In Sigmund Freud’s account of human nature, incest plays a leading role. In brief, we have incestuous desires but these are normally blocked or displaced in some way, be it via castrating fathers, the moral codes of the societies in which we live, or the psychological tricks we play on ourselves. And while most anthropologists have distanced themselves from Freud, they have often followed him in giving incest a leading role in their own accounts of what it is to be human. Lévi-Strauss, building on Mauss, said that incest taboos – found everywhere – are what compel men to exchange gifts and make alliances. They need each other’s sisters because they are everywhere banned from procreating with their own.

Then again, it might be said that procreating with one’s own sister (or brother) is just about the last thing on anybody’s mind, and that even without a taboo it wouldn’t happen often. The anthropologist and philosopher Edward Westermarck suspected as much. Surely most people find the thought of close kin incest very off-putting. This reaction could be a function of cultural learning, i.e. the public condemnation of incest might be what turns us against it. A very different possibility, however, and the one that Westermarck argued for, is that we are naturally against it. But if he was right about this we’re left with a puzzle: why do human societies bother to condemn something that nobody wants in the first place? Arthur Wolf’s short and engaging book, which takes a firm Westermarckian line, attempts to explain both the fact that we have a natural aversion to incest and the fact that we (nevertheless) go to a lot of trouble to ban it.

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Meanwhile, the edited volume by Naomi Quinn and Jeannette Mageo has its own Freudian backstory. The “Western theory” of their subtitle is the highly influential attachment theory of the British psychologist John Bowlby. Although trained in the Freudian tradition, Bowlby increasingly distanced himself from it, and in particular its stress on infant and child sexuality. What infants and children desire from their caregivers, Bowlby argued, is care rather than sex. More specifically, what they really want are secure relations of attachment – which explains why they become so visibly anxious at moments of unwanted separation from caregivers.

Crucially, both Bowlby’s theory (that we naturally crave attachment) and Westermarck’s theory (that we naturally abhor incest) have an evolutionary basis, something bound to set off alarm bells for many social and cultural anthropologists. What is incontestable, however, is that human infants are highly dependent creatures and that this period of dependency lasts a long time. We have thus been selected by evolutionary pressures, Bowlby argues, for “good” attachment behaviours, i.e. because on average this helps us to survive. But if abandonment presents one kind of risk to human survival, incest presents another: over time it has very bad consequences for the fitness of our descendants. We as a species have thus been selected, Westermarck argues, to have the disposition, under normal circumstances, not to desire it at all.

Arthur Wolf is a universalist, by which I just mean that he believes in such a thing as human nature. Thus it is that he agrees with Westermarck that humans have a natural aversion to incest and that this has an evolutionary basis. But he is still left with the question of why we have incest taboos, and the question of why these should vary so much between cultures, as they clearly do. His book is basically an attempt to take a universalist theory and show how it can help us make sense of all the cultural variation we find out there in the real world. By contrast, the edited book by Quinn and Mageo is framed around a more familiar anthropological narrative. They use the cultural variation we find out there in the real world to suggest that Bowlby’s universalist attachment theory is fatally flawed and that it should never have become so influential in the first place.

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As readers of Wolf’s earlier work on incest aversion will know, his interest in this topic was prompted by an encounter, as a young anthropologist, with an unusual marriage practice. In the Taiwanese village where he first conducted fieldwork, it happened that a significant proportion of older women had been married under what are known as “little daughter-in-law” arrangements. They had been adopted (often as infants) with the understanding that eventually they would marry one of the sons of their adoptive parents. They thus normally grew up alongside their future husbands, in many cases starting from early infancy. Why such arrangements? For one thing, it allowed families to avoid the sometimes crippling cost of “buying” fully grown up brides for their sons later on. For another thing, a daughter-in-law raised in her future in-laws’ home was felt by many to be a better proposition – less risky – than one who had been raised by her own parents and who might remain under their influence.

However, there was one major flaw in this logic: the marriages themselves didn’t function very well. When Wolf later used demographic data to explore this in forensic detail – as explained in his masterful Sexual attraction and childhood association – he discovered that “little daughter in law” marriages had strikingly low rates of fertility and strikingly high rates of adultery and divorce. In short, Wolf concludes, the men and women who were expected to live with these arrangements often found it hard going where sex was concerned. The source of the problem, as Westermarck had predicted, was the prolonged period of “childhood association” between future spouses – early childhood co-residence being, in evolutionary terms, a good proxy for close kin connection. In this marriage form, then, everything happened as if people were marrying their siblings and committing incest – even though, in fact, they were not marrying their siblings, and even though this form of marriage was not considered incestuous at all (it was culturally sanctioned, and quite wide-spread).

Taken on its own, Wolf’s Taiwanese case study doesn’t prove that Westermarck’s theory about incest aversion is right. But it’s an important case because, as Wolf has stressed over the years, it gives us a good (indeed, singular) opportunity to put the theory to a direct test. It is also backed up by converging evidence from other cases, as well as data about incest aversion in other species. And yet none of this really gets to the second half of the problem. If humans have a natural aversion to incest, why do we also ban it? Couldn’t we just let nature take its course? What sets this short book apart from Wolf’s previous writings on the subject is his attempt to grapple seriously with the second half of the problem. Notably, in doing so he distinguishes himself from scholars such as the sociobiologist E.O. Wilson who believe, as he does, that incest avoidance is natural. The mistake of these scholars, according to Wolf, is to treat incest taboos as if they were simply “an aspect of incest avoidance”, i.e. to assume that the former are just cultural elaborations of the latter (p 67). Wolf, being an anthropologist, can’t accept this, and in the second half of the book he shifts firmly onto ethnographic ground – citing Schapera, Kluckhohn, Firth, Bloch and many others – in an attempt to make sense of his complicated subject matter.

I will not spell out Wolf’s argument in detail here (he provides his own useful summary at the end of the book). But he starts, logically, from the Westermarckian point that most people don’t have incestuous desires in the first place: they’ve evolved not to. This means that close kin incest is in fact rare in human societies. When this rare thing does happen, however, it is startling and it tends to be feared. In particular – and here Wolf draws on wide-ranging ethnographic evidence – it is thought likely to presage a “collective calamity” for society as a whole. It must thus be banned. But if the story were to end there, we might find little variation in incest taboos across cultures, whereas of course we find a lot of it. Why? The simple answer is history. Our evolved incest aversion relates to close kin incest. But over time our rules about incest (which in any case are a reaction to the rarity of incest as opposed to being just an amplification of our aversion to it) have come to be applied much more widely, including to categories of persons who – in biological terms – have no meaningful kin connection whatever. Variation in incest taboos is thus, in part, a product of historical variation in kinship systems. A closely related point is that in the course of history incest taboos have often become political phenomena. They are ripe for manipulation – including via the institutions of kinship – precisely because of the powerful hold that incest, an unexpected and indeed near-inexplicable phenomenon, has on the human imagination.

Readers of this book should, I think, bear in mind that the second half of it is rather unlike the first half, and not only in terms of the basic questions that the two halves set out to tackle. The overall narrative of the book is seamless and Wolf is a powerful writer. But the first half (about incest aversion) is ultimately focused on a highly particular, and in fact relatively narrow, hypothesis – about the consequences of childhood association for sexual desire or its absence – and on the testing of this in the few places where it can be properly tested. Fortunately, there’s compelling evidence out there (not only in Taiwan) that bears directly on the hypothesis. You don’t have to agree with Wolf’s conclusions, and not everyone does, but at least it’s very clear what kind of case he wants to make and also on what basis. The second half of the book (on incest taboos) is framed around a more complicated theory, one that basically unfolds in steps; in Wolf’s own summary, there are 12 of these (starting with two that emerge from the earlier chapters). The core evidence base in support of these steps is also significantly more complex and, in many respects, more subject to interpretation than that deployed in the first half of the book. Showing that Taiwanese “little daughter in law” marriages have low fertility rates is one thing: if you can prove it demographically then there may not be much room for argument. Showing that humans are fearful of rare events, and thus see incest as intrinsically threatening to the social order, is quite another proposition. To be clear: Wolf does cite a good deal of psychological and ethnographic evidence in support of his arguments. The question is whether this evidence is compelling enough and, more especially, whether – when linked together in a series of steps – it can support the causal claims that Wolf would like to make on the basis of it. This question matters because if there’s one thing that Arthur Wolf has – very usefully – hammered home in his life’s work it is that we as anthropologists should think very hard (and much harder than we normally do) about how different types of evidence may or may not support the different types of scientific claims that we want to make.

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If Arthur Wolf could be said to be exasperated by the lack of respect given to Westermarck by anthropologists, Naomi Quinn and Jeannette Mageo could be said to be exasperated in a different direction: they can’t believe how influential John Bowlby’s theory of attachment remains among psychologists in spite of attacks on it over a period of decades, not least by anthropologists. Bowlby’s evolutionary argument, to say it again, is that humans have evolved to care about attachment to caregivers and thus about separation from them. During childhood, he went on to reason, if our experiences of separation – e.g. from our mothers – are not too traumatic we learn to live with it and become more (healthily) independent in the process. But if our experiences are very bad ones – say, because of negligent mothering – this may leave a deep imprint on our psychology. Forming secure and stable attachments with others later in life may prove difficult.

A crucial point in the history of this theory is that attachment behaviours are observable phenomena. In particular, one can easily watch and record how infants/children actually do react when their carers leave them alone. In case you haven’t noticed, they sometimes go ballistic. But is such behaviour universal? The simple answer is no. As anthropologists and cultural psychologists have long shown, culturally variable arrangements have many consequences for child development, including in relation to attachment. What, for example, if care giving from birth is invested in a lot of people rather than just in the mother? In that case, a child doesn’t have a single attachment figure and the “problem” of separation should presumably become more diffuse (and, one might think, more manageable). Another question is how the behaviours of infants/children – in connection to separation or anything else – come to be interpreted by observers. In the classic Bowlbian framework, developed with his colleague Mary Ainsworth, a child who reacts coldly rather than emotionally to separation is labeled as “avoidant”: which is basically bad news. In one well-known study, almost exactly half of all children in a German community fell into that problematic category. As Robert LeVine and Karin Norman showed, however, this was the product of enculturation. So far as their German parents were concerned, it was a good thing if their young children were independent and non-clingy. The parents were thus actually pleased by evidence that, from the attachment theory point of view, should have worried them a lot.

This book builds on and considerably expands these (already well-established) challenges to attachment theory, but it also seeks to take them further and – at least in the introductory chapter by the two editors – to expand them into a general critique of psychology. In the end, Quinn & Mageo argue, psychology in general, and not only attachment theory, is pervaded by ethnocentrism. It has all kinds of Western (and sometimes specifically American) assumptions built into it, and thus cannot legitimately claim to be the science of human psychology in general.

Of course, many anthropologists love to hear just this kind of message, but there is a sting in the tail for them. In fact, the contributors to this volume are not committed relativists. Although they believe (mostly on ethnographic grounds) that attachment theory is flawed – and perhaps even more so the standard methods for studying attachment and for classifying behavioural evidence about it – they do not think that there is no such thing as attachment that could be studied across human cultures. On the contrary, a number of the chapters in this book are embedded in an evolutionary framework that assumes – as did Bowlby – that humans have evolved to care about proximity to their caregivers and other important figures in their lives. The authors of these chapters, at least, are seeking to integrate this (by definition) universal fact with the undeniable reality of cultural variation on the ground, including in the care provided to infants and children. More broadly, the contributors to this book share something else with Arthur Wolf, i.e. beyond a shared interest in evolution: they are not afraid to talk about, and actually engage directly with, questions of human psychology. Anthropologists who are wary of “psychologism”, in whatever stripe, might thus wish to avoid the book. But if they read this edited collection about attachment across cultures – and/or Arthur Wolf’s book about incest aversion and culturally variable incest taboos – they will actually learn a lot about what it is to be human.