"It's not astrology — it's seasonal biology"

"It's important to emphasize that, even though this sounds a bit like astrology, it is not: it's seasonal biology!"
— Professor Douglas McMahon, Department of Biological Sciences, College of Arts and Science, Vanderbilt University

The season in which babies are born can have a dramatic and persistent effect on how their biological clocks function, and actually result in changes in brain physiology which impact lifelong behaviour. That is the conclusion of a new study published online on 5 December 2010 by the journal Nature Neuroscience. The experiment provides the first evidence for seasonal imprinting of biological clocks in mammals. The imprinting effect, which was found in baby mice, may help explain the fact that people born in winter months have a higher risk of a number of neurological disorders including seasonal affective disorder (winter depression), bipolar depression and schizophrenia.

When you are born makes a difference to who you are, study shows

From Vanderbilt University News
Babies' biological clocks dramatically affected by birth light cycle

From Science News [citation]
Season of Birth May Have Long-Term Effects on Personality, Study Suggests

From the journal Nature Neuroscience [citation]
Perinatal photoperiod imprints the circadian clock