I believe that the descent may well have been through a natural son, one born out of wedlock. I believe it very unlikely that brothers James and Humphrey and their nephew, James of Ramoran, had only daughters. Natural children were not uncommon in those days. James, 13th Galbraith Chief, had a natural son named Walter who later received "letters of legitimation" in 1558. Robert, 17th Chief, also had a natural son, Walter, whom he placed with a Helen Galbraith in Stirling. We only know of this natural son because he failed to pay Helen and in 1606 she brought suit against him for "twa zeirrs susteinment" of Walter, for which she received "three score sax punds money." So this Walter was born in 1604.
The histories and documents of the period make little or no mention of natural children. While natural children would certainly have been known to others, I think they were generally deliberately omitted from the historical record. Were it not for Helen's lawsuit, for example, we would be unlikely to know of 17th Chief Robert's natural son, Walter.
I have wondered if brother William Galbraith might have been a natural son of James Galbraith of Balgair. There are found very few references to him, while there are many to his brothers, James, Robert, and Humphrey.
I also wonder if the unnamed aunt, who married Thomas Lucy, if she were a Galbraith, might also have been a natural daughter, which could have been responsible for her being omitted in the historical record. There was also a genuine brother, Andrew, mentioned in Robert Galbraith's will, who had a son Humphrey, to whom Robert left 20 pounds "to put him to a trade." Neither Andrew nor his son, Humphrey, appears in historical accounts of the period. These Donegal Galbraiths were an elite family of members of parliament, landowners, army officers, and ministers and did not work at "a trade." Perhaps Andrew was the natural son of James Galbraith of Balgair and/or perhaps Andrew's son; Humphrey was a natural son. The family histories and accounts of the Galbraith brothers all indicate that James Galbraith of Magevelin had four daughters, all of whom, as it happened, married Hamiltons. But other less formal accounts state that there were two additional daughters, one of whom married a Sir Harry Echlin and the other a member of the Babington family. Were these two daughters natural daughters?
Others have claimed that a John and a Hugh were also brothers of James, Robert, Humphrey, and William. Perhaps they were natural sons as well. For that matter Elspet Galbraith, recorded in the 1665 Hearth Money Roll as living in Rateine, might have been the natural daughter of one of the Balgair Galbraiths, still living in the townland to which they had originally come in 1615.
James Galbraith, the paterfamilias of the 1718 Galbraiths, was born in 1666. From which one of the descendants of James Galbraith of Balgair might he have been descended? It might have been brothers James or Humphrey, both of whom had no sons according to the record. He might also have been descended from James of Ramoran, who was a wealthy man with no recorded sons. James of Ramoran was younger (b.1620-1630); he might barely have been the grandfather of 1718 James (b. 1666), or possibly he was his father. If he were his father, it would have been contrary to the limited evidence indicating 1718 James's father was a John Galbraith, but, as we have seen, the naming pattern was not always followed.
If a man had a legitimate son, he might not bequeath much to that son's illegitimate brother. But if a man had no legitimate son and a natural son he cared for, he might leave a lot to that natural son, particularly if all his daughters had married well. The descent then might have been from James Galbraith of Magevelin. Perhaps he had a natural son, whom he named John; and this John was the father of 1718 James Galbraith (named after his paternal grandfather), who in turn named his oldest son John. The descent might also have come from James of Ramoran, who was a wealthier man than his uncles. Probably the descent did not come from Humphrey, for there are no Humphreys among the descendants of 1718 James.
I don't think there was much stigma attached to natural children. I suppose the father arranged for the child to be cared for elsewhere. Their wives certainly would not want evidence of their husbands' behavior, or misbehavior, in their homes and probably just muttered "Men!" to themselves in disgust. If, then, James of Magevelin had a natural son whom he named John and to whom he bequeathed a substantial amount, he might perhaps have parked the boy in Newton Cunningham, where Sir John Cunningham, an uncle of Jean Cunningham Galbraith, brother Robert's wife, had received a sizable land grant.
If the descent were through James of Ramoran, he too might have parked the boy in Newton Cunningham, where his mother's uncle had established a village on his land grant. That could account for the reference to Newton Cunningham found in the history of Rebecca Galbraith, a daughter of 1718 James Galbraith (see below).
Perhaps such a natural son might have married well and/or his son, 1718 James Galbraith, the immigrant, might have done the same. That might have accounted for his apparent wealth when he arrived in Pennsylvania. Or, more speculatively, perhaps the Cunninghams of Newton Cunningham gave him a helping hand. Sir John Cunningham probably had no sons, for in the 1654 Civil Survey of Ireland the property at Newton Cunningham was owned by Sir John's co-heiresses, probably his daughters. If his property were still in their names and not in the name of any husbands, possibly they were unmarried and had no immediate heirs. If a natural Galbraith son became established at Newton Cunningham, and if he were a good man, might not those two co-heiresses have also left him some money? He was a relative; Cunninghams and Galbraiths had always been close in Scotland and in Ulster; and Sir John had made a success out of the property he acquired in his land grant and must have become fairly wealthy. So perhaps those two co-heiresses helped him. That is merely conjecture. There is no substantiation of it in the historical record.
So there is a theory. It is a reasonably plausible hypothesis, which may be proved or disproved when, hopefully, more of the actual historical record comes to light. If this theory is correct, we have charted the 1718 Galbraith immigrants in Pennsylvania from their origin in Balgair in Scotland through their stay of 100 years or so in Ulster to their arrival in America. It is possible another scenario could explain these facts, but I have been unable to come up with one.
In the meantime all we 60 CGA members who are descended from the 1718 Galbraiths might consider ourselves the natural descendants of James Galbraith of Balgair. (But I don't suppose we need letters of legitimation.)