SOmething along the lines of that but perhaps through genetic engineering it could happen I know that a mule is the result of a genetic experiment because it is a cross between a male horse and a female donkey it cannot reproduce though because of the difference in the chromosomes or something it gets rather technical so I won't really explain it. In the case of Clark I think the alien origin thing plays a part, but it would raise the question as to why he was sent to Earth in the first place.
