At a time when, according to the Garda, serious crime rates are plummeting, crimes against old people - often for paltry sums of money, sometimes involving outrageous sexual assaults - are just one of a number of trends that caution us against complacency, and indeed raise disquieting questions about the changing nature of Irish society.

In the last few years there has been a sustained increase in the number of homicides, including numerous drug-related gangland killings, many, almost casual, deaths arising from late-night drunken assaults, along with increasing racist violence and a continuing incidence of serious sexual violence.

Recent improvements in crime rates are mainly restricted to property offences, and can be linked to the buoyancy of the economy, more rigorous law enforcement measures and, crucially, the adoption of harm reduction measures, such as methadone maintenance for drug-abusers who account for the bulk of such crime.

Disbelief about attacks like the one on the Logan brothers arises from our inability to understand the thinking processes and actions of someone who rides roughshod over some of the most sacred taboos and deeply ingrained inhibitions of civilised society. How does the unthinkable become do-able?

Respect for parents and the aged, and concern for their vulnerabilities, are the bedrock of civilised conduct in all societies. These crimes appear especially depraved because we expect respect for older people even from men hardened by the criminal culture of toughness and violence. Any self-respecting macho male, one might think, would find it shameful and beneath his dignity to stoop to violence against the elderly.

Scientific attempts to explain violence are inevitably hamstrung by the complexity of the area. But, if we are to get beyond the tautologies that tell us evil deeds are committed by evil people or deeply disturbed, perverted people, we must describe carefully the paths that lead people to violence and to fundamental breaches of the code of civilised conduct. This can never be easy because a thorough analysis must take account of the many interacting biological, psychological and socio-cultural factors that shape the individual.

It is also important to recognise that situations and events have their own compelling dynamics and that we must not seek explanations solely in terms of individual motives and personal histories.

All confrontational crimes, even relatively minor assaults and robberies, are unpredictably volatile and have a real potential for violence, especially if an assault is met with resistance. Offenders are often in a dangerously stressed and excitable state of mind, in which they think in highly constricted ways and can easily lose control.

It would be wrong to assume that all people who attack the elderly are by nature sadistic bullies or pathologically lacking in empathy for others. It would also be wrong to assume that they have always embarked on the crime with a prior, rationally calculated commitment to using violence or even any thought that they might do so. Denial and expedient thinking are part and parcel of the tools in trade of the criminal.

All humans have a capacity for defensive and offensive aggression, although there are significant differences between the sexes, and between individual males in the genetically-based inclination to violence. The disinhibiting effect of alcohol on the brain is often a major biological factor in the precipitation of violence. While such biological factors are crucial, central is the socialisation process by which we shackle our aggressive tendencies.

Occurring mainly in the family, but also in schools and the local community, socialisation is the process whereby we teach children values and rules of conduct, including co-operation, sympathy with others and the capacity for self-discipline. Inadequate socialisation can lead to impulsiveness, an inability to control aggression, and indifference to the feelings and interests of others.

Negative experiences within the family, especially brutal victimisation and exposure to adult models of violent domination, can teach children how to be violent and how to exploit violence for their own ends in the absence of any physically-based predisposition for violence.

While deficient socialisation helps explain how individuals can become callously brutal, the broader social context can also make a significant contribution to the increasing incidence of cruel attacks on the elderly.

The immense lifestyle changes and the growing confusion of value systems, both religious and secular, in modern Ireland have impacted powerfully on the content and quality of socialisation provided for our young people.

The attacks on the elderly are partly the product of changing social realities and socio-cultural norms. They are extreme manifestations of a more general shift in social structures and attitudes that has repositioned and in some ways devalued older people in Irish society.

Symptomatic of changed attitudes are the many young people who never seem to consider giving up their seat on a crowded bus to the arthritic old woman or man burdened down with shopping. A more serious example is the largely neglected problem of elder abuse by caretakers and adult children.

The demise of the traditional Irish extended family has led to the growing isolation of older people, and now more than a quarter of older people live alone. This means that fewer and fewer young Irish people are familiar with their elders or regularly interact with them in settings where the old have a meaningful and respected role within family and community.

The growing emphasis on material success and Ireland's current love affair with its brashly confident youth culture further marginalise older people and for some young people underline the irrelevance and nuisance value of non-economically productive older people, who obstinately hang on to their possessions.

A swift and successful pursuit of the perpetrators of the attack on the Logans, greater police and community vigilance, more support for the isolated elderly and effective alarm systems are obviously valuable countermeasures.

However, at the level of broader society, there is an urgent necessity to reverse the trend of marginalisation of our older citizens. If we are to educate our children to believe that we owe a special duty of care to the vulnerable elderly, we must find ways of fully integrating them into family and community life.

Dr Paul O'Mahony is the author of Prison Policy In Ireland: Criminal Justice Versus Social Justice, published last month