its not their brain. its in their genes, their DNA. If it's in the genes (both parents) then it doesn't explain the fact of a person that is a genius when neither parent is. I have a girlfriend who has 3 children all in their mid-30s now, and all are bright individuals, but her one son is a genius and has made a great deal of money because of it. As my girlfriend says "I have no idea where he got THAT from!" I don't believe it's a "throw-back" to ancestors or you would have heard of it by now. I think it's simply unexplainable.