The ABO and Rh blood groups of the Aran Islanders

Summary and Conclusions

We have shown that the ABO and simple Rh blood group frequencies of the Aran islanders are different from those of the adjacent mainland of the west of Ireland. Such differences might very reasonably have been expected to be extrapolations of the east-west gradients already known to exist in Ireland. In fact they are the opposite, taking the form of a similarity to the frequencies found in the east of Ireland or the north of England where, in both places, the existing frequencies are probably the result of a mixing of Gaelic and English stock. There are, doubtless, other places in Europe (or in the world) where similar frequencies occur, but we have made the foregoing comparisons because of historical and anthropometric evidence suggesting that the Aran population could be a mixture of Irish people with English. This hypothetical mixture would have occurred in the seventeenth century just before the time of the general introduction of the potato to Ireland, which was an economic factor that could have promoted the establishment and expansion of the mixed stock on the islands.

When a hypothesis based on independent historical and anthropometric evidence turns out to be in positive accord with blood group findings, it is then reasonable to interpret the blood group findings as giving the hypothesis valid support, unless there is a better alternative explanation.