James G. Leyburn

“Lowlanders who left Scotland for Ireland between 1610 and 1690 were biologically compounded of many ancestral strains. While the Gaelic Highlanders of that time were (as they are probably still) overwhelmingly Celtic in ancestry, this was not true of the Lowlanders. Even if the theory of 'racial' inheritance of character were sound, the Lowlander had long since become a biological mixture, in which at least nine strains had met and mingled in different proportions. Three of the nine had been present in the Scotland of dim antiquity, before the Roman conquest: the aborigines of the Stone Ages, whoever they may have been; the Gaels, a Celtic people who overran the whole island of Britain from the continent around 500 B.C.; and the Britons, another Celtic folk of the same period, whose arrival pushed the Gaels northward into Scotland and westward into Wales. During the thousand years following the Roman occupation, four more elements were added to the Scottish mixture: the Roman itself—for, although Romans did not colonize the island, their soldiers can hardly have been celibate; the Teutonic Angles and Saxons, especially the former, who dominated the eastern Lowlands of Scotland for centuries; the Scots, a Celtic tribe which, by one of the ironies of history, invaded from Ireland the country that was eventually to bear their name (so that the Scotch-Irish were, in effect, returning to the home of some of their ancestors); and Norse adventurers and pirates, who raided and harassed the countryside and sometimes remained to settle. The two final and much smaller components of the mixture were Normans, who pushed north after they had dealt with England (many of them were actually invited by King David of Scotland to settle in his country), and Flemish traders, a small contingent who mostly remained in the towns of the eastern Lowlands. In addition to these, a tenth element, Englishmen—themselves quite as diverse in ancestry as the Scots, though with more of the Teutonic than the Celtic strains—constantly came across the Border to add to the mixture.”
― James G. Leyburn, Scotch-Irish: A Social History

“People who migrate are usually either dissatisfied at home or ambitious to improve their lot; but upper classes are already successful, and so have no reason to go to a wilderness to start afresh.

Plain as these facts are, people still look for distinguished ancestors. It seems not to be enough that one's family tree shows decent, ambitious, God-fearing people; they must be wellborn.”
― James G. Leyburn, Scotch-Irish: A Social History