Acause they are sick and tired of you perverts staring at their knockers. Did they ask for those things to suddenly appear on their chests and cause you guys to drool? ( Well yes they probably did. Every night they asked for a set that would make the high school quarterback sell his soul for a date to the prom.) But does that give you nerds an excuse to ogle? Well, yes it does, ogle away. Where as you, by holding your books down to the side, are saying, "Look how strong just one of my arms is. Now show me your hooters and I'll hold books in my other arm." I know where of I speak. In college the men's dorm were right next to the library, the women's dorms were way across campus. I could tell that cause my bunk was next to the window. In high school the library was a block away, with the bus stop to take me home right in front of it. As a nerd I checked out lots of books, ( and it wasn't just acause the librarian had a volumnuous set of rare folios. Tho I did hope she would be impressed by my selections.) I soon discovered that it was way easier to carry the books cradled in my arms, rather than slung to my side, which tended to make me walk in circles and miss the bus anyway. Besides by carrying the books in that manner, I exposed my arms, which were the only part of body not afflicted by acne.

I don't think they do, actually, but it's a sign of coy- and demureness. Which doesn't have to mean that they're coy or demure, just that they would like to be seen so.

This explanation comes from my wife. Men have more upper body strength than women. Its much easier for a woman to hold the books close to their body, above her waist, rather than to hold the books to the side. it apparently hurts their shoulders. From a mans point of view, i do not have a clue.

I think it is in relation to strength and comfort. As a man I feel confinement of my arms to cause them to ache where as a woman may find that her shoulder and arms don't have the strength to carry them around unsupported by their side.

Men have about 40% more upper body strength than women, and a much higher center of gravity, which means that they have the strength to absorb the shock when walking and correct for the weight imbalance. Women, with their lower center of gravity, and lacking the strength to absorb the shock, hold books close and centered, because this requires less strength and properly balances the weight.

Because the girl has a purse on her shoulder.