Until the middle of the nineteenth century, Irish tenant farm holdings underwent a cultural tradition of sub-division, whereby the tenant's land was divided equally between all the sons, both legitimate and illegitimate, on his death. The result was that by the 1840s, many farms had become so small that the only food source that could be grown in sufficient quantity to feed a family was potatoes. This was to have disastrous effects when, in the period 1847-49 potato blight struck, making much of the potatoes grown inedible. This period came to be known as the Great Famine and cost the lives of well over half a million people.
Subsequently, a change in the law required that the tenancy go to only one legitimate son. With the wholecale deaths and largescale emigration of the period, farm sizes had begun to increase, as surviving holdings were merged with neighbouring vacated ones. The prohibition of sub-division ensured that in normal circumstances they would not decrease in size any further.
A secondary effect of the prohibition of sub-division was that other sons, who previously inherited part of the family farm tenancy, instead was forced to seek employment elsewhere. Many emigrated. Many chose a route of entering a religious life, as a Roman Catholic Priest, Nun or Religious Brother, such options becoming available due to a re-organisation of Roman Catholicism in Ireland under Cardinal Cullen in the 1850s and beyond. This influx of young men into the religious life, thanks to the disappearance of sub-division, in part explains the massive growth in clerical numbers in Ireland in the period.
Irish land holdings underwent further massive change in the period 1880s-1930s when a series of Land Acts broke up the previous large estates from which farmers rented property, the farmers through British Government grants and loans being empowered to buy their farms instead of renting them.
