Board Thread:Legitimate Canon Questions/@comment-27561374-20160107001848/@comment-4091815-20160107002512

The Dread Doctors  methods have not been explained in any detail.

As you stated, we know they choose "natural chimeras" for their experiments.

In the show's parlance, natural chimera means humans who have two different types of DNA in the same body. People who have organ transplants from anyone other than an identical twin would have two sets of different  DNA meaning they are "natural chimeras."

It's unclear why these are the favored subjects but they have been consistent throughout.