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Why not marry your cousin? Millions do

The topic of consanguineous marriage raises both interest and unease in Western societies. For those who are wondering, that big word means “marrying your cousin”. But why would anyone want to marry a…

American singer Jerry Lee Lewis famously married his cousin. flickr/dunechaser

The topic of consanguineous marriage raises both interest and unease in Western societies. For those who are wondering, that big word means “marrying your cousin”.

But why would anyone want to marry a cousin when there are so many other potential partners out there?

In generational terms this mode of thought is actually quite recent, and until the middle of the 19th century first cousin marriage was common in most Western countries, in part due to the shortage of available unrelated spouses in many outlying areas.

The times they are a'changin

The public mood in Europe and North America gradually changed, with a growing belief that marriages between couples who were close kin would result in unfavourable health outcomes for their offspring.

In the USA this reversal in attitude resulted in the introduction of state-based legislation to restrict or even ban marriages between first cousins.

Apart from 31 of the 50 US states, only China, Taiwan, the Koreas and The Philippines have introduced similar civil restrictions on first cousin unions, although regulations that curtail cousin marriage apply to members of the Roman Catholic and Orthodox churches.

Good law or prejudice?

Are these proscriptions justified, and if so why do they not apply to the rest of the world’s population, where a conservatively estimated 1100+ million people are married to a spouse who is a second cousin or closer, or are the offspring of such a marriage?

And what is the actual basis for our suspicion of consanguinity – is it primarily founded on religious, social or genetic grounds, and why has there been a recent upsurge in calls for a ban on first cousin marriage by politicians in many European countries?

These topics form the basis of my recent book Consanguinity in Context. As a geneticist I have been researching the health aspects of consanguineous marriage for over 30 years in South and Southeast Asia, the Middle East and North Africa, among migrant communities in Australia and the UK, and as adviser to the World Health Organization.

You won’t have children with webbed toes … really

Perhaps surprisingly to many, the genetic risks which have been associated with cousin marriage have been substantially overstated.

While some families and communities are indeed more likely to be affected by otherwise rare inherited diseases, a large majority of first cousin offspring show no disadvantage in health terms.

Further, many of the ill-effects on health that have been ascribed to “inbreeding” are more probably due to a wide range of adverse non-genetic factors, including young maternal age, very short birth intervals, trans-placental infection of the developing fetus with organisms such as rubella and cytomegalovirus, and inadequate nutrition both during pregnancy and early childhood.

In assessing whether or not consanguinity is “good” or “bad” there has been a notable failure to take into account the social and economic benefits of close kin marriage, which is a particularly important consideration in the poorer sections of societies where consanguinity is more common. Or to acknowledge that wives in consanguineous unions generally seem to enjoy more equal status.

Inevitable challenge

Given the entrenched opinions that the topic of cousin marriage often attracts, it is probable that these opinions will be challenged. But that is the nature of science, and I have undertaken extensive research to support the conclusions drawn.

The reality is that cousin marriage is something health planners and the general public will need to come to terms with in Australia’s multi-ethnic society.

It is not an issue we are accustomed to dealing with as a society, but once we remove historical prejudice, we find that consanguineous marriage is not the backwoods horror story we have been led to believe.

Which may perhaps provide some solace for those who have long harboured a secret crush on a cousin.

It also could add some spice to those dreary family get togethers.

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