/usr/lib/X11 vs. /usr/X11R6/lib/X11

[shaul]

These 2 directories (/usr/lib/X11 and /usr/X11R6/lib/X11) seems to me an exact 
copy of each other. I could not find any link between them.
Can I rm --force --recursive --verbose /usr/lib/X11 ?
And if not, why ?
What are the possible explanations that I have 2 copies of the same directory ?
Are there any other files or directories that are duplicated somewhere else on 
my system ?