Jewish twins, specifically identical twins, were subject to many Nazi experiments regarding why such a event will occur. They were subject to harassment, as well as study control. Like most Jewish families, they were split away from the rest of their family, with those that were weaker sent to extermination camps, and those who were stronger to labor camps.
One of the most common experiments that was induced on identical twins was "nature vs. nurture" idea. One of twins would be brought up "normally", while the other was to be left to their own device. Differential data would be documented as to whether or not there was any change in the nature of the twins (as twins were known to be identical and very similar).
Of course, many of these experiments were inhumane, and the subjects were mistreated on a wide variety of natural rights.
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