Damnit, I hate that claim. Here's a great article on why gay marriage should, and will, be legalized eventually...
Gay Marriage and Anthropology
Linda S Stone
Washington State U
Politicians and the public in the US today are raising a question once pursued by anthropologists in the 1950s, namely, what should we mean by marriage? The politically charged issue concerns whether or not a constitutional definition of marriage can exclude same-sex couples. With over a century of experience in the study of kinship and marriage worldwide, anthropology can offer perspectives on this debate that may be of interest to our students or the general public.
Can Marriage Be Defined?
Many politicians claim that those advocating gay and lesbian marriage are trying to redefine marriage. But what anthropologists have learned is that from a global, cross-cultural perspective, “marriage” is in the first place extremely difficult, some would say impossible, to define. One anthropologist, Edmund Leach tried to define marriage in his 1955 article “Polyandry, Inheritance and the Definition of Marriage” published in MAN. Leach quickly gave up this task, concluding that no definition could cover all the varied institutions that anthropologists regularly consider as marriage. Rejecting Leach’s conclusion, Kathleen Gough attempted to define marriage cross-culturally in 1959 as an institution conferring full “birth status rights” to children (The Nayars and the Definition of Marriage. Royal Anthropological Institute of Great Britain and Ireland 89:23-34). Gough’s definition of marriage was convoluted—notable, in her own words, for its “inevitably clumsy phraseology”—since it covered monogamy, polygyny, polyandry and same-sex marriage. But most important, its core feature—conferring of birth status rights on children—does not hold up cross-culturally.
It is true that virtually every society in the world has an institution that is very tempting to label as “marriage,” but these institutions simply do not share common characteristics. Marriage in most societies establishes the legitimacy or status rights of children, but this is not the case, for example, among the Navajo where children born to a woman, married or not, become full legitimate members of her matriclan and suffer no disadvantages. “Marriage” around the world most often involves heterosexual unions, but there are important exceptions to this. There are cases of legitimate same-sex marriages as, for example, woman-woman marriage among the Nuer and some other African groups. Here, a barren woman divorces her husband, takes another woman as her wife, and arranges for a surrogate to impregnate this woman. Any children from this arrangement become members of the barren woman’s natal patrilineage and refer to the barren woman as their father. Among some Native American groups, males who preferred to live as women (berdache) adopted the names and clothing of women and often became wives of other men.
Marriage usually involves sexual relationships between spouses. Yet this was not true of Nuer woman-woman marriages and we find in European history cases of “celibate marriages” among early Christians. Often spouses are co-resident but very often this is not the case. A separate residence of husbands in “men’s houses,” away from their wives and children, has been common in many places. Among the polyandrous/polygynous Nayar of India, wives and husbands remained in their own natal groups with husbands periodically “visiting” their wives and with children raised by their mothers and mothers’ brothers. Indeed the only feature of marriages that is apparently universal is that they will create affinal (in-law) relationships, or alliances, a fact that Lévi-Strauss and others considered to lie behind the origin of human marriage. But even here, affinal relationships are themselves quite varied in their nature and importance across societies. Thus, in terms of child legitimacy, sex of spouses, sexual activity, residence and so on, what we see around the world in terms of marriage is most notable for its variation.
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http://www.aaanet.org/press/an/0405if-comm4.htm