It's easy to see why it's a problem when we look into the past. Presumably, every creature should be considered to the be the same species as its parents. But g

It's easy to see why it's a problem when we look into the past. Presumably, every creature should be considered to the be the same species as its parents. But go far enough back and your N-great grandparents are undeniably a different species. If we had a record of every organism that had ever lived, trying to classify them into "species" would be a ridiculous task -- regardless of how punctuated-equilibriumy things are. Since the fossil record is fairly spotty, it's only a slightly ridiculous task.