is an elephant capable of breeding or reproducing with a rat ? 
 if yes, why yes and if no, then why no... 
 support your answer.  i know its funny, but i still need to clear my doubt...please explain with more examples of animals.
the one thing i have learned, having traveled thus far, is to never say "never".  i would tend to say no, since there is quite a large size difference between the elephant and the rat.  the reproductive machinery would have to be compatible, so that is the first stumbling block to producing a successful cross.  history is full, however, of animals that have similar, but different lineage, being successfully mated together to produce hybrid offspring.  probably the earliest example is the breeding of a female horse with a male donkey to produce a mule.  practically all the known breeds of dogs are the result of selective breeding, where breeders would cross this breed with that breed to produce an offspring with characteristics of each.   the liger is a cross between a male lion and a female tiger.  a yakalo is a cross between a male yak and a female buffalo.  so as you can see, there has to be some compatibility between the two animals to get the desired results to come about.