THE EDITOR, Sir:

On MARCH 19, 2007, you printed an article on recent decisions regarding the legal definition of incest in Jamaica. Titled 'Kinder laws for kissing cousins', the article reported that a joint select committee of Parliament had taken the decision to exclude first cousin sexual relationships from the definition of prohibited incestuous relationships. Clearly, and perhaps appropriately, the legislative attention directed to incest in Jamaica seems focused on the often but not always related issue of carnal abuse. Indeed, discussions of the carnal abuse problem in Jamaica have been much in the news of late, including a debate over raising the age of consent.

What was missing from that article was the drawing of a clear distinction between carnal abuse, other forms of sexual predation (such as rape), and the issue of incest. Carnal abuse refers to cases when an adult engages in sexual activities with an individual under the age of consent (16 in Jamaica), regardless of familial relationship; rape refers to the criminal act of forcing sex upon another individual, regardless of age; and incest is defined as sex between genetically-related individuals.

My purpose here is not to address the legal ramifications of incest, but rather, to clarify the biological consequences of sex between genetic relatives. To be sure, essentially all human societies, including so-called primitive societies, have incest taboos. The reasons for this are obvious: the offspring of related parents tend to be less healthy and are more likely to display reduced survivorship or other unfavourable characteristics. Put more formally, deleterious recessive traits are much more likely to surface under conditions of inbreeding, and the probability of inbreeding depression is directly proportional to the degree of genetic relatedness between the parents. This is basic genetics.

Historical examples of the pitfalls of inbreeding are plentiful, and include the Pharaohs of ancient Egypt, as well as numerous other illustrations provided by royal families. And more recent, scientific treatments of inbreeding have been equally dramatic. For example, one study compared mortality rates between the children of unrelated parents with the children of first cousin parents in a variety of different human populations. The results were definitive: mortality rates within populations were significantly higher among first cousin offspring than among the offspring of unrelated parents.

Other documented consequences of inbreeding include decreased fertility and sperm viability; increased incidence of genetic disorders (for example, Down's Syndrome); decreased facial symmetry; decreased growth rate (resulting in small adult body size), and reduced immune system function, among others. The public health implications of inbreeding are so obvious they should require no further explanation or demand any additional elaboration.

I am, etc.,

Dr. B.S. WILSON

Lecturer, Department of Life Sciences

UWI, Mona

Via Go-Jamaica