Welcome Cousin! Are We Related? How So?

Welcome! If you are reading this page, you are either a DNA match to one of the kits that I manage, or you have found a common ancestor in one of the family trees that I have published. We might be blood relatives.

Then again … we might not be relatives at all. I probably sent you a link to this page because usually my first reply to new genealogy contacts has been an email with some subset of what is contained herein. Please read the whole thing through.

If you are a very experienced genealogist who has experience with DNA genealogy, you can skim through it.  You know exactly why I asked you to read it. You can also jump forward to get to my information. Otherwise, please take the time to read and digest … then get back in touch with me.

The DNA Testing Genealogy Exploding Head Syndrome

I have a problem … I have been contacted by hundreds of people who were told by one of the DNA testing services that we are matches. My backlog of emails that I have not answered at all is close to 100 people deep and some are almost three years old. Often I am contacted with a message, like “Ancestry says that we are 2nd to 3rd cousins … can we explore this?” or “Do you have any of these family names in your family tree?” or “My great-grandfather comes from Czechoslovakia … do you have any information about this family from there?”

There is a corresponding problem, for people who are trying to contact their matches (myself included). You send out very polite inquiries to your matches, with plenty of data to help them work out your match, trying to find a common connection, and you never get a response from most of them.

Both problems have a common cause … too much data, not enough information and very little guidance from the DNA testing companies. Unfortunately, their marketing sets an expectation that with the tiny bits of information available from DNA testing services that two people can connect their family trees, figure out their shared lineage, build out large parts of each other’s missing ancestry, and happily invite another 30 people to the next family reunion.

When I do respond to these first contacts, I usually end up having to explain how difficult and inconclusive genetic genealogy really is. I am not a professional, but I have been working this for a couple of years now, and it is not easy to draw meaningful conclusions more than 2 generations out without large numbers of family tested and a well-developed family tree going back more than 4 generations.

The most heart-breaking inquiries are from adoptees who are searching to learn their true family history. They are hoping to make contact with someone who will give them the puzzle piece that will connect them to their past, and I really wish that I could give it to them.

Exponential Relative Numbers

My genealogy database, as of this writing (September 2019) contains 2,157 individuals. Many of these are not blood relatives because I document close spousal families and descendent trees as well. That is a very small database in genealogy research terms.

My DNA analysis database contains 237,400 matching “relatives” (the software designer’s choice of terms).  Many of those are duplicated on the order of 4 or 5 records per actual DNA matching person.

Assume, for a moment, that every ancestor in your family tree was an only child and each couple had exactly one child.

Relationship People in your tree
0  Yourself 1
1  Parents 2
2  Grandparents 4
3  Great-grandparents 8
4  Gg-grandparents 16






Add that up and you have 31 people in your family tree in four generations. Genealogists usually want to have all the names, birth, death and marriage dates and places of each person in their table, if possible. Do you know all that about those 31 people? If so, you are off to a great start. You also probably don’t have many DNA matches because you are your only possible cousin.

Let’s make things slightly more realistic. Let us assume that every couple in your family tree has/had exactly two children. Let us revisit the table and include our cousins.

Remember that your first cousins share a common grandparent, your second cousins share a common great-grandparent and your third cousins share a common great-great-grandparent with you.

Relationship name in your tree uncle / aunt first cousins second cousins third cousins total down
0  You / Siblings 2  0 4 16 64 86
1  Parents 2 2 8 32   44
2  Grandparents 4 4 16     24
3  Great-grandparents 8 8       16
4  Great-great-grandparents 16         16
total across 32 14 28 48 64 186






So for finding first cousins, with only two children per couple, a family tree of fourteen people is adequate to find all relatives. They are highlighted in yellow. To find second cousins, you need a family tree of fifty people to find all relatives. Thos numbers are highlighted in orange and yellow. Do see where this is going? It’s not going to be pretty. To find third cousins you need a family tree of 186 people.  Those are the numbers in blue, orange and yellow.

Now, modern families are relatively small, 2 or 3 children per couple. Go back fifty or sixty years, and 8 to 10 children per couple was not uncommon. Not all of the children survived to child-bearing age, but these numbers get very big very fast.

How Reliable Are the DNA Estimates?

It depends. If you have Ashkenazi Jewish (AJ) ancestry … not very much beyond the second generation. Ashkenazi Jews historically have been an endogamous population. It was very unusual to marry outside the faith, and those who did were shunned from the community. People did not travel very far as they do now. The movement of Jews was also severely limited by where they were allowed to live and travel. As a result, the community of available spouses was very small. It was inevitable that blood relatives would inter-marry. All efforts were made to avoid marrying closer than second cousins to reduce deleterious genetic effects. However any intermarriage in an earlier generations completely mangles the statistical models that are used to estimate how closely two persons are related based on matching DNA segments. If your testing service says “2nd to 3rd cousin” you need to be thinking “4th to 5th cousin and maybe also a 6th cousin thrown in there.”

My DNA is 98.6% AJ, based on the models used by 23andMe, and nearly 100% according to AncestryDNA‘s model. If you have a DNA match to one of the kits I manage, you are matching AJ DNA. That means that we are already farther apart than you have been led to believe.

Here is a very good article about the problem: “No, You Don’t Really Have 7,900 4th Cousins:  Some DNA Basics for Those With Jewish Heritage” by Jennifer Mendelsohn. She explains it much better than I can.

Getting Started

If you are new to genetic genealogy, you need to learn a lot to make sense of it. You also must have a family tree going back multiple generations to make use of it for finding distant relatives. If your family tree is sparse in the first three generations away from yourself, that is a much better place to be spending your time researching.

Sharing Your Family Tree with Me

There is no harm making initial contact with your matches. Be aware that the first thing that anybody who knows what they are doing is going to ask you for, if you hear back from them at all, will be something like: “Please send me a copy of your family tree. I need the following information for all your blood relatives that you know:

  • Name, birth date, birth place, death date and death place of each person.
  • Spouse names, marriage dates and places for each marriage, or partnership and approximate date ranges if there may have been a birth resulting (e.g. for adoptees seeking birth family).
  • Linking of parents to children.

That is the data that is included in a family tree. They can be displayed in many different formats. What is important is that the data is known … at least, parts of it.

That is the first thing that I am going to ask you for.

If you have an online genealogy that is freely accessible, or if you have it in a machine-readable format, like a GEDCOM file, that will help. My genealogy software can read GEDCOM files and I can do some analysis on my local computer. There are also online tools that can compare GEDCOM files to find possible common matches.

If your online family tree obfuscates living persons for privacy reasons, you may have to send me some supplemental information to get me from the names of your living ancestors to the people who are visible in your family tree. Please read this post if you or your family members are still using a “mother’s maiden name” as a security identifier – then go fix that problem ASAP.

Entering the DNA Rabbit Hole

You will also have to learn a little bit about genetic genealogy. Not a lot. You don’t have to learn organic chemistry or molecular biology.  If you did OK in high school biology you can grasp this stuff with a little studying.

You do have to understand what terms liks SNP and cM and MRCA mean.  You should know the difference between atDNA, mtDNA, XDNA and YDNA and how each one is relevant to genetic genealogy.

The best place to get started is on the web site of the ISOGG, the International Society of Genetic Genealogy. They have a getting started page that links to many good resources. Bookmark that page now. Start to explore the wiki and the other pages there. I did say that this is a rabbit hole, like in Alice in Wonderland. It may be a while before you hit bottom.

The following genetic genealogy information that will help me to analyze our common ancestry. For each DNA sample or kit:

  • Which service was the match on?
  • What is the full name or identifier on that service of the person whose DNA kit matched?
  • Is the DNA kit for that person accessible on multiple DNA services? If so which ones?
  • If the kit is on multiple services, which ones are original sequences and which are uploaded kits?
  • Which of the DNA kits that I manage match? I manage DNA samples for myself, my mother and my sister. Each has a slightly different email address. You might have matched one, two or three kits.
  • Have you uploaded this DNA kit to GEDMatch? If so, please let me know the identifier or the email address you used to identify that kit.
  • Are there other known family members who have also tested their DNA? We will want all the above data for each of them that match one of my kits.
  • Have you successfully matched with any other relatives who are in a confirmed position in your family tree?

My Information

It would be incredibly rude of me to ask you to send me lots of information and not tell you how to find mine. I have created a web page that contains links to my family trees online. It also contains the identifiers of the DNA kits that I manage.

Please feel free to contact me . I try to respond to all messages in a timely fashion.

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