Well, somewhat notoriously, there has been a rolling debate for better than a century now over whether "higher" sciences simply are complex subdiciplines of "lower" sciences. E.g., are all biologists ultimately just physicists? How about psychologists? Economists? The proper meaning of "are" itself in that sentence also, rightly, is the subject of significant dispute. But the analogy isn't the best since I think that philosophers enjoy that question a lot more than actual scientists.
A more interesting example may be law and economics. There has been a concerted movement by certain economists/legal theorists to show either that law is simply applied (or misapplied) economics, or that it should be. (Here's a taste: http://www.law.berkeley.edu/faculty/cooterr/PDFpapers/stratc...) Again, though, the analogy is imperfect. I don't think that many would claim that law "is" economics, but rather that legal rules are or should be explicable in strictly economic terms. Though maybe this would satisfy some definitions of "is."
