The mighty PhysOrg site has an entry up about a paper in PLoS analyzing the evolution of specialization in cells. If you feel up to it, read the full paper here. Sergey Gavrilets at the University of Tennessee at Knoxville did a million-generation computer simulation to study how cells might become specialized in multicellular organisms, even if the specific cells "want" to maximize their own success. ("Want" is in scare quotes because, of course, cells don't consciously desire anything, but in this context it's a useful shorthand expression.) In other words, how do cells -- which are mindless -- nevertheless "decide" to cooperate and rely on each other?
Apparently it took a relatively short time -- a million generations, but for cells a "generation" can be a matter of hours -- for the cells to evolve specialized functions within a larger colony. The cells (and remember, these are very simplified mathematical simulations, not real organisms) which form colonies and do their part for its survival ultimately have more daughter cells than the ones which cheat and maximize their own survival.
In short, ethics is a winning evolutionary strategy even at the cellular level. And Adam Smith's division of labor is also more efficient at the cellular level than a war of all against all. At least, that's what the math suggests.