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A study published in the American Journal of Human Genetics in 2005 entitled A Y Chromosome Signature of Hegemony in Gaelic Ireland describes how researchers sampled DNA from about 800 men from across Ireland and seem to have found genetic evidence in Northwestern Ireland which supports the idea that the historical ruling family of Ireland from the 7th through the 11th centurys (the O'Neills) may indeed be descendants of the 'mythological' Niall of the nine hostages as their name suggests (literally 'descendants of Niall'). For the biologically minded, you can download the article in PDF here (link dead 2013).

Historians have long suspected that the Irish myths may contain accounts of real historical events distilled through time and retelling, and that the long lists of relations in the myths may turn out to be genealogically accurate to some degree. This study seems to suggest that thinking is correct.

A Y Chromosome Signature of Hegemony in Gaelic Ireland
Am. J Hum. Genet., 78: 334–338, 2006
Laoise T. Moore,1,Brian McEvoy,1,Eleanor Cape,1 Katharine Simms,2 and Daniel G. Bradley1
1Smurfit Institute of Genetics and 2School of Histories and Humanities, Trinity College, Dublin
Received September 29, 2005; accepted for publication November 18, 2005; electronically published December 8, 2005.

Now we need DNA evidence to support the existence of the Tuatha de Danann and Firbolg...
There is a science fiction series by Julian May that speculates along these lines, and adds psychic powers and time travel on top of it.
The Saga of Pliocene Exile (The Many Colored Land, The Golden Torc, The Nonborn King, and The Adversary)
The book is populated by "Tanu" and "Firvulag," whose names are slightly modified versions of the Gaelic gods: e.g., Nodonn for Nuada, Lugonn for Lugh, etc.
Check it out sometime.

The full paper in the Journal Nature is of course not available for free, though you can buy the PDF for a reasonable charge. The abstract says this much:

We suggest significant pre-Roman but post-Mesolithic movement into southeastern England from continental Europe, and show that in non-Saxon parts of the United Kingdom, there exist genetically differentiated subgroups rather than a general ‘Celtic’ population.

The BBC article spells it out for the layman that... "genetically there is not a unique Celtic group of people in the UK. According to the data, those of Celtic ancestry in Scotland and Cornwall are more similar to the English than they are to other Celtic groups. The study also describes distinct genetic differences across the UK, which reflect regional identities. And it shows that the invading Anglo Saxons did not wipe out the Britons of 1,500 years ago, but mixed with them."

An article in Popular Archaeology discusses the findings of scientists from Trinity College Dublin and Queen's University Belfast who sequenced the DNA of the remains of some ancient Irish people. Their research supports the argument that there were indeed some waves of migration over time and that people who lived in Ireland before and after these immigrations looked very different genetically. While not mentioned, the implication is that the Irish mythological stories of invasions of various peoples throughout their history might have some basis in fact.

These ancient Irish genomes each show unequivocal evidence for massive migration. The early farmer has a majority ancestry originating ultimately in the Middle East, where agriculture was invented. The Bronze Age genomes are different again with about a third of their ancestry coming from ancient sources in the Pontic Steppe.

This article has been making the rounds lately. It discusses the genetic sequencing of some ancient individuals found in County Antrim. The DNA suggests that these very ancient peoples (4000 years ago) already carried the genetic signatures of modern Irish and the markers of mutations that are primarily thought of as Celtic, but long before the culture we call Celtic existed. Earlier burials (5200 years ago) contained individuals with genes which suggest affinity with Mediterranean peoples. These findings suggest that the ancient Invasion myths might have a basis in fact. It also suggests that what we recognize as Celtic might need to be redefined.

http://www.amazon.com/The-Origins-Irish ... 0500051755

"This is the first major attempt to deal with the core issues of how the Irish came into being. J. P. Mallory emphasizes that the Irish did not have a single origin, but are a product of multiple influences that can only be tracked by employing the disciplines of archaeology, genetics, geology, linguistics, and mythology."

I brought this book with me to the last meeting, Its no joke but surprisingly refreshing to read despite its academic credentials.

Anyone who wants a real in-depth study of the subject should ask to borrow it and read it cover to cover.

On a similar note, I've been toying with the idea of getting my DNA tested to see exactly where it will lead to. This also relates to a question Comyn brought up last meeting about the Fir Bolg....

They were an actual group of clans. They are believed by some to have more properly be the "Fir Belg" - the men on lightning - Belgic celts who may have settled parts of Ireland from the continent.

Mythologically/ folklorically speaking, the Fir Bolg were reputed to hold the holly sacred in distinction to mistletoe, they typical Druidic plant of choice.

One of the earlier / synonymous names of the McNamara clan was "Clan Cuilean" - the clan of the Holly.

Recent genetic research of members of the Dal Cais has found that the O'Brians and the McNamara share surprisingly less DNA than expected.

There is also this snippet from an antiquarian book on the MacNamara's:

Six generations on from Cormac Cas we have Cas. Having twelve sons of which the second was named Caisin. It is from Caisin that Clan McNamara takes it’s earliest name ‘Ui Caisin’ the children of Caisin. The territory ruled over by the Clan came to be known as Ui Caisin. Which comprised of a larger part modern day County Clare. The territory it’s self was formally known as Magh Adhair meaning the plain of Adhair. This was the name given to it by it’s pre Celtic inhabitants the Adhar, the Firbolg, who possessed the land in the first century.

So... It a conjecture on my part, but given all the above, and the fact that the Dal Cais supposedly moved into the area of Clare and took it over - Clare having changed hands between Connaught and Munster a couple of times, I wonder if the McNamara,s were older residents of the area that got absorbed by treaty. There are numerous stories of the Macs interceding on behalf of O'Brian dynastic struggles. If they weren't as closely related to the rest of the septs, it might have made them ideal as enforcers to beat on other clan members, and hence their position as hereditary marshals of the clan who had the right to inaugurate the OBrian as kings of the Dal Cais.

Also, of curiosity is Ptolemy's map of Ireland. The area of Clare lists a tribal name of "Gangani" or "Concani" Con means hound in Irish, Cani being Latin for dog it might be a stretch or coincidence, as I'm no linguist here but, of note, the only sept within the Dal Cais that I am aware of that has a canine related name is McNamara - which is a simplification of the original Mac Con na Mara - "Son of the Hound of the Sea"

As I said, it's conjecture on my part and there may be holes in the theory for lack of dates of certain events and misinterpretation, but I wonder if my DNA might lend a bit more fuel for the fire or douse it.

A new DNA study (discussed at lenth, with graphs, in this Daily Mail article) suggests that the Irish are far more genetically diverse than previously thought. Its been shown that most Irish have some Viking and Norman ancestry and those with more Celtic blood are found only in the west.