Genealogy is buncombe.

Certainly, our family trees are interesting — at least to us (in this, they resemble dreams, fascinating to the dreamer, but please, save us from having to hear about yours).

But, beyond a few generations, already known to you, the information involved is either or both too complex to be meaningful, or too corrupt. Yes, perhaps you can trace your line back to Charlemagne, but such a lineage is close to meaningless.

Take the complexity first. Genetically speaking, you have two parents, four grandparents, eight great-grandparents, sixteen great-great-grandparents. Each generation doubles the number of genetic strands in your makeup. Generationally, it goes 1 (you) -2 (parents) -4 (grandparents) -8 (etc.) -16 -32 -64 -128 -264 -528 -1056. Each generation doubling its number of ancestors. So, trying to follow just a single one — one that perhaps takes you back to Charlemagne — ignores all the others, whose influence is quantitatively the same.

Not to forget that not only do you have, say, 128 great-great-great-great-great-grandparents, but each and every one of them also had 128 great-great-great-great-great-grandparents. That is more than 16,000 people dumping DNA into your genome. How complete do you want that family tree when you sign on to Ancestry.com? How complete is possible?

At best, you can have only a very partial sense of your family background. And that is only one side of the problem. The other side is human nature.

We ran into this when my wife’s brother signed up for one of those y-DNA tests. Such a test follows the haplogroup of paternal lineage up through the generations, seemingly all the way back to its African origins. With random mutations along the way to give a sort of timeclock to the changes, a sense of where a certain male lineage was at a certain epoch is roughly possible. But that is only a line through father and father’s father and father’s father’s father, etc.

When we got back the result of my brother-in-law’s test results, we discovered that his (and by extension, my wife’s) paternal lineage came from County Cork in Ireland. (Before that, through Sardinia, the Middle East and back to Africa). The test also gave us the names of other people who had taken the test and found matches between them and brother-in-law. His name is Steele, and there are several Steeles named. But most of them are Driscoll, not Steele. My wife was puzzled. Most of those Driscolls still live in Ireland.

A little cogitation and the lightbulb goes on. Somewhere up the line, a woman had a child out of wedlock. Either she was married to a Steele and had committed adultery, or she was born a Steele and was a single mother, or had a baby out of wedlock and later married a Steele and her son was adopted. Somewhere back in history, the Steele patrimony was hijacked. A son bore the Steele name, but the y-chromosome of a Driscoll.

Did that young Steele boy know his real father was a Driscoll? Did his mother ever tell her husband who the father of her son was? We don’t know. Any version is just a story we make up. But the logic of the genes is clear: At some point the surname Steele was carried by a man not born to a Steele.

One has to imagine that this sort of thing happens all the time. Human nature being what it is, fatherhood is always a matter of convention and convenience. The actual line of DNA is uncertain.

Modern tests can give us some minute part of the information about where we came from, but whatever pride we might wish to feel about being related to royalty or fame is diluted to the point of meaninglessness by the admixture of everyone else who has gotten into the act. And the line we might trace out on a family tree only follows the surnames and marriage registers — the reality may be genetically hidden from us by some usurper as the randiness of human sexuality is taken into account. So, perhaps Charlemagne isn’t really your great-great-great etc., perhaps it was his groom, perhaps it was hundreds of years later that someone cheated and split surname from genome leaving you barking up the wrong family tree.

History is such an uncertain thing. My entire family, as far as we can trace it back, is Norwegian (with one Swede thrown in for good measure). Perhaps I am related to Erik the Red (or to Harald Bluetooth, or Ivar the Boneless — I love these old names). But any pride I might want to feel about a presumed Viking ancestry must balanced against the likelihood that somewhere unknown to me, there is an interloper in the family tree. Perhaps there is a Sicilian (Vikings conquered Sicily first in 860 and then again in 1038, first under Bjorn Ironside and then under Harald Hard-ass). So, who knows?

But more directly, every Norwegian I know in my family, going back as far as our records go, was as tame and toothless as any Norwegian bachelor farmer. My recent ancestors are the single most boring group of people ever assembled in a room to drink coffee and mutter quietly about drivel. Viking ancestry? No trace remains.

The whole point about genetics is that it is a crap shoot. You never know what you’re going to get. Bits of DNA might make it through the centuries and might give you the hazel eyes you bear, but most of the DNA of those thousands of copulations that ended in your ultimate birth have been filtered out, remixed and gummed up.

I can see the interest in plotting that family tree back three or four generations. Beyond that, it seems meaningless. I knew my great-grand uncle on my father’s side, and I knew my grandmother’s mother-in-law. They lived just long enough to be a sliver of my memory. Beyond that it is only a few names in a family Bible. Beyond that, all swallowed up in the forgetfulness of the grave.