well some of the agencies used to do it to see what the effect would be like on the twins. http://bbs.clutchfans.net/showthread.php?t=139082
that is quite sad... more than likely they... you know... man talk about never looking at someone the same again.
In the past, yes, but I am not aware of similar instances in this day and age. What IS common, however, is marriage within the same family (say first cousins, etc), but there is a practical side to it, mainly to keep the wealth within the same circle. I think this deserves its own thread: would you consider marrying within your extended family?