our mood.

For the paper, Xenia Gonda, an associate professor at Semmelweis University in Budapest, asked 366 university students to fill out a questionnaire that aims to determine which of four kinds of temperaments they most personify. The questions included things like “My mood often changes for no reason” and “I love to tackle new projects, even if risky” and “I complain a lot.” She then correlated their answers with their birthdays.

She found that, “it seems that when you are born may increase or decrease your chance of developing certain mood disorders,” Gonda said in a statement.

Specifically:

·   Cyclothymic temperament (characterized by rapid, frequent swings between sad and cheerful moods), was significantly higher in those born in the summer, in comparison with those born in the winter.

·   Hyperthymic temperament—a tendency to be excessively positive—was significantly higher in those born in spring and summer.

·   Those born in the winter were significantly less prone to irritable temperament than those born at other times of the year.

·   Those born in autumn show a significantly lower tendency to depressive temperament than those born in winter.

We already know that seasons wield surprising influence over our attitudes and lives. There’s winter S.A.D., summer S.A.D., and a mental positivity boost we get from spending time outside in the spring.

But this suggests that something about the time of the year a person gestates can somehow affect their brain chemistry for the long-term.

It’s not entirely far-fetched. One previous study found that people who were in utero during warmer months were more likely to die from a specific type of wintertime heart disease. Mice born in winter were more prone to seasonal affective disorder than those born in summer.

A few years ago, British researchers found that schizophrenia and bipolar disorder peaked in people born in January, while people born in May were disproportionately prone to depression. This, of course, almost directly contradicts the current study's findings, which might be because self-report surveys are notoriously fallible.

We don’t know the exact mechanism for any of these phenomena, but researchers have suggested maternal infections, food availability during pregnancy, and sunlight exposure as possible reasons. Kids born in certain months might also be much younger or older than most of their classmates, and they may suffer bullying as a result.

Of course, none of this proves that your birth month (or anything else about your biology) is destiny. Unless you’ve been diagnosed with a mood disorder, this could just be an easy way to help explain away the foul moods and giddy spurts we all go through. Or it could be because Mercury is in retrograde.