What is agnatic ancestry?

While reviewing Y-haplogroup information it is always important to keep in mind the profound difference between ordinary ancestry and agnatic ancestry. You have two grandfathers, four different great-grandfathers, eight 2-g grandfathers and so on. You have over a thousand 9-g grandfathers, over a million 19-g grandfathers, a billion 29-g grandfathers, and over a trillion 39-g grandfathers!

Ooops! That's impossible; the number of humans who've ever lived is less than a trillion. You have a trillion 39-g grandfather slots in your pedigree, but many of these slots will be filled by the same people. Charlemagne might appear a billion times in your pedigree!

And yet, among the thousand 9-g grandfathers, only one is your agnatic 9-g grandfather, your father's father's father's father's father's father's father's father's father's father's father. Among the trillion 39-g grandfathers, only one is your agnatic 9-g grandfather. Among the googols of 340-g grandfather slots, only one is the agnatic slot, the ancestor from whom your father inherited his Y-chromosome.

Indfhine and other Gaelic inheritance rules

In order to determine eligibility and settle claims (e.g. blood money for murdered kinfolk or ascent to a lordship) the earliest Irish and Scots people with written records show that they memorized agnatic genealogies, and we can infer that they're bards and Druids memorized these lineages long before there were written records! There seem to be traces of similar systems in ancient Hindu culture. The agnatic lineage is important in some cultures. And, while male invaders were often happy to mate with indigenous women, the genetic evidence shows that indigenous males sometimes had limited procreative success after an invasion.

Ancient Agnatic Lineages

Here's a (very ancient!) genealogical lineage you may be familiar with.

We ignore mother connections in the genealogies on this page, so twenty generations get condensed into a very short list. Adam had multiple sons, but the agnatic lines of all but Seth eventually went extinct. Similarly, all surviving human males have the Y-chromosome of Enos, and of Cainan, and indeed of all the males in the list until we get to Noah. Eber had sons other than Joktam and Peleg, by the way, but as far as can be found in Biblical genealogies, the agnatic lines of the other sons soon went extinct.

If we accept Biblical myth, then Adam is the agnatic ancestor of ALL living humans, as is Seth, Enos, etc. all the way to Noah. No other Y-chromosomes have survived. We're all descended from Noah's uncle Eliakim also, of course -- he was the father-in-law of Noah's sons, but Eliakim's agnatic went extinct in the Flood.

Noah had three sons each with living agnates. Men that have three or more sons with agnates living today are of special interest; we will label them NOAH, in acknowledgemnt of the first such (legendary) man. For each NOAH, all but one of the sons with living agnates apppears to his right in red (as Japheth and Ham do), while the son whose line we follow (Shem) appears below the NOAH. Noah's son Shem also fits the requirement for "NOAH". We will also speak of "EBER"s, who have two sons with living agnates, again named after a famous Biblical progenitor.

The Y-chromosome of King James I (and VI)

But we're not interested in the legendary ancestry of the legendary Prophets of Genesis. Instead we will focus on a particular Stuart family. And yet we will see that, like the line to the Prophet Eber, there are many ancestors along the way whose Y-chromosome survives in only a single son.

Stewart is a common surname in the British Isles and America. There are various different Stewart families, but many are descended from the ancient Lord High Stewards of Scotland -- it is that line we will consider.

We will root the tree at James Stuart (King James I of England). He has many living agnates (although many developed surnames like FitzRoy). The lineage has a clear character, albeit one which might be viewed in "racist" terms: We see the a single line of males "walking point", almost acting as "the tip of a spear."

By the way, 30 years is a good estimate, at least in historic times, of the generation gap between father and son. (24 years is a good estimate for mother-to-daughter gaps.) Here is the lineage of interest.

Quoted from Nichol (Gaelic and Gaelicised Ireland during the Middle Ages)

One of the most important phenomena in a clan-based society is that of expansion from the top downwards. The seventeenth-century Irish scholar and genealogist Dualtagh Mac Firbisigh remarked that 'as the sons and families of the rulers multiplied, so their subjects and followers were squeezed out and withered away; and this penomenon, the expansion of the ruling or dominant stocks at the expense of the remainder, is a normal feature in societies of this type. It has been observed of the modern Basotho of South Africa that 'there is a constant displacement of commoners by royals [i.e. members of the royal clan] and of collateral royals by the direct descendants of the ruling prince;, and this could have been said without adaptation , of any important Gaelic or Gaelicized lordship of late medieval Ireland.

In Fermanagh, for example the kingship of the Maguires began only with the accession of Donn Mór in 1282 and the ramification of the family - with the exception of one or two small and territorially unimportant septs - began with the sons of the same man. the spread of his descendants can be seen by the genealogical tract called Geinelaighe Fhearmanach; by 1607 they must have been in the possesion of at least three-quarters of the total soil of Fermanagh, having displaced or reduced the clans which had previously held it. The rate which an Irish clan could itself must not be underestimated. Tulrlough an fhíona O'Donnell, lord of Tirconnell (d. 1423) had eighteen sons (by ten different women) and fifty-nine grandsons in the male line. Mulmora O'Reilly, the lord of East Brefny, who died in 1566, had at least fifty-eight O'Reilly grandsons. Philip Maguire, lord of Fermanagh (d. 1395) had twenty sons by eight mothers, and we know of at least fifty grandsons. Oliver Burke of Tirawley (two of whose became Lower Mac William although he himself had never held that position) left at least thirty-eight grandsons in the male line.

Irish law drew no distinction in matters of inheritance between the legitimate and the illegitimate and permitted the affiliation of children by their mother's declaration (see Chapter 4), and the general sexual permissiveness of medieval Irish society must have allowed a rate of multiplication approaching that which is permitted by the polygyny practised in, for instance, the clan societies of southern Africa already cited.

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