Intra-familial marriage examined in major new book

April 23, 2012

A comprehensive account of intra-familial marriage, its genetic effects and common misconceptions has been written by a Murdoch University researcher.

Adjunct Professor Alan Bittles from Murdoch’s Centre for Comparative Genomics has spent 35 years researching the effect of consanguineous (or same blood) marriages on health outcomes and intellectual and development disabilities.

In Consanguinity in Context, which will be published by Cambridge University Press on May 7, Prof Bittles provides an overview of the topic and critical analyses of the influence of consanguinity on health.

“There are more than 1100 million people worldwide who are married to a close relative or are the offspring of such a marriage, living in regions where 20 to 50 per cent of marriages are between blood relatives, so these types of marital unions are in no way rare,” said Prof Bittles.

“They are common in many Muslim, Buddhist, Christian, Hindu and Jewish communities and migration means their incidence is on the rise in many Western cultures including Australia, the UK and the United States.

“The general belief is that first cousin marriages lead to negative genetic outcomes, yet a large majority of children born to first cousins are healthy. A global analysis has shown that early death or major ill-health is on average four to five per cent higher in children of first cousins than equivalent non-consanguineous offspring.

“This is a complicated topic. Our findings over years of research have shown that the health risks associated with consanguineous marriage have been exaggerated, largely due to flawed research design, with a failure to allow for non-genetic factors that can adversely influence health outcomes. For example, many of the countries in which first or second cousin marriage is more common are afflicted with poverty which can have a devastating effect on early health and development.”

Prof Bittles said more research was urgently needed into the outcomes of consanguineous marriages because of the number of people involved and he hopes his book could be a catalyst for this work.

“The central aim in my work is the prevention of genetic disease through a better understanding and appreciation of how genes are transmitted within families and communities,” he said.

“In my book I discuss consanguinity and disorders of adulthood – the first review of its kind which is particularly relevant given the ageing of the global population. But more work in this area is needed.

“To date the principal disease focus has been on early childhood, with an emphasis on disorders such as congenital heart defects. As yet there has been very little work focused on possible health outcomes of common adult disease states, such as coronary heart disease and diabetes.”

As well as analysing scientific data, Prof Bittles provides detailed information on past and present religious and social attitudes to consanguineous marriages in his book. The related legal practices and prohibitions are also examined and the final three chapters deal in detail with practical issues including genetic testing, education and counselling, national and international legislation and the future of consanguineous marriage worldwide.

“My major intention with this book was to produce a reasoned and balanced overview of the topic which should both be readable to members of the general public but at the same time provide appropriately detailed information for scientists and clinicians,” he said.

Consanguinity in Context can be ordered online and e-versions will also be available after its launch on May 7.

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Comments (2 responses)

James Balano September 8, 2013

Census data from first century Roman Egypt strongly suggests that @ 25% of marriages in the Fayoum district were between siblings without noticeable depression in the birth rate or increased infant mortality.
Is there any scientific basis for the notion that close inbreeding over time tends to eliminate lethal genes from the gene pool and that the effect of consanguineous marriage has been exaggerated? As a corollary, is it possible that consanguineous marriage can actually improve the gene pool?

James Balano September 20, 2013

To support the deleterious theory of incest/inbreeding avoidance, human sociobiologists have repeatedly emphasized Edward Westermarck's hypothesis (1891) that children raised in close proximity will develop an aversion to sexual relationships with each other. Sociobiologists assume that this aversion originated as a naturally selected mechanism. Human sociobiologists site evidence from two case studies of human communities in support of Westermarck's hypothesis.
One group, the Israeli kibbutzim, separate children from their parents' household at birth and raise them in age-graded cohorts. In these cohorts boys and girls are raised without segregation, even sharing sleeping, bathing and toilet facilities; the proximity and intimacy of their upbringing is greater than what would usually be expected among siblings. Joseph Shepher (1983) studied these kibbutzim as a test of Westermark's hypothesis and reported that of the nearly 3,000 kibbutzim marriages he examined there was not one case of intra-cohort marriage.
However, several other researchers reported compelling research results which demonstrate that there are numerous social structural and ideological reasons why individuals of the same kibbutzim cohort might not marry (Talmon 1964; Spiro 1965). Mordecai Kaffman (1977), on the other hand, reported that by the late 1970s sex and marriage between cohort members had become common. John Hartung (1985), in re-analyzing Shepher's research, reported that not only did cohort members from Shepher's samples marry but did so at a disproportionately higher rate than would be expected for marriages involving non-cohort members. He also cited Shepher's research as one of the more egregious examples of bad science.

A second case study, often sited in support of Westermark's hypothesis, was published by Arthur Wolf (1995). Wolf studied a form of Chinese marriage known as minor marriage (or sim pua marriage). In this marriage custom a family adopts a young girl and raises her as a sister to their son. This adopted sister will eventually be the son's wife. Because these marriages had a higher divorce rate and produced fewer children than Chinese "major" marriage, Wolf and the human sociobiology community presented this research as primary evidence in support of Westermarck's hypothesis.
Wolf makes it clear, however, that the Chinese consider sim pua unions to be low-status marriages for the poor, and these marriages are often the object of public ridicule and scorn. Adopted daughter-in-laws are frequently mistreated and unhappy, and given the suggestion of incest in a sibling relationship, it is a wonder that such marriages worked at all. In other words, there is no need to invent a complicated Darwinian mechanism to understand why the Chinese minor marriages more often failed.
Another area of research that refutes Westermarck's hypothesis is from studies of nudist communities. Dennis Craig Smith and William Sparks (1986) found that nudist children experience more sexual play with siblings and have more incestuous relations with immediate family members than non-nudists even though their early associations are quite intimate.
It is annoying that researchers continuously trot out the Westermark effect in support of the sociobiological argument for the incest taboo when it stands on such shaky legs.

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