I had my Y-DNA tested recently. This is different than the DNA tests you see on all the Ancestry TV ads. (For a detailed explanation of the difference, click here.) This could get technical very fast, but I’ll try to keep it simple. Don’t worry, there won’t be a quiz at the end!
Y‑DNA is passed down from father to son with each generation and remains unchanged except for infrequent minor mutations. These mutations occur at a somewhat predictable rate, which makes it possible to estimate how many generations have passed since any two men descended from a common male ancestor, going back thousands, or even hundreds of thousands, of years. Since surnames are commonly passed down from father to son, Y‑DNA can be used to determine whether two men with the same or similar surnames have a common male ancestor, even if that ancestor lived before the timeframe of most genealogical records (400 years or so).
For example, I know from my research that today’s Casbon surname originated in southern Cambridgeshire, England. I have also observed that the modern surnames of Casbolt, Casebolt, and Casburn seem to have originated in the same general area. As a matter of fact, these spellings were sometimes used for my ancestors before “settling down” to today’s spelling.
I’ve always wondered whether present-day people with these surnames are related. Do they descend from one person back at a time when surnames first came into common use (after the Norman Conquest in 1066)? Genealogical records do not extend back far enough in time to establish such a connection. Nor do autosomal DNA tests such as those you can order from Ancestry. But Y‑DNA can make that connection, and can even predict when the common ancestor might have lived. Hold that thought.
Here is my Y-DNA story
I tested with a company called FamilyTreeDNA. FamilyTreeDNA is widely recognized as the global leader in Y‑DNA testing, and they have the largest database of test results. The number of tests performed have exploded in recent years. The results have been used build a huge family tree of male ancestors. As more people test, the tree continues to expand and more branches, each representing a common ancestor, are identified.
As of December 2021, the FamilyTreeDNA Y-DNA tree had more than 50,000 branches. Each branch has a name, known as a haplogroup, identified by a series of letters and numbers. These branches are defined by specific mutations in the Y‑DNA. By comparing modern DNA samples to those of ancient skeletons, a timeline of when different haplogroups branched off from the tree has been built. This timeline goes all the way back to a hypothetical single male ancestor, commonly referred to as “Y‑chromosomal Adam,” who lived some 200,000 to 300,000 years ago.
Now back to my DNA Results. Preliminary results showed that I belonged to the major haplogroup R1b. This haplogroup is believed to have arisen in western Asia some 22,000 years ago. R1b has more than 25,000 branches (so far) and is the most common haplogroup for men of Western European ancestry. About 60 percent of men with English ancestry belong to the R1b haplogroup.
Further testing showed that I belong to a tiny sub-branch of haplogroup R1b labeled as R‑BY56807. The label is not important. What is important is that my closest matches are three men, all with the surname Larkin.
Why would I share DNA with someone named Larkin? I have no known ancestors with that name. Here is the likely explanation: although they are close matches, we do not share the exact same haplogroup. Based on the mutations we do not have in common, FamilyTreeDNA estimates that the most recent common ancestor of our two lines was born around 1150 CE (current era). This was about the time when surnames were just coming into use in England. This man had sons who eventually became known by the surnames Larkin and Casbon (or Casbolt or Casburn perhaps). Another possibility is that a non-paternal event, commonly referred to as an NPE, occurred. This means that a man had one or more male children who were raised with a different surname than his own.
Who was this mystery ancestor of the Casbon and Larkin lines? We will never know, because the records don’t go back that far.
Why are there no matches to someone named Casbon, Casbolt, Casburn, etc.? The answer is simply that no one with one of these surnames, besides myself, has tested with the complete Y‑DNA panel, known as Big‑Y 700, at FamilyTreeDNA. I have matches with two men, named Casbolt and Casebolt, who have taken less extensive Y‑DNA tests. These matches support my theory about a common origin for our surnames, but they are insufficient to say for certain that we have a common ancestor. What I really need is for more men with those surnames to get tested.
Where do I go from here?
Ideally, I would like to start a Y-DNA Group Project at FamilyTreeDNA for men with Casb___ surnames. Such a project would have a shared web page and links to DNA test results. I have tried to contact the Casbolt and Casebolt men who are close matches with me to see if they would be willing to upgrade their DNA tests to Big‑Y 700, but I have not received any replies. I am also looking for men with these surnames who have posted family trees on genealogy websites, to see if they might be interested in testing. Unfortunately, Y‑DNA testing is more expensive than the more common autosomal DNA tests, so this is another limiting factor. I have to admit that trying to trace the Casbon surname to its earliest origins is little more than an academic exercise. It’s an interesting pursuit, but not a pressing need, so such a project will only go forward if I can find and recruit men who share my interest.
That’s it for this post. I may delve more deeply into the subject of Y‑DNA, such as what it reveals about the migrations of our human ancestors, in a future post.
More about DNA testing
Most people know that DNA is contained in chromosomes within the nuclei of our bodies’ cells. Every cell has 23 paired chromosomes, with one chromosome in each pair coming from each of our biological parents. Twenty-two of these pairs are known as autosomes. The 23d pair holds the sex chromosomes: XX in females and XY in males. A female inherits an X chromosome from both parents, while a male inherits an X from his mother and a Y from his father.
When you order a DNA test from companies like Ancestry or 23andMe, they are testing your autosomal DNA ( the DNA in the 22 paired autosomal chromosomes). (23andMe also takes a cursory look at the X and Y chromosomes.) Autosomal DNA testing is really good for finding cousins—people who are related to you. That’s because people who are related share bits of DNA from their common ancestors. The more they share, the more closely they are related. This makes autosomal DNA testing ideal for genealogy, because it can be used to build or expand a family tree.
However, autosomal DNA testing has a limited reach, because the amount of shared DNA is reduced by approximately half with each generation. After 6 to 8 generations—200 years or so—the amount of shared DNA isn’t enough to reliably identify relatives.
Ancestry and other companies also use autosomal DNA testing to generate ethnicity percentages. These are estimates (i.e., educated guesses) of which countries and regions your ancestors came from. The estimates are only as good as the underlying data, and should not be taken as proven facts. The percentages are periodically updated by the DNA testing companies as their databases expand. (Click here to return to the main post)