Some would argue that humans have innate values, common between all societies. In most, if not all, societies on Earth, murder is considered wrong or taboo, for instance. This would seem to imply that certain ethics and morals are "brute."
However, the same could be said for many other ethics that we would consider constant laws. In some places, without concepts of ownership, there would be nothing unethical about downloading or sharing music for free. In places with little concepts of time, there would be nothing rude about keeping another waiting in anticipation of a meeting (a diplomatic disaster, for sure.) In places where women far outnumber men, there would be nothing taboo about taking multiple wives, or vise versa.
And even in societies where these practices are unacceptable, people who practice them rarely feel that they are doing something wrong until they are caught. When someone cuts you off on the interstate, you shake your fist and say how it pisses you off. But when YOU cut someone else off, it's justified, because you were in a hurry. "I'm not a bad person," you reason, "I was justified in my actions, because I had good reason to do it." In light of this, one could conclude that ethics and morals are institutional.
Personally, I believe that laws and ethics are like all other things... impermanent. At times they may be brute, and at other times they may be institutional, and at still other times they may not exist at all. The waves crash endlessly upon the shores, the moon waxes and it wanes. So it is with everything, given time.
"There is nothing you can see that is not a flower, nothing you can think of that is not the moon." ~Bashio