I am doing some research for a book idea I have... What are the actual biological facts about offspring produced by incest? I have heard it causes deformity. I have heard it makes the offspring more likely to have this disease/affliction/problem etc. I have also heard that it is all bunk, and there is no actual negative side (biologically speaking) at all. Do those risks of "side effects" (if there are any) increase/decrease with relations? For example, a child concieved with your sister/brother, or a child concieved with your father/mother, grandparents, great grandparents, cousins etc? If so, would it make a difference if it is your sister or your third cousin if the whole family were strictly incestual? No outside genes? Then there is evolution... What about incest over a long period of time? Let's say they strictly "keep it in the family" for hundreds of generations. What would be the benefits/drawbacks long term? If there are actually physical drawbacks, does anyone know why? As far I understand, the common belief in the scientific community is that all humans can be traced back to a single common source (or tribe) in Africa... How does that really differ from generations of incest? Thanks.