The biology of divorce

In the current climate and controversy relating to the topic of divorce it is well to look laterally at the problem and ask whether biology has anything to offer in relation to this complex issue - particularly some aspects of human biology which have all but been neglected or misunderstood.

In the first place, the biology of attraction and interaction between the sexes resulting in the choice of a mate is very much under the control of biological factors which work surreptitiously and subliminally to control our actions.

The role of pheromones in this context has now become well known. Pheromones are chemicals secreted by glands as markers of a physiological state: in particular, sex pheromones are crucial in attracting a mate.

A second curious phenomenon relates to avoidance of mating among those who are genetically too close to one another. Again this tendency is very much related to basic biological make-up. The HLA system is a complex system of protein markers essential for cell-cell recognition. Each individual is unique from the point of view of HLA constitution, and this is what makes transplant procedures between different individuals a hazardous affair.

It has been known for a long time that partners who differ strongly in their HLA make-up are more likely to produce more robust offspring; and vice-versa, in those couples whose HLA are closely similar, as may happen in marriages where the partners are related, there is a greater chance of weaknesses appearing in the child.

What was not clear is how choice of partner can depend on the genetic (HLA) make-up of the individual. The now well-established pheromone attraction between two individuals has been shown to be related to their HLA make-up as measured, of all things, by body odour. Females were shown to be partial to body odour of some males and repulsed by others. This, it is claimed is an important basis for partner selection.

One complication that has intruded into this natural way of selecting a partner has been the contraceptive pill. Recent work has shown that one action of the pill is to suppress these pheromonal influences, masking the natural ability of choosing the right mate. In other words, those on the pill may not be able to make a correct biological choice of partner. The result of this is that after stopping taking the pill, any discrepancy or mismatch will come to the fore and result in partner dissatisfaction. This, it has been claimed, could be another reason why a couple might become distant from each other.

Another interesting aspect relates to what has been called the "divorce gene". This gene is responsible for producing a variant of 'vasopressin', a hormone produced by the brain (hypothalamus) and released slowly into the circulation. For a long time it was known that this hormone was essential for the control and retention of water in the body, preventing excess water loss. It has also a role in controlling the blood pressure by producing constriction of the arteries.

In addition to these basic physiological functions, vasopressin was known to have other interesting effects on behaviour, including pair-bonding in voles. What comes as a great surprise is the finding that it may well have a similar crucial role in holding human couples together.

A recent study from the Karolinska Institute in Stockholm, reported in the prestigious journal Proceedings of the National Academy of Sciences, shows that there was a close correlation between the action of vasopressin and scores obtained from the 'Partner Bonding Scale' which assesses the degree of attachment among couples. A variant gene was found to yield lower levels of vasopressin.

A single dose of this gene resulted in low scores on the scale and men with this condition were less likely to be married, and their wives less likely to be satisfied with the marriage. A double dose of the gene results in an increased likelihood of having a marital crisis.

Hass Walum, who leads this research group, says that "this is the first time that a specific gene variant has been associated with how men bond to their partners", and suggests that some of the most fundamental social interaction could be dependent on the action of little-understood genes.

On top of this ground-swell of biological activity, there is a whole superstructure of societal, moral, legal, psychological and religious factors which account for breakdown in marriages. The role of biological compatibility has perhaps not been given sufficient emphasis in discussions of this topic.