This talk of mixing science and morality prompts suspicion in some quarters: just because something is "natural" doesn't mean it is "right", in an ethical sense, and efforts to derive codes of moral conduct from science rarely end well. (Sam Harris's recent book, The Moral Landscape: how science can determine human values, is one such car crash: all it really shows is how science could be used to help construct Harris's version of a perfect society, which isn't the same point at all.) Moreover, it is unclear what Zak means when he says oxytocin, or the lack of it, "makes" us good or evil. This is the same problem as with news reports about scientists discovering the part of the brain "responsible for" risk-taking, or greed, or a belief in God: just because you have found the biological underpinnings of some phenomenon, it does not necessarily follow that you have found "the real cause" of it. Still, none of that undermines the most potent aspect of Zak's work, which is the pragmatic one. If oxytocin is the mechanism through which moral action takes place, that holds out the possibility - a cause of either optimism or alarm, depending on how you look at it - that by manipulating oxytocin, we might boost the levels of trust, generosity, and ultimately happiness in ourselves and the world at large.