Of those born in Ireland prior to 1940, almost one-sixth died young, mainly due to a high rate of infant mortality and the toll taken by TB among teenagers and young people in their 20s. Another one-third of the young population had to emigrate, with the result that in Ireland up to the 1960s no more than half of those born survived in their homeland beyond the age of 35. That is why today we have many fewer older people than other European countries, writes Garret FitzGerald.
All this began to change radically when Seán Lemass succeeded Eamon de Valera as taoiseach in 1959 and proceeded to reverse de Valera's - and his own - earlier inward-looking, protectionist policies, which had stunted Irish economic growth, especially in the 1950s. In this approach he was following a lead that had been given by taoiseach John A Costello three years earlier and by the young secretary of the Department of Finance, T K Whitaker, in his First Economic Programme of 1958.
By the late 1950s, the high death rate amongst the young was already in decline, and the reversal of the absurd policy of trying to make our part of this small island self-sufficient speedily led to the economy starting to grow at over 4 per cent a year.
Emigration soon began to respond to this situation, with the result that within little more than a decade we had moved to a situation in which emigration had been sharply reduced and we were starting to experiencing a net inflow of returning Irish emigrants. Already, by the end of 1963, the take-off of the Irish economy was well-enough established, and the drop in emigration sufficiently evident, for me to be able to forecast in my Irish Times column - accurately as turned out - that within the decade or so ahead our marriage rate would rise by 40 per cent.
Up to then we had remained a predominantly rural society: three out of every eight workers were still engaged in farming. And farmers married late; indeed many never married at all. But now that young people were remaining in much greater numbers in what was becoming an increasingly urbanised Ireland, there were bound to be far more marriages.
The proportion of those born in the State who remained, alive, in Ireland, at age 35, rose in the 1960s and 1970s from 50 per cent to 85 per cent - an increase of over two-thirds. The overwhelming majority of these young people married, mostly at an early age, right up until 1980. This more than out-weighed the decline in marital fertility that had begun in the mid-1960s, with the arrival of the contraceptive pill. So our birth rate rose by one-quarter during the 15 years between the mid-1960s and 1980.
What was most striking about the 1960s and 1970s was the young age at which couples married. As late as 1982 - only a quarter of a century ago - four out of every five women were married before the age of 28, and well over half before the age of 25. Less than one in 20 waited until after the age of 35 before marrying. Naturally this contributed to the relatively high birth rate: the number of births peaked in 1980, at 74,000.
Thereafter a huge change took place in our social mores. Between 1982 and 1995 the proportion of marriages under the age of 25 fell from 55 per cent to barely 30 per cent, and the birth rate dropped by one-third. To-day less than 12 per cent of women marry before reaching the age of 25.
A big factor in this process, particularly after the resolution of the financial and economic crisis precipitated by the disastrous policies of the Lynch/Haughey governments between 1971 and 1981, was the movement of married women into employment.
Basically, after about 1980 most women began to postpone marriage until their 30s - preferring to spend 10 to 15 years in employment before embarking on marriage and child-bearing.
Some, indeed, have chosen cohabitation rather than marriage, but for the most part what seems to have taken place has been the postponement of marriage rather than its abandonment. Indeed between 2002 and 2005 marriage began to come back into favour: the marriage rate has actually increased by about 10 per cent, because although the number of women of marriageable age has declined, the number of marriages has actually risen slightly.
What is most striking in all this is the very large increase in late marriages. By 2005 the marriage rate for women over 35 had trebled - and if this trend has since continued, it is likely that this year one out of every five marriages will have involved women aged 35 or over - with a corresponding increase in the number of births occurring to women over that age.
This is a sub-optimal situation, and public policy should, I believe, be directed towards easing the tensions that women experience in often having to choose between work and child-bearing, for example, by facilitating childcare for working mothers - the inadequate provision for which is clearly one of the causes of late marriages and late child-births.
The most desirable form such action could take would be the introduction of adequate maternity and paternity leave, which in some Scandinavian countries gives parents a total of up to four years in which to have children early on, and then to care for these children in early childhood.
Any society seriously concerned about the future of its younger generation - which means the future of society itself - ought to give a high priority to this issue. The fact that we in Ireland appear little preoccupied with this matter is, I feel, disturbing.
Now that we know just how great has been the shift towards later marriages, we need a serious debate upon this issue.
• Next week's article will deal with aspects of marriage breakdown.