I have a fit o' Irish now and then. When I'm roamin' comes the foamin'.... Wait. That didn't get off to a good start. :-)

This is a fascinating article about the discovery of some bones under a pub and how they've led a re-evaluation of the Irish and Celtic people. It's long been thought that the Celts moved from continental Europe, to the islands, and became the Irish. But now it seems that may not be so. They may have actually moved the other way, from the western fringes of Europe toward its heart. Well worth a read.
Drop a rock in water and it spreads in a circle. Life is like that too with one exception, life takes the path of least resistance. If life started in mesopotamia it more than likely would have spread over all available land mass before venturing across the sea to Ireland. As for the theory that Ireland may have been founded by fishermen or traders blown off course, that has one fault. There would have been no women in these boats. Which means they would have had to retrace their steps. Still it is possible if you consider the choicest lands were on rivers and on the sea where food was easiest available. Early sea farers never left sight of land. Is it possible to see both shores, England and Europe if you are half way between? In a small craft? 
Well anything is possible considering that there was life almost everywhere before the explorers in 1492.

An even wilder theory would be that there was more than one Ark and more than one noah and life spread that way. That the whole earth was not covered by water but only low lying areas and life could be supported where the arks settled. Well this would explain how animals got to these remote places.