Deepika probably there is something wrong with the development of homo sapiens sapiens. You can say  Nature has chosen some horribly wrong trait s in the bio logical cauldron of the froth to speak like common English and certain traits which were a part of say , have you read cell physiology : there is a mechanism of vacuole , this vacuole contains dissolving solutions, this is a highly complex mechanism of cell physiology. It has plethora of functions. I can not write a phd for you over here as its really a phd topic which I have happened to write. But this mechanism if understood on psychiatric know how an intrinsic sadistic trait is what that come off. I hope you can understand now.