Many people are probably aware that in the past only half of each generation survived in Ireland to the age of 30. It is generally believed the other half emigrated. Many of them did, but a remarkably high proportion never got as far as emigration: they died early. At the time the State was founded, one in 10 babies died before the age of three (one in every eight in Dublin). By contrast, over 99 per cent of babies now survive.
Moreover, partly due to the ravages of TB in young adults, one in six died in Ireland before reaching 30. Allowing for those who died young after emigrating, it is clear that only four out of five survived to reach the age of 30, either here or elsewhere. Now, the post-natal death rate for young people is negligible, and some 97-98 per cent survive to age 30.
Of the survivors of the generation now reaching the age of retirement, as many as three out of seven emigrated. Thus, less than half of the males born in the early 1930s were alive in Ireland 30 years later, and barely half of the females.
Let me put it another way. Last year's census showed that almost 80 per cent of those born 26 years earlier were alive and in Ireland. Forty years ago, the equivalent figure for 26 year olds was about 57 per cent. Half of that difference is accounted for by the fall in the death rate of children and young people during that time, and half by reduced emigration.
Young people are still emigrating. Last year's census shows that one-fifth of males and one-sixth of females born 26 years earlier were outside Ireland when it was taken.
But what we are experiencing now is a different kind of emigration from any we experienced in the past. Many of those now outside the State are temporary emigrants.
Some are studying abroad with a view to returning when qualified, but more often they are acquiring experience they intend to use back in Ireland. And many have already returned. To take one example: the 1996 census figures suggest that, whereas one-sixth of the females born in 1959 had emigrated by the time they were 26 years of age, over a quarter of these were back in Ireland 10 years later. In addition to the more than 1,000 people who retire here each year, there is, of course, an average net inflow of 5,000-6,000 emigrants over 25 years old who have been returning to work here each year, bringing with them a similar number of children. It is this inflow of older emigrants and their children that has been more than balancing the continuing net outflow of younger people, thus halting the erosion of our population.
While many of the younger people who emigrate are leaving from their parents' homes rather than accommodation of their own, and thus do not release spare dwellings, the returning workers - many of them Dublin-bound - have to find somewhere to live, and this has been placing considerable pressure on our housing stock.
This inflow of older returning emigrants, most of them with families, has accounted for a significant part of the recent upward pressure on house prices, especially in Dublin but also in other expanding centres of employment, such as Galway.
On the other hand, in some areas the children of these returning emigrants are helping to fill school places which, particularly at primary level, would otherwise be falling vacant as a result of an over one-third reduction in the birth rate between 1980 and 1994.
However, at least in parts of south Dublin where there have already been major increases in residential occupancy in recent times, this further inflow of families with young children is creating pressure on already over-stretched school accommodation. From whence do these emigrants come? Less than half of those who went to the US in the late 1980s seem to have returned, but although there was a further temporary jump in emigration to that country in 1993 and 1994, before the present boom got under way, both in the early 1990s and again in 1995 the transatlantic flow was balanced, with the number of returning emigrants equalling those leaving for the US.
The flow to and from both Britain and the Continent was also well balanced during most of the first half of this decade. But in 1994 and 1995 there were annual net inflows of 2,500-3,000 from Britain and 1,500-2,000 from the Continent. Finally, emigration to parts of the world other than Europe and the US should not be under-estimated.
During this decade almost one-fifth of our emigrants went to overseas destinations other than the US - but, despite the distances involved, this overseas emigration has been no more permanent than that to countries nearer to hand.
The truth is that emigration today is totally different in character from that which we knew in the past. It seems clear that the majority of those leaving in recent years to work elsewhere did so with the intention of returning home. And a large proportion do in fact come back - many of them bring children born to them abroad, whom they wish to see educated here rather than in a country where they have worked for a period.
Another measure of the scale of the return of emigrants is provided by 1991 data which shows that in April of that year, excluding infants of less than a year, there were almost 22,000 Irish-born people living here who one year earlier had been resident elsewhere - 13,000 of them in Britain, almost 3,000 in the United States and nearly 2,000 in Australia or New Zealand.
OF course, even in the past, when economic conditions here were much less favourable than today, there were always people who returned from periods abroad. The fact that one in 10 Irish residents has spent a year or more outside the State understates the scale of this phenomenon, for clearly relatively few children have had this experience.
In 1991, one in seven adults had been away for over a year and one in six of those aged 45-54 - the age range of most of those who returned in the 1970's to jobs in Ireland.
And, as is pointed out in the ESRI's mid-term review of the Irish economy, in the case of women aged 45-75 who had third-level education, the proportion who have lived other than in Ireland for a year or more is as high as one-third.
Last year, Irish residents made 2.75 million visits outside the State - of which 750,000 were made to relatives abroad. Even allowing for the fact that many individuals make multiple visits each year, it is clear that a high proportion of the five-sixths of our people who have not lived for over one year abroad have been outside the State quite frequently for shorter periods.
A people of whom such a high proportion has had experience of other places, whether for shorter or longer periods, could never have been kept in the kind of spiritual and intellectual isolation that its spiritual leaders, and some political leaders such as Eamon de Valera, sought to impose up to the 1960s. The failure to appreciate the futility of such a policy has since been responsible for some, at least, of the difficulties we have experienced in coping with the increasingly rapid changes in our society.