pipe

I've done a lot of research and it seems that theres no proof that marijuana causes any permanent brain damage at all...but I'm wondering is why the brain develops a tolerance to marijuana if its not harmful to the brain. Wouldn't it make more sense that the reason the brain adapts and makes it harder for you to get high is because its getting damaged everytime you get high? I just dont see another logical explanation...why the brain make something that doesn't negatively affect it harder to obtain? I'd like to know WHY the brain develops tolerance to marijuana...in all these 'reports' from 'experts' on the net i've read claiming that pot doesnt affect the brain, I have yet to see an explanation of tolerance. Any help would be much appreciated...