What implications could scientific knowledge about ourselves have for moral conduct or social policy? No number of factual statements about human nature, by themselves, can ever entail statements that amount to moral knowledge, as Hume demonstrated. What is required is an ethical theory, persuasive on other grounds, that already links "is" and "ought". This might be found, for example, in a definition of moral action in terms of human flourishing, though it is not clear why we should, as individuals, be concerned about something as abstract as that - why not merely the flourishing of ourselves or our particular loved ones?
One comfort is that, even if we had a plausible set of empirical and meta-ethical gadgets to connect what we know of human nature to high-level questions about social policy, we would discover significant slippage between levels. Nature does not contradict itself, and no findings from a field such as evolutionary psychology could be inconsistent with the observed facts of cultural diversity. If reductive explanations of human nature become available in more detail, they must turn out to be compatible with the existence of the vast spectrum of viable cultures that human beings have created so far.
The dark side of evolutionary psychology includes, among other things, some scary-looking claims about the reproductive and sociopolitical behaviour of the respective sexes. True, no one seriously asserts that sexual conduct in human societies and the respective roles of men and women within families and extra-familial hierarchies are specified by our genes in a direct or detailed fashion. What, however, are we to make of the controversial analyses of male and female reproductive "strategies" that have been popularised by several writers in the 1990s? E.g., some accounts argue that men are genetically hardwired to be highly polygamous or promiscuous, while women are similarly programmed to be imperfectly monogamous, as well as sexually deceitful.
In responding to this, first, I am in favour of scrutinising the evidence for such claims very carefully, since they can so readily be adapted to support out-worn stereotypes about the roles of the sexes. That, however, is a reason to show scientific and philosophical rigour, not to accept strong social constructionism about science. Secondly, even if something like this turned out to be correct, the social consequences of such knowledge are by no means apparent. Mere biological facts cannot tell us in some absolute way what are the correct sexual mores for a human society.
To take this a step further, theories about reproductive strategies suggest that there are in-built conflicts between the interests of men and women, and of higher and lower status men, which will inevitably need to be moderated by social compromise, not necessarily in the same way by different cultures. If all this were accepted for the sake of argument, it might destroy a precious notion about ourselves: that there is a simple way for relations between the sexes to be harmonious. On the other hand, it would seem to support rather than refute what might be considered a "progressive" notion: that no one society, certainly not our own, has the absolutely final answer to questions about sexual morality.
Although evolutionary psychology and cognitive neuroscience are potential minefields, it is irrational to pretend that they are incapable of discovering objective knowledge. Fortunately, such knowledge will surely include insight into the slippage between our genetic similarity and the diversity of forms taken by viable cultures. The commonality of human nature will be at a level that is consistent with the (substantial) historical contingency of social practices and of many areas of understanding and evaluative belief. The effect on social policy is likely to be limited, though we may become more charitable about what moral requirements are reasonable for the kinds of creatures that we are.
I should add that evolutionary psychology and cognitive neuroscience are not about to put the humanities, in particular, out of business. At this stage, there is a banality in attempts to produce illuminating comment about the arts, based on evolutionary considerations. There are good reasons why the natural sciences cannot provide a substitute for humanistic explanation, even if we obtain a far deeper understanding of our own genetic and neurophysiological make-up. This is partly because reductive science is ill-equipped to deal with the particularity of complex events, partly because causal explanation may not be all that we want, anyway, when we try to interpret and clarify human experience.
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Let's just make that last point more vivid. There may, I suppose, be some ultimate set of incredibly complex physical facts on which supervenes a higher-level fact such as "Macbeth is a tragic hero" or "Macbeth is the main character in
Macbeth" or "
Macbeth deals, thematically, with the perils of ambition" or even the factual content of a complex claim that somehow relates the thematic concerns of
Macbeth to its recurrent imagery. (I remember once discussing something like this with Greg Egan, but not in a way that makes Greg someone who disagrees with the thrust of this post - I think his example was understanding the Battle of Waterloo.)
But despite the previous paragraph, we can make all these humanistic claims without relying on any processes that are distinctively scientific, and even if we had a super-science that could, in principle, explain how all these claims are true, assuming they are, it would be impossible to deploy the super-science in particular cases. There is just no substitute for a sensitivity to language, including to how the English language has changed over the centuries, and that requires the sort of study that goes on within the arts and humanities. If we were talking about a play written in a foreign language, there would be no real substitute for a sensitive mastery of that other language, even if we could "get" quite a lot from a good translation. Moreover, there is also no substitute for a sensitivity to literary forms and historical contexts.
When we encounter particular complex cultural products, such as the play
Macbeth - perhaps we wish to discuss the play as a text, or to discuss a particular production of it, or even the performance of a particular actor playing one of the well-known characters - a scientific education won't be especially helpful, and distinctively scientific techniques will seldom be of much use.
That's not to say they can never be of any use at all to students of the humanities - I can think of examples where they may well be - but these techniques are not going to put the humanities as we know them out of business.