According to Wikipedia:
Seasonal affective disorder (SAD), also known as winter depression or winter blues, is a mood disorder in which people who have normal mental health throughout most of the year, experience depressive symptoms in the winter…
…prevalence in the adult population of the US ranges from 1.4 percent (Florida) to 9.7 percent (New Hampshire)
Apparently, it’s related to sunlight. (Thus the decreased percentage in Florida) This makes alot of sense. We spend a third of our lives asleep and sunlight plays a major role in that cycle. Plus, the energy from the sun is pretty influential on our lives. I have heard that living in very cloudy areas like Daly City, CA can cause additional levels of depression. Maybe this is why Vampires are always so grouchy.
What is amazing to me is that human beings, thousands of years ago figured this out and did something about it. They picked the darkest, coldest day of the year (Winter Solstice) and decided to make it a major holiday. They wanted to give presents and spread love to as many people as possible. This, I believe, was to specifically combat the effects described by Seasonal affective disorder. In other words, Christmas and New Years are solutions to the fact that its depressing in the deep winter.
Religion, in it’s original forms had very smart and positive motives. It’s really only later when the original meaning is lost that it becomes about your team versus their team. I admire the people who decided to give gifts on the Winter Solstice. It’s great UX design and brought fun to the most needed part of the year.