From one generation to another generation, you would see people on the earth are strange or different. Some grew taller than 2 meters, some face looks just like an elephant (Indian), some have till six fingers, some have two legs, but one is the biggest and so on. Many people know that it is because of the genetic, some believe that it is because of the chemical effect on the gen, but the other different idea is that it is because of god up to the culture and their believe.
What are the reason that you think is reasonable and fact?
In this video, the doctor show a baby who born with the body joined at the waist. So there are two heads and bodies, but stuck together as one.