I ran across this image attached to a rather vitriolic post (the thrust of which was, in essence, “only stupid inbred hicks oppose gay marriage and this map proves it”), but it struck something of a thought process. Here goes.
First of all, the map’s not entirely accurate with respect to what the author was trying to say. Five states, at least, shouldn’t be listed as “allowing” cousin marriage, since their restrictions make it so that an impossibly small portion of their population will realistically participate. There’s a considerable overlap with gay and cousin marriage allowability in the northeastern section of the US. And of course the Granola State on the west coast, a place which carries almost entirely the opposite of the “inbred hick” stereotype, allows cousin marriage and has gone back and forth on the issue of gay marriage for a few years now.
Secondly, the science against cousin marriage is muddled. The usual argument put against it is that it encourages genetic diseases. In certain populations, specifically populations where cousin marriage is encouraged and founder effects come into play, this is true. Small, isolated rural villages of current/past ages, the inbred lines of European royalty, and the lines of fundamentalist Mormonism come to mind here. Another example is the Dutch settlers to South Africa (the “Afrikaners”), who carry magnified risk of Huntington’s Disease because an abnormal percentage of the original settlers were carriers.
On the other hand, research into larger, more diverse genetic populations indicates that “once in a while” cousin marriage carries relatively small risk - about the same risk as a woman having kids at the age of 40 rather than 30. The further argument is that laws against it in the US were motivated not by risk of genetic disease, but by a desire to force immigrants to intermarry into the population (and thus assimilate) in a quicker manner.
Oddly enough, the argument about “inbred hicks” falls apart when comparing the map of European gay marriage laws. I’d put a map up comparing it to European laws about cousin marriage, but there’s no real point to it: cousin marriage is legal in 100% of Europe. Two countries have recently begun discussing the option of banning it, and oddly enough, it’s not even the condition of their oddly buckteethed/colorblind/hemophiliac (that last being the origin of the term “blue-blood” as a reference to royalty) royal lines that did it, but rather the high rate of genetic diseases in recent immigrant populations from the rural sectors of Islamic countries, who perpetuate societal cousin marriage rates of 55% or above in a population where it’s not uncommon to be the child of a chain of 8-10 cousin marriages (including “double cousin” marriages, wherein the kids are not simply cousins but where mother/aunt and father/uncle, or mother/uncle and father/aunt, constitute sibling pairs as well making the kids almost genetic siblings) in a row.
The trouble with this is discussion that it’s a perfect example of a “where do we draw the line” sort of argument. On the one hand, in a (mostly healthy) genetic population where cousin marriage would be rare and genetic diversity a given, arguers against cousin marriage would quickly expire upon the line of “well why do we let 40-year-old women have kids then?” On the other hand, we have definitive proof of the genetic risks of allowing multigenerational cousin marriage. There even comes the risk that at some point, society could start stopping non-sibling people from marrying because they both carried a recessive gene for some debilitating genetic disease like Huntington’s or Tay-Sachs, or even something as merely inconvenient as Celiac. It’s not that farfetched; some states to this day still require a blood test, a holdover from times when they were screening for sexually transmitted diseases such as syphilis. Another justification (now that the technology exists) for genetic testing as a marriage requirement could be to ensure that they aren’t unknowingly marrying their half-sibling or even full sibling, due to the high percentage of absentee/unknown fathers or potential for siblings to be separated too early in life to remember each other in certain populations.