Estrogen in the Winter can be Tough.

UC Davis Psychologist Brian Trainor found that estrogen has completely opposite effects on aggression [in mice] depending on the length of daylight. Specifically, estrogen made mice less aggressive when daylight hours were kept long, simulating summer. But it made them more aggressive when daylight hours were short, simulating winter.
Hmm...so estrogen-rich office slaves who labor in windowless cubes are more likely to be aggressive during winter? Intriguing.