Study of the Day: Your Birthday Season Could Affect Your Personality

Blame the winter blues on your birthday.

This ain’t your mother’s astrology.

Researchers have found that the season in which you’re born could actually have an effect on your personality and behavior. (Just not in the daily horoscope kind of way.)

Biologists at Vanderbilt University experimented on baby mice, raising them in one of two simulated seasons. The mouse pups were either kept in summer conditions—about 16 hours of light and eight hours of dark—or the inverse winter conditions of increased darkness.

Once weaned, the mice were then shuffled into new cycles: half the winter mice were switched to summer conditions and half the summer mice were switched to winter conditions. After four weeks, all of the mice were placed into 24-hour darkness to gauge the effect of their babyhood season on their biological clocks.

The results? Summer-born mice maintained a stable behavior, adhering to their ingrained schedules. Winter-born mice, on the other hand, were more fickle in their behavior. Those who were briefly switched to summer hours happily adopted and maintained the summer pattern.

Once full darkness hit, however, the winter mice were thrown into biological-clock chaos, sometimes trying to keep their summer schedule, sometimes just sleeping the day away.

So what does this have to do with us? Well, behavior is heavily influenced by the body’s biological clock, no matter what species you are.

Here’s researcher Douglas McMahon:

We know that the biological clock regulates mood in humans. If an imprinting mechanism similar to the one that we found in mice operates in humans, then it could not only have an effect on a number of behavioral disorders but also have a more general effect on personality.

The mice raised in the winter cycle show an exaggerated response to a change in season that is strikingly similar to that of human patients suffering from seasonal affective disorder.

In short, those of us born in winter months (like me) could be less stable and less able to adapt to new climates and seasons. Previous research has asserted that people with winter birthdays are often at higher risk for certain mental disorders.

The researchers write that there are “many factors that could be at play, including exposure to flu or other seasonal diseases.” But learning about the effect of light exposure may prove important for understanding how these disorders arise.

About Lu Fong

Lu Fong was a staff writer and blog editor for the Good Men Project in its formative years. As the requisite woman on staff, her hobbies included cleaning, cooking, knitting, fainting, and childbearing. Follow her on Twitter @lufong.


  1. Richard Wiseman mentioned this effect in his book “Quirkology”, but he refered to research on humans. Not sure if it was his own research or someone elses. The study concluded that if you were born in the summer and had your first months in warm weather you are more likely to be extrovert and have a more positive view of life, if my memory serves me.

    Now i see that this is a rather old post… Oh well, guess I can always post it since I’ve already written it.

  2. The photo used above is owned by Hallmark … not sure how it “legally” keeps popping up all over the net.
    Baby’s mother won a contest and was given prize money that gives Hallmark all legal rights to the photo.

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