Another example is that of sciatia, which is much more prevalent when your sciatic nerve takes one particular path to get through the glutes. Other routed methods and sciatia is much less likely to be debilitating.
So that's the reason behind the dick pics. I thought it was just to show off, but it's for identification. Makes total sense now.
A form of biometric authentication, perhaps? Assume one has a spare CT scanner or some such thing, and doesn't mind discriminating against roughly half of the population.
> Even identical males twins don't have the same penis structure/routing. Thanks for sharing your own personal example (I am the twin, in mine).