"Maybe it's related to living inland. I'm not sure."
My mother's doctor explained to her that thyroid problems were common in people who came to Australia from landlocked countries in Europe. Lack of Iodine.
"Our mitochondrial DNA isn't actually our own DNA, but instead it's DNA of something our ancestors picked up ages ago."
I was not aware of that! If that is so, your theory makes a lot of sense IMO.
Virus (like AIDS) jumping the species barrier from monkey to human for example...
I used to think mtDNA came from the X of the XX/XY pair, as I knew it was inherited from our maternal side.
I try not to use Wiki for a resource too much, but when something isn't politically charged it can be useful...
http://en.wikipedia.org/wiki/Mitochondrial_DNA