If there are lots of people at your workplace that you know, who say "hi" in the morning, people who you chat with at the coffee machine, you're less likely to feel depressed.
If you work at a small workplace or alone and you happened to wake up feeling down, you're less likely to be cheered up. At least according to my experience.
If you meet very few people during the day and therefor have few interactions with other people, it puts much more responsibility on the people you meet.
It is obviously a basic need to be part of a group. If we look back on when people were living in a much more primitive environment, I'm sure that there were at least two situations that made people depressed and that still do affect us in the same way.
To be separated from people in your group, was probably very serious and it probably meant you would die unless you managed to find them again. Another serious scenario was probably if you were abandoned by the group, if you were frozen out, you were probably equally predestinated to die, unless you found and were accepted by another community.
So I don't care what people say. I'm sure it is natural to be down, when not having enough interactions with others. I'm very happy I have a teenager who is full of life living with me.
