Peyronie's (sp?) syndrome is suffered by roughly 1% of the male populace; it is caused by calcium depositions within the penile tissue. I have no idea about the physiology, or why exactly this causes defomation. But the moral of the story, within a percentage of sufferers, the penis can assume severely bent/curved shapes which look anything but natural. And in the more severe cases, the deformations can make erections/intercourse painful. It is generally in these latter cases where men seek treatment, which can consist of getting injections in the penis to break up the depositions!