Longer daylight makes men aggressive

Gabriel Schreiber and colleagues at the Beer-Sheva Mental Health Centre and Ben Gurion University in Israel have shown that psychiatric patients are more aggressive during longer days. Extended periods of light may affect brain chemistry, says Schreiber, increasing the release of neurotransmitters such as serotonin, associated with aggression.

Schreiber and his colleagues have studied more than 2,000 different wars and found a striking correlation between the opening dates and the length of day. Schreiber ackowledges that more wars may begin during the summer in part because armies prefer fighting in good weather. But he believes that light affects our biological clock, which regulates behaviours and bodily functions ranging from alertness to sex drive.