BROTHER-SISTER INCEST IN THE ANTHROPOLOGICAL RECORD
On the Westermarck Effect and other theories about Incest Avoidance
What lessons, in conclusion, may be derived from the recent efforts to understand the incest taboo/avoidance? One is the sobering reflection that an alleged universal that has exercised the anthropological imagination for over 100 years is still not explained to everyone's satisfaction. It is not even certain that the phenomenon is a universal.
- Donald E. Brown, Human Universals (1991)
Hey Folks,
Incest in a hot topic in anthropology. This isn’t because anthropologists are a bunch of perverts. It’s an important subject.
Okay, maybe it’s partly because anthropologists are a bunch of perverts. But it really is important, I swear.
Every society, including stateless societies, has some kind of social contract. This includes a set of understandings about what constitutes right and wrong. There is enormous variation between different cultures about what exactly that social contract looks like, but there is no society in which anything goes.
I originally got into studying anthropology because, as an anarchist, I wanted to learn about stateless societies. One of the things that I quickly realized is that stateless societies govern themselves not through laws but through custom and taboo, which are in turn mediated through their culture’s Mythos, which is transmitted through art and rituals.
With this understanding, I came to see taboo as a subject of vital importance in understanding human societies. They are an inalienable part of every culture’s social contract. And you can’t get far into studying taboo without studying sexual taboos.
One of the most primal layers of any society’s social contract pertains to who is allowed to fuck whom, and under what circumstances.
In some societies, homosexuality is extremely common. In others, it is seen as so harmful that it may be punishable by death. In still others, it is apparently unthinkable - when anthropologists have questioned members of certain indigenous societies about gay sex, they have concluded that it had never occurred to their informants that such a thing were possible.
Some societies consider extramarital sex perfectly normal, whereas in others it is seen as a threat to the very fabric of society.
Historically, most societies have practiced some form of cousin marriage, but over the last 200 years a strong taboo against it has spread across the world.
I could go on and on and on.
Most non-anthropologists believe that there is such a thing as “The Incest Taboo”, and that exists cross-culturally. This is sort of true, but not quite. It is true that every single society has taboos related to incest, but those taboos vary tremendously.
Case in point: the Piraha.
According to the anthropologist Daniel Everett, who lived among the small Amazonian tribe over the course of 30 years, the Piraha have no prohibition against marriage between half-siblings.
In his classic ethnography of the Piraha, he writes:
Anthropologists have long believed that the more complex the kinship system, the more likely it is that there will be kinship-based restrictions on whom to marry, which relative to live close to or with, and so on. But the inverse necessarily holds as well—the fewer the number of kinship terms, the smaller the number of kinship-related restrictions there will be in a society.
This has an interesting effect in Piraha. Since they lack any word for cousin, unsurprisingly there is no restriction against marrying a cousin. And, perhaps because [the kinship term] xahaigi is ambiguous, I have even seen men marry their half sisters. The effect of the apparently universal incest taboo prohibits only a small number of sexual couplings among the Pirahas, such as full sibling with full sibling and grandparent or parent with child.
Everett does not mention any harmful effects of this inbreeding.
Now, it should be mentioned that cultures which allow marriage between siblings (or half-siblings) are exceedingly rare in the anthropological record. But they aren’t unheard of.
The best evidence that exists for a culture in which sibling marriage was widespread comes from Egypt.
Approximately 44 years after Alexander the Great conquered Egypt in 332 BCE, a Greek king of Egypt divorced his wife and married his full sister, who was about ten years older than he. While there may have been some Greek precedent for his action—half-sibling marriages were alleged to be possible in certain ancient Greek communities—he was also following an ancient Egyptian custom. Whatever the case, seven of the next eleven Greek kings in Egypt married their sisters. There is some vague evidence that the custom was penetrating other parts of the populace. Egypt subsequently passed to Roman rule.
Beginning in 19–20 CE and lasting until 257–258 CE, the Roman administrators of Egypt conducted periodic censuses of the Egyptian population. Some 270 actual household returns survive; 172 returns, listing 880 persons, are in good enough condition to be used. Seventeen of the 113 marriages ongoing at the time of the censuses were definitely between brother and sister; another six may have been. Thus, some 15 to 21 percent of the ongoing marriages reported in these returns were brother-sister marriages. Eleven or twelve marriages were between full siblings, eight between half-siblings; in three cases, the kind of sibling relationship is uncertain.
Given the probable demographic structure of the family under the conditions of the time, there was only about a 40 percent likelihood of any family having a brother and sister of marriageable age. Thus, a third or more of those who could marry their sisters did so. This is a very high proportion and, if correct, it provides the only known case in which brother-sister marriages were common throughout a populace.
Perplexingly, history does not attest to a higher incidence of birth defects or child mortality caused by inbreeding. And multiple academic studies have carefully scrutinized the evidence.
For example, in 1980 a scholar named Keith Hopkins wrote a paper called Brother-Sister Marriage in Roman Egypt. In it, he fails to find any evidence that the widespread practice of sibling marriage led to a rise in birth defects or increased child mortality. He reasons that such effects might have been masked by an already-high baseline rate of child mortality.
This brings us to the question - do the injurious effects of in-breeding explain incest taboos? How much do we really know about birth defects caused by in-breeding?
According to Donald E. Brown:
Reviewing the scanty literature on the empirical consequences of in-breeding among humans, Shepher (1983) finds that full-sibling or parent-child incest results in about 17 percent child mortality and 25 percent child disability, for a combined result of about 42 percent nonviable offspring. The negative consequences decline rapidly for more distant inbreeding. If the figures Shepher cites are even approximately correct, mechanisms to avoid the costs of incest between close kin are quite expectable.
In other words, the incest taboo exists to prevent in-breeding because in-breeding is evolutionarily maladaptive. Simple, right?
Strangely, it would seem not. Not everyone accepts that conclusions can be drawn based on the available evidence. Apparently it just isn’t robust enough, which in itself seems strange.
To my mind, this raises the question: why is the literature on in-breeding “scanty”? Shouldn’t this matter have been solved long ago?
We all feel like we know that in-breeding leads to birth defects. But how do we “know”? Do we “know” because of firsthand knowledge - because we know people who have had kids with their siblings? Do we “know” because of secondhand knowledge - because we have heard accounts from people who know people who have had kids with their siblings? Or we just “know” because “everybody knows”?
Perhaps we have been to certain areas where there seems like there is something a little off about the locals, and we wonder whether it might be due to in-breeding. If that is the source of our “knowledge”, however, we may do well to reconsider it.
Personally, I consider it extremely probable that there is some connection between incest avoidance and the avoidance of birth defects. It’s the simplest explanation, and it makes the most intuitive sense.
But surprisingly, there is no agreement amongst anthropologists about incest taboos after more than 150 years of serious scholarly debate. Weird, eh?
Many anthropologists favour more complicated cultural explanations for the near-universality of incest taboos. For example, in The Elementary Structures of Kinship, Claude Levi-Strauss promoted the idea that incest taboos exist to promote social harmony by encouraging exogamy (marriage outside the group). This is surely true in some cases, but it seems inadequate to explain the near-universality of incest taboos.
Anyway, what I’m about to share is an excerpt from a book called Human Universals by Donald E. Brown. It is a concise summary of different theories about incest avoidance.
Human Universals was published in 1991, but as far as I’m aware, it still represents the consensus (or lack thereof) of anthropologists so far as incest taboos are concerned.
Enjoy!
Crow Qu’appelle
Incest Avoidance
by Donald E. Brown, excerpted from Human Universals (1991)
The apparent universality, or near-universality, of the incest taboo perennially fascinates anthropologists and has given rise to numerous speculations about its origin and function. The principal point of agreement is probably that incest is in some way harmful, so that avoiding it confers some benefit. What the harm, what the benefit, and how the taboo or avoidance comes about are points of contention.
Progress in understanding the whole issue has been retarded by several false starts and misconceptions (summarized in Fox 1980, Arens 1986). For example, there has been a tendency to conflate marriage rules with sexual regulations. While these concerns may impinge on one another—and might very well be equated in the folk categories of a given people—there is no necessary connection between them: incest fundamentally concerns sex; only coincidentally may it concern marriage.
There was also an assumption that animals—unlike humans—do mate incestuously, so that the human prohibition of incest was a distinctively cultural marker of humanity’s separation from the animal world. It is now known that incest is rare among animals in the wild (domestic animals, whose breeding patterns have been altered by human interference, are another matter). Between human incest avoidance and the patterns of behavior among other animals there may thus be a continuity that was previously denied.
As a corollary of the assumption that the incest taboo was a distinctively cultural invention—that would leave no obvious material remains in the archaeological record—the actual origins of the taboo, being lost in antiquity, were not subject to empirical research. Indeed, most discussion of the incest taboo was little more than a sideline to other issues.
Another assumption now known to be wrong was that the incest taboo was universal. But in a number of societies, royalty were enjoined to commit incest (or, at any rate, to marry very close kin). And in some societies, there are no obvious incest taboos in the sense of rules (and sanctioned rules especially) against it, only a notion that no one would commit incest anyway.
Finally, the various relationships in which incest might occur—e.g., between brother and sister, or between father and daughter—tended to be all run together.
The present chapter is primarily about brother-sister incest, and a recent line of research conducted primarily by anthropologists to test an idea formulated in the last century—but long ignored—that it is human nature for brothers and sisters to avoid incest. This line of research moved an old anthropological subject out of the realm of speculation into the realm of concrete and comparative studies.
One of the leading controversies has turned fundamentally around an issue of human psychology: is incest tabooed because we naturally tend to commit it but shouldn't, or is it tabooed, somewhat paradoxically, because most humans don’t want to do it? The former position was championed by Freud and others, who could see no reason why a taboo should exist for something we didn’t want to do anyway. The latter position was expounded late in the nineteenth century by a Finnish anthropologist, Edward Westermarck, who argued that there is "a remarkable lack of erotic feeling between persons who have been living closely together from childhood" (1922:192). Such persons, he noted, would typically be relatives. Incest avoidance, thus, was a natural tendency that resulted from childhood association. Westermarck’s reply to the objection Freud raised was that incest was tabooed for the same reason bestiality and parricide are tabooed: not because we have a general tendency to commit them but because some individuals go awry in ways that shock general sentiments. The rules are for them.
Unlike most (if not all other) anthropologists, Westermarck was centrally concerned with the incest taboo and its implications, and he wrote...
Unlike most (if not all) other anthropologists, Westermarck was centrally concerned with the incest taboo and its implications, writing extensively on the matter over decades. He took a straightforward Darwinian view: inbreeding was directly harmful, and the avoidance resulting from childhood association was an evolved human instinct. Despite his extraordinary efforts to understand the incest taboo, his views were largely eclipsed by anthropology's opposition to biological reductionism through World War II, as they "violated... every canon" of anthropology (Murdock 1932:209).
However, in the 1950s, J.R. (Robin) Fox (1962) recognized that social experiments conducted in Israel provided remarkable evidence bearing on incest avoidance between siblings. The ensuing revival of Westermarck's ideas led to most of the studies summarized below.
In Israeli kibbutzim—communal villages first founded early in the twentieth century—there was a deliberate attempt to break down the nuclear family. Boys and girls close in age were raised together in peer groups (kvutza) of six to eight children, sharing common living quarters from shortly after birth through adolescence. Under the care of nurses and teachers rather than parents, the children shared an intimate association and underwent common socialization and education. As small children, they exhibited typical sexual interest in each other, but this interest disappeared as they matured. Although they were free to marry one another, provided they were not actual siblings, Spiro (1958) found not a single case of this happening, nor even of sexual intercourse between children raised together from childhood in the same peer group.
Fox (1962) observed that the kibbutz data supported Westermarck's hypothesis but believed Freud was at least partly correct as well. In Fox's reformulation, the close and literal physical intimacy of children socialized together renders them sexually uninterested in each other after puberty. Among Freud's patients, however, most siblings were not raised with the physical intimacy common in the kibbutz, leading them to harbor sexual desires for each other.
According to Fox, societies with kibbutz-like child-rearing patterns are likely to be relatively indifferent to incest; they disapprove but generally do not stringently punish it, as most members have no significant interest in it. Societies with child-rearing patterns more akin to those of Freud's patients are more likely to have stringent taboos, as their members need the taboo to overcome real desires to commit incest. Fox summarized the pattern: "the intensity of heterosexual attraction between co-socialized children after puberty is inversely proportionate to the intensity of heterosexual activity between them before puberty" (1962:147). He illustrated this with examples from the Tallensi of Ghana, the Pondo of Southeast Africa, the Mountain Arapesh of New Guinea, the Tikopia, and a Chinese situation described below, which fit the kibbutz pattern. In contrast, the Chiricahua Apache and the Trobriand Islanders fit the pattern described by Freud.
A study based on three additional Israeli communes indicated that the Westermarck effect, as Fox termed it, was not confined to the commune Spiro had studied (Talmon 1964). Whether based on Israeli or other data, most studies of incest avoidance from the mid-1960s onward have focused specifically on Westermarck's position, with Fox's defense of a modified Freudian position receiving little attention (but see Willner 1983 and Spain 1987).
A Chinese practice, described by Arthur Wolf (1966, 1968, 1970) and Wolf and Huang (1980), provided another natural experiment supporting Westermarck. In many areas of China, there were until recently two forms of marriage: "major" and "minor." In the minor form, a young girl was adopted into the family of her future husband. The motivation for this arrangement stemmed from the serious strain between daughters-in-law and mothers-in-law in Chinese society. By bringing the future daughter-in-law in as a very young child, she could adjust and more readily subordinate herself to her mother-in-law long before becoming a bride. The future husband and wife were unrelated, so there was no violation of the incest taboo. However, the boy and his future bride were raised under conditions typical of siblings—sharing the intimacy of the family.
These minor marriages often resulted in higher divorce rates and fewer children compared to major marriages. Wolf's analysis suggested that the sibling-like upbringing led to a lack of sexual attraction between the couples, supporting the Westermarck hypothesis.3
Arthur Wolf's research challenges Freud's assertion that familial intimacy fosters sexual interests necessitating suppression via the incest taboo. Supporting Westermarck's hypothesis, Wolf found that "minor marriages"—arranged unions where a girl is adopted into her future husband's family during childhood—were approximately 30% less fertile and notably unhappier. Men in such marriages more frequently sought extramarital relationships, including visiting prostitutes and taking mistresses; their wives also engaged in extramarital affairs more often. These marriages had higher rates of separation and divorce. These objective indicators corroborate Chinese observations that spouses in minor marriages found each other less romantically or erotically appealing. As economic changes diminished parental authority to enforce minor-marriage arrangements, couples increasingly made alternative arrangements, spontaneously avoiding such unions.
Wolf also highlighted a study on sibling incest in Chicago by Weinberg (1963), which found that only siblings raised apart contemplated marriage with each other. Wolf's conclusions have faced criticism, often through alternative interpretations of the same data. For instance, some suggest that the lower prestige of minor marriages leads to poorer treatment of the bride, resulting in marital dissatisfaction. However, Wolf and Huang (1980:173–175) noted that brides in regular (major) marriages often faced more mistreatment upon moving into their in-laws' households. They also demonstrated that couples in even less prestigious arrangements—where the groom joins the bride's family—experienced more fertile and stable marriages than those in minor marriages (1980:169, 185). Interestingly, Wolf and Huang (1980:285) reported that their Chinese informants seemed unaware of the reduced fertility associated with minor marriages.
Further support for the Westermarck hypothesis comes from the Near East. In Arab societies, there's a noted preference for a man to marry his father's brother's daughter—a close relative in patrilineal kinship systems. While such marriages are more common than in other regions, they are not predominant. Given that brothers often live in close proximity, their children grow up together, making the preference for such unions seemingly counter to the Westermarck hypothesis. However, Justine McCabe (1983), studying an Arab village in Lebanon, found evidence supporting Westermarck's theory.
In McCabe's study, "first cousins grew up in an association as close as that of siblings" (1983:58). The relationship between a boy and his father's brother's daughter mirrored that of siblings: characterized by constant and intimate interaction from birth, including early sexual exploration, and marked by "informality, candor, teasing, tattling, quarreling, laughing, joking," and sharing confidences (1983:59). Marriages between patrilateral parallel cousins produced 23% fewer children over the first 25 years and were four times more likely to end in divorce compared to other marriages. McCabe (1983:61) cites other scholars who, early in the 20th century, noted signs of greater "sexual apathy" or "coolness" in such marriages. As in the Chinese case, McCabe argues that it's parents or others, not the marrying individuals, who prefer patrilateral parallel cousin marriages.
If the Westermarck effect is genuine, determining the age limits for its development is crucial. Wolf and Huang (1980:185) observed that minor marriages where children were brought together before age 4 were twice as likely to end in divorce compared to those where children became acquainted at age 8 or later. Joseph Shepher (1983), born and raised in an Israeli commune, conducted an extensive study on marriage in Israeli kibbutzim, analyzing data from 2,769 married couples across 211 kibbutzim. He found only 20 marriages between members of the same commune and just 14 between individuals who had been in the same peer group. Upon contacting these 14 couples, all had dissolved their marriages: there wasn't a single case of marriage between a boy and girl who had spent their first six years in the same peer group. In his own commune, where reliable data on premarital sex were available, he found no instances of such activity between individuals raised together from infancy. However, boys and girls introduced to the group at later ages sometimes developed intense attractions to group mates.
There was no attempt in the communes to prevent sexual experimentation among young children or to restrict adolescents and young adults from dating or marrying their commune mates, although they were generally expected to abstain from sex during high school. In fact, intracommunal marriages were somewhat encouraged. By examining patterns of entry and exit from peer groups and the resulting attractions or lack thereof, Shepher concluded that a form of imprinting (or negative imprinting) occurred, completed by age 6 and taking approximately four years. He argued that this imprinting is a phylogenetic adaptation to mitigate the harmful effects of inbreeding.
Research outside anthropology also bears on the Westermarck hypothesis. Studies on the physical and medical consequences of inbreeding among humans and other animals, evolved inbreeding avoidance mechanisms in nonhuman species, and the social consequences of human incest are pertinent. Reviewing limited literature on the empirical consequences of human inbreeding, Shepher (1983) found that full-sibling or parent-child incest results in about 17% child mortality and 25% child disability, culminating in approximately 42% nonviable offspring. These negative consequences decline rapidly with more distant inbreeding. If Shepher's figures are even approximately correct, mechanisms to avoid the costs of incest between close kin are quite plausible.
A study of 38 captive mammalian species found an average of around 33% offspring mortality resulting from closely incestuous matings, with nonviability ranging from 0 to nearly 100% (Ralls, Ballou, and Templeton 1988). Consequently, widespread mechanisms have evolved among animals to avoid incest, operating through prohibition (notably among humans), prevention, and inhibition (Shepher 1983). Prevention entails circumstances where incest cannot occur, such as parents dying before offspring reach fertility or siblings being widely dispersed. Inhibition, potentially resulting from imprinting or related processes, occurs when closely related and fertile individuals in proximity avoid mating. Wolf, McCabe, and Shepher provide evidence for a form of negative imprinting that typically inhibits brother-sister incest among humans. Although evidence is minimal, Shepher (1983:108–110) suggests that mother-son incest is also inhibited by imprinting, given the prolonged and intimate mother-child contact. In many societies, opportunities for developing aversion between father and child are less prevalent.
Incest avoidance through prevention or inhibition mechanisms is widely reported among many animal species (Bischof 1972), making parent-offspring or sibling incest among wild animals relatively rare (Lewin 1989:482). Thus, the notion that human incest avoidance is purely cultural rests on the unlikely assumption of a double discontinuity with the animal kingdom: unlike other species, humans lack innate avoidance mechanisms and instead rely solely on cultural prohibitions (Arens 1986:94).
Another research avenue, primarily pursued by psychologists and sociologists in recent decades, focuses on actual cases of human incest—a topic previously neglected in anthropological discourse. One significant outcome of these studies is the challenge to the sociological or functionalist explanation of the incest taboo. Historically, figures like Jeremy Bentham and various anthropologists posited that incestuous relations would disrupt family organization, rendering it inefficient and, by extension, society as a whole. However, empirical studies have not substantiated this claim.
Bagley (1969), as summarized in Arens (1986), analyzed 425 published incest cases, identifying 93 instances where incest served to maintain family functionality. Typically, a father-daughter relationship supplanted the father-mother relationship when the mother was unable or unwilling to fulfill her role—a phenomenon Bagley termed "functional incest." Regardless of the psychological costs to individuals, these studies provide no clear evidence that incest necessarily threatens societal or familial structures (Arens 1986; see also Willner 1983 and La Fontaine 1988).
A recent study by Parker and Parker (1986) offers more direct insights into the Westermarck hypothesis. While the exact frequencies of various nuclear family incest forms—brother-sister, mother-son, father-daughter—remain uncertain, there's consensus that father-daughter incest is more prevalent than mother-son incest. Notably, stepfather-stepdaughter incest appears disproportionately common. Several explanations exist, including the role of imprinting: if imprinting inhibits incestuous desires, it would likely be most effective between mother and son, less so between father and daughter, and even less between stepfather and stepdaughter.
Parker and Parker (1986) compared sexually abusive and non-abusive fathers with similar backgrounds. Among fathers present during their daughters' first three years, abusers were "much less frequently involved in caring and nurturing activities" (1986:540). They also found that stepfathers or adoptive fathers were more likely to be abusive, possibly due to a lack of effective bonding (imprinting) experiences. When comparing biological fathers to step or adoptive fathers with similar early childhood contact levels, no significant differences in abuse rates emerged (1986:541). These findings support and extend the Westermarck hypothesis beyond the brother-sister dynamic, the primary focus of recent anthropological studies.
Despite mounting evidence supporting the Westermarck hypothesis and undermining alternatives like the functionalist perspective, debates persist. Ancient Egyptian practices, for instance, present challenges where evidence for the Westermarck effect seems strongest: inhibition of brother-sister incest. Keith Hopkins (1980) provides evidence that brother-sister marriages were common in Egypt during certain periods, suggesting that incest avoidance may not be universal.
Approximately 44 years after Alexander the Great's conquest of Egypt in 332 B.C., a Greek king of Egypt divorced his wife to marry his full sister, following an ancient Egyptian custom. Subsequently, 7 of the next 11 Greek kings in Egypt married their sisters. Evidence suggests this practice extended beyond royalty. Roman administrators of Egypt conducted censuses between A.D. 19–20 and 257–
Wolf found, contrary to Freud and others who argue that familial intimacy is the breeding ground of sexual interests that must be thwarted by the incest taboo, and in support of Westermarck, that minor marriages were about 30 percent less fertile and were unhappier. Men in such marriages resorted to prostitutes, took mistresses, or sought extramarital affairs more frequently; their wives engaged in extramarital affairs more frequently; and such marriages more frequently resulted in separation or divorce. These objective indices buttressed Chinese statements to the effect that husband and wife in minor marriages found each other less romantically or erotically attractive. When various economic developments eroded parental ability to enforce minor-marriage arrangements, the couples who were to marry in this manner made other arrangements, spontaneously avoiding the minor marriages.
Wolf also drew attention to a study of sibling incest in Chicago (Weinberg 1963). It found that the only offenders who had contemplated marriage with each other were those who had been raised apart. Wolf's conclusions have been criticized, generally by offering alternative interpretations of the same data. For example, it has been suggested that because the minor marriage is less prestigious, the bride in such a marriage will be treated poorly and hence make a poor wife, or the couple in such a marriage will be chagrined by the stigma of it and thus make a poor marriage. But Wolf and Huang (1980:173-175) point out that regular (major-marriage) brides are more mistreated when they move into their in-laws’ household, and they show that couples brought together in a marriage that is clearly less prestigious than minor marriage—one in which the groom goes to live with the bride's family—have more fertile and more stable marriages than the minor marriages (1980:169, 185).
Interestingly, Wolf and Huang (1980:285) report that their Chinese informants seemed unaware of the lesser fertility of minor marriages.
Further support for the Westermarck hypothesis comes from the Near East. Students of Arab societies have long been aware of a preference often found among those peoples for a man to marry his father's brother’s daughter, who, given the patrilineal nature of their kinship system, is a rather close relative by any sense of the term. Marriages that conform to this ideal are not in fact very common, though more common than in other parts of the world. Since brothers typically live in close social and spatial contact with each other in Arab societies, it follows that their children are likely to be close too and, hence, that the preference for them to marry appears to run counter to the Westermarck hypothesis. However, Justine McCabe (1983), who studied an Arab village in Lebanon, found that the evidence supports Westermarck.
However, Justine McCabe (1983), studying a Lebanese village, found otherwise.
In the village McCabe studied, “first cousins grew up in an association as close as that of siblings” (1983:58). She found that the relationship between a boy and his father's brother's daughter was essentially the same as between a boy and his sister: it rested on a constant and intimate interaction from birth (including sexual exploration when very young), and was characterized by “informality, candor, teasing, tattling, quarreling, laughing, joking” and the exchange of confidences (1983:59). But marriages between patrilateral parallel cousins produced 23 percent fewer children during the first 25 years of marriage and were four times more likely to end in divorce than all other marriages. McCabe (1983:61) cites other scholars who, from early in this century, had noted signs of greater “sexual apathy” or “coolness” in patrilateral cousin marriages. As in the Chinese case, McCabe argues, it is parents or others, not the ones who actually marry, who prefer patrilateral parallel cousin marriages.
If the Westermarck effect is real, an important issue is the age limits within which it is created. Wolf and Huang (1980:185) offered some insight into the matter by noting that minor marriages in which the children were brought together before age 4 were two times more likely to end in divorce than minor marriages in which the children became acquainted at age 8 or later. Joseph Shepher (1983) has looked at the matter more closely. Born and raised in an Israeli commune himself, Shepher conducted the most thorough study of marriage in Israeli communes, getting data on 2,769 married couples in 211 kibbutzim. Among them he found only 20 marriages between members of the same commune and only 14 that allegedly took place between persons who had been in the same peer group. But on contacting these 14 couples he found that all cases dissolved: there was not a single case of marriage between a boy and girl who had spent the first 6 years of their lives in the same peer group. In the one commune (his own) in which he could get reliable data on premarital sex he also found that none had occurred between persons raised from infancy in the same peer group. Boys and girls brought into the group at later ages sometimes did have an intense attraction to one of their group mates.
There was no attempt in the communes to stop the sexual experimentation of young children. There was no attempt to keep adolescents and young adults from dating or marrying their commune mates, though they were supposed to refrain from sex in general during high school. There was in fact some encouragement of intracommunal marriage. Examining the pattern of entry and exit from peer groups, and the resulting pattern of attraction or sexual interest or uninterest among the relevant parties, Shepher concludes that a form of imprinting (or negative imprinting) occurred, that it was complete by the age of 6, and that it took about 4 years. He argues that this imprinting is a phylogenetic adaptation to reduce the harmful effects of inbreeding.
Certain lines of research conducted largely outside of anthropology also have a close bearing on the Westermarck hypothesis. They include studies of the physical or medical consequences of inbreeding among humans (as well as other animals), studies of evolved inbreeding avoidance mechanisms in nonhuman species, and studies of the social consequences of human incest.
Reviewing the scanty literature on the empirical consequences of in- breeding among humans, Shepher (1983) finds that full-sibling or parent-child incest results in about 17 percent child mortality and 25 percent child disability, for a combined result of about 42 percent nonviable offspring. The negative consequences decline rapidly for more distant inbreeding. If the figures Shepher cites are even approximately correct, mechanisms to avoid the costs of incest between close kin are quite expectable.1
Arens (1986:17–23; see also May 1979) summarizes the same or similar materials, with similar results (but cf. Bittles 1983). Arens wonders how, if the consequences of inbreeding are “not controversial or debatable,” it is then possible for some anthropologists to consider inbreeding costs irrelevant to understanding incest avoidance (1986:21). The answers are that by taking populations (not individuals) as units of analysis, some anthropologists have (1) noted that populations would not necessarily suffer from inbreeding, while others (2) observe that sustained inbreeding would, over the generations, actually eliminate harmful genes from the gene pool. Each of these lines of thought ignores “the immediate disadvantages for those most immediately involved” (Arens 1986:23).
A study of 38 captive mammalian species found a cross-species average of around 33 percent offspring mortality resulting from closely incestuous matings (the range of nonviability—measured rather conservatively in terms of “juvenile survival”—was all the way from 0 to nearly 100 percent) (Ralls, Ballou, and Templeton 1988). As the apparent consequence of this widespread phenomenon, equally widespread mechanisms have evolved that enable animals to avoid incest. These mechanisms operate in three distinguishable ways: by prohibition (only among humans, of course), by prevention, and by inhibition (Shepher 1983). In the case of prevention, incest simply cannot occur (because, for example, parents die before their offspring become fertile, or siblings are so widely dispersed that there is minuscule likelihood of their mating). Inhibition, apparently brought about by imprinting or related processes, occurs when closely related and fertile individuals are in proximity but avoid mating with each other. Wolf, McCabe, and Shepher all provide evidence for some kind of negative imprinting that would, in the normal course of events, inhibit brother-sister incest among humans. Although the evidence he presents is minimal, Shepher (1983:108–110) argues that mother-son incest is also inhibited by imprinting (see also Fox 1980, Arens 1986). The opportunity for their imprinting is of course excellent, due to the prolonged and intimate contact of mother and child. In a great many societies the opportunities for developing aversion between father and child are the least.
Incest avoidance, via mechanisms of prevention or inhibition, is widely reported among many animal species (Bischof 1972), so that parent-offspring or sibling incest among animals in the wild is “apparently rather rare” (Lewin 1989:482). Consequently, the assumption that human incest avoidance is fundamentally a cultural phenomenon now rests on the inelegant assumption of a double discontinuity with the animal kingdom: unlike other species we lack innate avoidance mechanisms; unlike other species we therefore avoid incest via cultural prohibition (Arens 1986:94).
A third line of research, conducted mostly by psychologists and sociologists, and mostly in recent decades, concerns actual cases of human incest—a topic curiously neglected during most of the period in which the incest taboo has exercised the anthropological imagination. One of the most important consequences of these studies is their dismissal of the sociological or functionalist explanation of the incest taboo. In a line of thought that Arens (1986:29) traces back as far as Jeremy Bentham—but in more recent times through many distinguished anthropologists—it has often been argued that incestuous relations would confound the organization of the family, rendering it inefficient and thereby rendering society inefficient. As persuasive as this line of reasoning has been—in the absence of empirical tests—it now appears to be incorrect.
Bagley (1969; summarized in Arens 1986) analyzed 425 published cases of incest, finding 93 instances in which incest was the means that allowed the family to maintain its functional integrity. Typically, a father-daughter relationship replaced the father-mother relationship when the mother was either unable or unwilling to fulfill her role. Bagley (1969) describes this as “functional incest.” Whatever the psychological costs may be to individuals, the study of actual cases of incest gives no obvious support to the assumption that society, or even the family, is necessarily threatened by incest (Arens 1986; see also Willner 1983 and La Fontaine 1988).
A recent study (Parker and Parker 1986) of incestuous relationships has a more direct bearing on the Westermarck hypothesis. Although the actual frequencies of the various forms of nuclear family incest—brother-sister, mother-son, and father-daughter—are a matter of uncertainty, there is substantial agreement that father-daughter incest is much commoner than mother-son incest. Furthermore, the variant of stepfather-stepdaughter incest seems to be disproportionately common. There are a number of explanations for this, not all of them mutually exclusive. One of them has to do with imprinting: if some form of imprinting results in the inhibition of incestuous desires, on the average it would, as noted earlier, probably work best between mother and son, not so well between father and daughter, and even less well between stepfather and stepdaughter.
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Parker and Parker (1986) tested this line of thought by comparing sexually abusive and nonabusive fathers with comparable backgrounds. Comparing fathers who had been present in the household during the first three years of their daughters’ lives, the Parkers found that abusers had been “much less frequently involved in caring and nurturing activities” (1986:540). They also found that in general stepfathers or adoptive fathers were more likely to be abusive, apparently because such fathers were less likely to have an effective bonding (imprinting) experience. When biological fathers were compared to step- or adoptive fathers with similar degrees of early childhood contacts with their daughters, no significant differences in abuse were found (1986:541). These findings support the Westermarck hypothesis and extend it beyond the brother-sister relationship that has been the principal focus of recent anthropological studies.
But in spite of the mounting evidence that supports the Westermarck hypothesis and fails to support its rivals, such as the functionalist hypothesis, the dust has not settled on all the issues involved. Ancient Egyptian materials, for example, pose a problem precisely where the evidence for the Westermarck effect seems strongest: inhibition of brother-sister incest. Keith Hopkins (1980) provides evidence that brother-sister marriages were actually common for a period in Egypt and, hence, that incest avoidance in general, not merely the taboo, may not in fact be universal.
About 44 years after Alexander the Great conquered Egypt in 332 B.C. a Greek king of Egypt divorced his wife and married his full sister (who was about 10 years older than he). While there may have been some Greek precedent for his action—half-sibling marriages were alleged to be possible in certain ancient Greek communities—he was also following an ancient Egyptian custom. Whatever the case, 7 of the next 11 Greek kings in Egypt married their sisters. There is some vague evidence that the custom was penetrating other parts of the populace. Egypt subsequently passed to Roman rule.
Beginning in A.D. 19-20 and lasting until 257-258, the Roman administrators of Egypt conducted periodic censuses of the Egyptian population. Some 270 actual household returns survive; 172 returns, listing 880 persons, are in good enough condition to be used. While not in any sense a random sample, they report households widely spread in time, space, and social class. Seventeen of the 113 marriages ongoing at the time of the censuses were definitely between brother and sister, another 6 may have been. Thus some 15 to 21 percent of the ongoing marriages reported in these returns were brother-sister marriages. Eleven or 12 marriages were between full siblings, 8 between half siblings; in 3 the kind of sibling relationship is uncertain. Given the probable demographic structure of the family under the conditions of the time, there was only about a 40 percent likelihood of any family having a brother and sister of marriageable age. Thus a third or more of those who could marry their sisters did so. This is a very high proportion and, if correct, it provides the only known case in which brother-sister marriages were common throughout a populace.
Other forms of documentation—such as wedding invitations, letters, and marriage contracts—routinely mention brother-sister marriage, which indicates not only that it occurred but that it was considered normal. Some letters indicate real affection between the sibling couples, although this line of evidence is weakened by the Egyptian use of the term “sister” as a euphemism or term of endearment for women who were not actually one’s sister (Arens 1986:111–112).
The marriages were fertile, and no source indicates an awareness of harmful genetic consequences. But Hopkins does not indicate how fertile they were, and perhaps it should be asked whether the high rates of infant mortality in preindustrial societies might not tend to mask any mortality brought about by inbreeding (recall also that the Chinese seemed unaware of the lesser fertility of their minor marriages).
Hopkins is unable to find any reason peculiar to the Egyptian condition that may have induced parents to foist this kind of marriage on their children (though the late average age of first marriages—in their mid-twenties—does suggest parental involvement). Hopkins cites marriage contracts between brothers and sisters that specify dowry and/or separate property and hence suggest that sibling marriage was not a device to avoid marriage expenses or the division of family property.
Addressing the problem of how else to explain brother-sister marriage, Hopkins presents what can only be called a classically cultural explanation. He draws attention to the importance in Egyptian religion of Isis and Osiris, who were brother and sister, husband and wife; a romantic tradition of idealizing brother-sister love in story and poetry; and the evidence that the status of women was high and that they therefore exercised some autonomy in marriage and divorce. That love was a basis for marriage, and its cessation a basis for divorce, is well attested. Hence, Hopkins is left with the possibility that brothers and sisters married because they wanted to.
In A.D. 212-213 the Egyptians were made Roman citizens, for whom marriage with near-kin was prohibited. Sibling marriage disappeared.
Given the spottiness of the Egyptian data it is difficult to decide how much credence to give them. But a few points should be noted. Hopkins gives the ages of five sibling couples; they were separated in age by 7, 8, 4, 8, and 20 years. With one exception, then, these are not necessarily couples who were raised together as children or, at any rate, who were raised together in the manner that produces the Westermarck effect. It would be of interest to know more about child-rearing practices among Roman Egyptians.
Shepher’s (1983) response to the Egyptian case was to dismiss it on the grounds that the data were few and that a single exception can carry little weight (he thereby reversed, by the way, the de facto opinion of many anthropologists that a single exception is all it takes to dismiss claims of universality). In this context, Shepher argued that unrestricted universals were not very likely to occur anyway—since nature operates by probability—so that a near-universal was the most to be expected.
Spiro (1982) summarizes other criticisms of the Westermarck hypothesis and adds his own. He notes, for example, an alternative interpretation of the kibbutz case. Spiro says it is not the child rearing but rather the adolescent repression of sexuality that produces the strong tendency for boys and girls to go outside their peer group and kibbutz to find mates. In adolescence, children were still living together, but their childhood exploration of sexuality was to stop. They were strongly urged to forgo sex until education was complete. In Spiro’s view, this adolescent frustration resulted in peer group members’ lack of interest in one another— they responded, in effect, to a consciously stated taboo.
To support his argument, Spiro cites Kaffman (1977), a psychiatrist employed by the kibbutz movement, who says that liaisons between children raised in the same peer group do in fact now occur. Since infant socialization has not changed, but adolescent controls have been relaxed, it is adolescent conditions that are critical. Unfortunately, Kaffman gives no data. Shepher (1983) dismisses Kaffman’s argument and notes that marriages between those who had been adolescent (but not childhood) peers did occur before; hence, adolescent repression of sexuality could not have been the crucial factor. (But note that such marriages weren't at all common. A defect in Shepher’s contribution is that by narrowing imprinting to a 4-year period that must occur in the first 6 years of life he has made this a small part of what must be various controls on incest, since even individuals who were not reared in the same peer group but who were resident in the same commune seem to marry rather infrequently. The low rate of intra-kibbutz marriage in general must find some of its explanation in some other factors.)
Spiro also draws attention to two further considerations. One is the smallness of the peer groups, which makes finding a mate outside them statistically expectable. The other is that the boys and girls in the peer groups were the same age; since young girls tend to be interested in older boys, and older boys in younger girls, they therefore tend to seek mates outside the peer group.
What lessons, in conclusion, may be derived from the recent efforts to understand the incest taboo/avoidance? One is the sobering reflection that an alleged universal that has exercised the anthropological imagination for over 100 years is still not explained to everyone's satisfaction. It is not even certain that the phenomenon is a universal. The incest taboo clearly is not universal, though it surely is a statistical universal and might be a near-universal. On the other hand, incest avoidance may be universal.
Even more sobering has been the impact of biological considerations that for decades were all but banned from mainstream anthropological thought. The ethological discovery that humans are far from unique in avoiding incest has entirely reoriented the problem. The resuscitation of the Westermarck hypothesis has provided a successfully tested explanation for part of the phenomenon. In eliminating possible hypotheses, and in accumulating relevant data, then, there has been progress. This experience suggests that anthropologists might do well to look into other lines of thought that may have been neglected for no good reason (a lesson no less applicable to sociology; see Scheff 1985).
Also important to notice in the incest-avoidance example is the clear attempt to explain the phenomenon by clarifying the ultimate (evolutionary) conditions that generate the mechanisms and by specifying the proximate mechanisms that generate the universal—infant (negative) imprinting, resulting in specified psychological states in the individual. Equally important has been the exploitation of natural experiments and the role that quantitative testing or analysis has played.
In the long run it may be that the Westermarck hypothesis will not stand up; certainly it is only a partial explanation that does not preclude other, complementary explanations. But the mode of explaining—involving ethological and evolutionary perspectives, a detailed specification of mechanisms and of individual motivation, a diligent search for natural experiments, and quantitative tests when possible—deserves emulation with other universals.
Arens (1986:17—23; see also May 1979) summarizes the same or similar materials, with similar results (but cf. Bittles 1983). Arens wonders how, if the consequences of inbreeding are “not controversial or debatable,” it is then possible for some anthropologists to consider inbreeding costs irrelevant to understanding incest avoidance (1986-21). The answers are that by taking populations (not individuals) as units of analysis, some anthropologists have (1) noted that populations would not necessarily suffer from inbreeding, while others (2) observe that sustained inbreeding would, over the generations, actually eliminate harmful genes from the gene pool. Each of these lines of thought ignores “the immediate disadvantages for those most immediately involved” (Arens 1986-23).
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