In any discussion of , or human sciences in general, it is very important to avoid two logical fallacies. They are called the naturalistic fallacy and the moralistic fallacy.

The naturalistic fallacy, which was coined by the English philosopher George Edward Moore in the early 20th century though first identified much earlier by the Scottish philosopher David Hume, is the leap from is to ought – that is, the tendency to believe that what is natural is good; that what is, ought to be. For example, one might commit the error of the naturalist fallacy and say, “Because people are genetically different and endowed with different innate abilities and talents, they ought to be treated differently.”

The moralistic fallacy, coined by the Harvard microbiologist Bernard Davis in the 1970s, is the opposite of the naturalistic fallacy. It refers to the leap from ought to is, the claim that the way things should be is the way they are. This is the tendency to believe that what is good is natural; that what ought to be, is. For example, one might commit the error of the moralistic fallacy and say, “Because everybody ought to be treated equally, there are no innate genetic differences between people.” The science writer extraordinaire Matt Ridley calls it the reverse naturalistic fallacy.

Both are logical fallacies, and they get in the way of progress in science in general, and in evolutionary psychology in particular. However, as Ridley astutely points out, political conservatives are more likely to commit the naturalistic fallacy (“Nature designed men to be competitive and women to be nurturing, so women ought to stay home to take care of the children and leave to men”), while political liberals are equally likely to commit the moralistic fallacy (“The Western liberal democratic principles hold that men and women ought to be treated equally under the law, and therefore men and women are biologically identical and any study that demonstrates otherwise is a priori false”).

Since academics, and social scientists in particular, are overwhelmingly left-wing liberals, the moralistic fallacy has been a much greater problem in academic discussions of evolutionary psychology than the naturalistic fallacy. Most academics are above committing the naturalistic fallacy, but they are not above committing the moralistic fallacy. The social scientists’ stubborn refusal to accept and race differences in behavior, temperament, and cognitive abilities, and their tendency to be blind to the empirical reality of stereotypes, reflect their moralistic fallacy driven by their liberal political convictions.

It is actually very easy to avoid both fallacies – both leaps of logic – by simply never talking about what ought to be at all and only talking about what is. It is not possible to make either the naturalistic or the moralistic fallacy if scientists never talk about ought. Scientists – real scientists – do not draw moral conclusions and implications from the empirical observations they make, and they are not guided in their observations by moral and political principles. Real scientists only care about what is, and do not at all care about what ought to be.

There are only two legitimate criteria by which to evaluate scientific ideas and theories: logic and evidence. Accordingly, you may justifiably criticize evolutionary psychological theories (or any other theories in science) if they are logically inconsistent within themselves or if there is credible scientific evidence against them. As a scientist, as the scientific fundamentalist, I take all such criticisms seriously. However, you cannot criticize scientific theories, whether mine or otherwise, simply because their implications are immoral, ugly, contrary to our ideals, or offensive to some or all. As regular readers of this blog already know very well by now, the implications of many of the scientific ideas and theories, whether mine or otherwise, are indeed immoral, ugly, contrary to our ideals, or offensive either to men or women (or some other groups of people). I simply do not care. If what I say is wrong (because it is illogical or lacks credible scientific evidence), then it is my problem. If what I say offends you, it is your problem.

Truth is the only guiding principle in science, and it is the most important thing for all scientists. In fact, it is the only important thing; nothing else matters in science besides the truth. However, I also believe that any solution to a social problem must start with the correct assessment of the problem itself and its possible causes. We can never devise a correct solution to a problem if we don’t know what its ultimate causes are. So the true observations are important foundations of both basic science and social policy, if you do care about solving social problems, which of course I don’t.