A declaration up front: I don’t believe in astrology; not even a little bit.
But I like to apply my skepticism evenly. And there’s one thing that we astrology doubters like to stay that sticks in my craw.
“Only an idiot would believe that the month you are born could have any effect on your personality.”
Add me to the list of idiots.
It all started with schizophrenia. Some scientists noticed that schizophrenics were more likely than others to have February birthdays. Also, January and March birthdays. It wasn’t a huge effect, but it was statistically significant nonetheless. An schizophrenia definitely affects your personality.
Then scientists found the same for bipolar disorder – winter and early spring birthdays have it worst. They also noticed that incidence of these diseases was particularly low for people who were born in late summer and early fall. Suicidality (which closely tracks mental illness) appears to be strongest for April through June birthdays. Dyslexia may be strongest in the summer babies.
The first thing these scientists did is the same thing your or I would do. They looked at the Southern Hemisphere. They quickly found that these effects are reversed there. Since the seasons are reversed below the equator, it seems like weather has something to do with it. But what? So many things vary with the season. Disease levels, temperature, seasonal affective disorder, diet, activity level, many many organisms, pollen in the air, school attendance and consequent disease exposure, these things all vary with the season. Most research now focuses on temperature and on viral infections, especially the flu, but the mechanisms are still mysterious.
OK, but what about personality traits themselves?
A Japanese study found that people born December through February have lower agreeableness (this term has a precise definition to personality psychologists). A Swedish study found that (at least in women), February/March/April birthdays led to increased novelty-seeking behavior. Another study reported that summer-born males are less conscientious (another term with a formal meaning).
Now this doesn’t support astrology – not even close. From my limited knowledge, adjacent signs often have opposing, or at least unrelated, personalities, while science says that adjacent birth months are similar. And of course, no one thinks that the position of the stars in the sky has anything to do with it. It’s stuff happening her on earth that is the culprit.
But on the other hand, when someone says there’s no possible way the month you are born could have any influence on your personality, they aren’t exactly correct.
One final note. Schizotypal personality is also correlated with month of birth. And schizotypal personality (which is different from schizophrenia) may be associated with many personality traits. One of them is interest in, and belief in, astrology. So maybe there is something to the old joke: “I don’t believe in astrology, but then I wouldn’t. I’m a Gemini so I’m skeptical.”