I believe that each birth order creates triggers for depression, whether you are first, last, or somewhere in between. For example:

I am the oldest of two children in my immediate family. I was always expected to be the go-getter, the best and the brightest and to be the most responsible (This includes thoughts of people outside the family). Therefore I felt that if I failed in either one of these areas, no matter how small this "failure" was, that I had let everyone in my family down.

My sister was the younger one. As such, she was expected to be irresponsible, to use her looks to her advantage (I can't count the times I heard people tell Barb, "come on, smile!" even if it was clear there was nothing to smile about), etc. She also heard time and time again how "brilliant" her older sister was. It's a lot to live up to (although she outclasses me in brilliance in a lot of ways). Therefore, her being responsible was overlooked and any irresponsibilty was magnified.

It took us moving out of the house when we went to college to realize that our brilliance and strengths lay in totally different arenas where we didn't have to compete. I am now a successful business executive (an area she's NEVER wanted to touch) and she's a brilliant scholar (I never wanted to be permanently in academia). It is up to the person to develop their own special niche or interests that they feel makes them stand out in some way, shape, or form. This could be sports, academics, volunteer work, etc. Just because you're the middle child doesn't mean you're doomed to be a boring failure that has to follow ANYBODY's footsteps.

some of it's magic
some of it's tragic
but i had a good life all the way......
~jimmy buffett