ok i got 2 "scientific" answers to my question, one comes from actually a person that studied psycology and the other from an engineer, but they are both the same, and i'll share them with you:

I actually worked with a prof on a yawning study. Yawning is contagious because it was used by humans and other animals to make sure that the whole group would go to sleep at the same time. So a herd of people would become sleepy from one person being sleepy and yawning and that way they all went to bed at once and got up around the same time too. Very practical and that's why yawning is so contagious.
N.

and

As far as I know, the contagious-yawning thing stems from the stone age.
When humans wandered around in groups, the yawning marked the beginning of bed time. It was important that the whole group fell asleep at the same time, to make the guards ready to protect the group. So basically, everybody yawned at the same time to go to bed together. That's why the contagious yawning developed in our genes.

Just another theory.
F.

so here we are

i'm seriously deciding to switch my topic of my PhD thesis.... :)