in the previous post on tribes and types of cousin marriages, i posted a couple of graphics illustrating father’s brother’s daughter (fbd) marriage and mother’s brother’s daughter (mbd) marriage, showing how fbd marriage is a closed system while mbd marriage enables alliances with other lineages/clans.
here now are the last two forms of cousin marriage: father’s sister’s daughter (fzd) marriage and mother’s sister’s daughter (mzd) marriage. they’re not very different from the other two — fbd and fzd marriage are both closed systems, and mbd and mzd marriage both enable alliances with other lineages/clans — it’s just that the connections are slightly different, i.e. ego marries the daughter of his one of his aunts (fzd & mzd) versus his one of his uncles (fbd & mbd).
note that the coefficients of relatedness in cousin marriage are highest for mzd marriage; next highest for mbd marriage; and lowest for both fbd and fzd, which are the same (if i’ve done my maths right!). mbd marriage is the most common form of cousin marriage around the world; fbd marriage is the most common in arab countries and places like iran, afghanistan and pakistan.
here we go. father’s sister’s daughter (fzd) marriage over several generations (triangles are boys, circles are girls. compare with fbd marriage):
and mother’s sister’s daughter (mzd) marriage over several generations (compare with mbd marriage):
the thing with either mbd or mzd marriage is that the bride is always being brought in from an outside lineage or clan. fbd and fzd marriage is diametrically the opposite — the bride is from the same patrilineage as ego.
also, in mbd and mzd marriage, in each generation a bride can be brought in from a different lineage or clan, so ego’s lineage can build up many alliances with many other lineages/clans over time. some societies apparently have, traditionally, had arrangements in which several lineages would swap brides over several generations in a cyclical system, thus building up extended familial connections and, therefore, alliances. i imagine that very large tribes could be built up this way, whereas the fbd/fzd system results in segmented lineages, i.e. clans and sub-clans and sub-sub-clans that always seem to be squabbling.
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