Sagging Fashion: Is Sagging Fashion a Yob culture or evolution?

From this to this

How did we get here? 

Sagging is thought to be a manner of wearing trousers or jeans that sag so that the top of the trousers or jeans are significantly below the waist thereby revealing much of the underwear. 

Sagging is predominantly a male fashion culture which originates in the 2000s.