Introduction to the Mayfair Witches Family Tree

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Genealogy and Genetics

The Mayfair family tree presents a unique problem when it comes to genealogy and genetics. Often, what happens when two people are too closely related to produce offspring that cannot survive to reproduce. It's a pileup of too many of the same genes that results.

However, this does not mean it would be impossible for two people who are a little more distantly related to produce offspring that can survive to reproduce. That threshold is generally considered to be at second cousins or more distant degrees of relatedness. Well into at least the 19th century, it was still legal in the United States for first cousins to marry, which many did.

What does this mean for our ancestry and our genetics? What effect does it have on genetics and does this happen in real life? To help at least try to answer some of those questions, I decided to put together a brief tutorial of family trees that contain a lot of pedigree collapse. And of course, I will explain what I mean by pedigree collapse...

Average Amount of DNA Inherited From Ancestors

Parents 50%

Grandparents 25%

Great Grandparents 12.5%

2nd Great Grandparents 6.25%

3rd Great Grandparents 3.13%

4th Great Grandparents 1.56%

5th Great Grandparents 0.78%

Likelihood of Detectable DNA In Common

23andMe AncestryDNA Family Tree DNA

2nd Cousin or Closer >99% 100% >99%

3rd Cousin ~90% 98% >90%

4th Cousin ~45% 71% >50%

5th Cousin ~15% 32% >10%

6th Cousin or Further <5% <11% <2%

The Taltos and the Theory of Evolution

The averages in the charts are averages only. They are estimates based upon only one line of descent/one common ancestor. Obviously, family trees like that of the Mayfairs are going to have vastly different averages of shared DNA because of how many lines of descent any given Mayfair will have.

Mona Mayfair is described (by herself and others) as a "twentyfold Mayfair", meaning twenty different lines of descent. But what does that mean, exactly?

In recent years, there has been a huge uptick in the amount of interest in our family trees, our genetics, and what they tell us about genealogy. We have learned a lot of surprising things. We've learned these things through what is usually referred to as "genetic genealogy".

The second chart above gives averages from three different DNA testing products. They each have their own testing thresholds. Each of them can provide valuable information about our DNA.

While this site is not about true crime, I will say this: genetic genealogy has had an incredible impact on cold cases. Crimes committed decades ago have been solved and unidentified persons have finally been identified, many times after decades of being known as Jane or John Does with unique additional names to distinguish one Doe from another. One example: Jane "Arroyo Grande" Doe, whose name, Tammy Corrine Terrell, was finally returned to her after 41 years.

So, how can we apply what we know now to the study of the Mayfair family tree?

The charts above come from this online article on Family Tree Magazine

DNA Q&A: Genealogical vs. Genetic Family Trees

Terms to Know

Something I think is important to have a basic knowledge of when studying family trees like this one is a couple of terms.

This is the part where I have to advise caution. Family trees that show considerable pedigree collapse due to either or both of the terms I will provide definitions for can be an extremely sensitive subject in a lot of ways.

So I want to make it clear that this study of the Mayfair family tree is one that describes characters in fiction. It is here to help further examine the genealogy of the Mayfair Witches as part of the plot in the novels based on what is known about genealogy and genetics. It is for this and no other reason that this is discussed on The Mayfair Witches Parlor.

Pedigree Collapse

In genealogy, pedigree collapse describes how reproduction between two individuals who share an ancestor causes the number of distinct ancestors in the family tree of their offspring to be smaller than it could otherwise be. (Wikipedia)

Pedigree Collapse on Wikipedia

Endogamy

The cultural practice of mating - usually in the form of marriage - within a specific social group, religious denomination, caste, or ethnic group, rejecting those from others as unsuitable for marriage or other close interpersonal relationships.

A long term pattern of endogamy in a region may increase the risk of repeated cousin marriage during a long period of time, referred to as inbreeding. It may cause additional noise in the DNA autosomal data, giving the impressions that DNA matches with roots in that region are more closely related than they are. (Wikipedia)

Endogamy on Wikipedia

Incest

noun

noun: incest

sexual relations between people classed as being too closely related to marry each other.

the crime of having sexual intercourse with a parent, child, sibling, or grandchild. -From Oxford Languages

Genealogy of Cousins

Cousins are the type of relative we all have more than any other. They can also be the most complicated to trace both in genealogy and in genetics.

Please see the content advisory on this page of the Parlor before proceeding: The Lineage of the Legacy Witches

Before proceeding to the content on this page of the Parlor, it is strongly advised that you review the tutorial provided on Introduction to the Mayfair Witches Family Tree

We don't simply have first, second, third cousins, but a mind boggling assortment of cousins often referred to as x many times removed. It's one of the questions people ask the most: what is the difference between, say, a second cousin and a first cousin once removed?

Hopefully, the animations below, made from a video I made on the subject recently, will help answer that question if you are unsure. However, the family tree discussed on this site is one that contains people who are cousins by more than one line and varying degrees of relatedness.

At a casual glance, endogamy is most definitely well practiced in the Mayfair lines. But what does that say about the genetics of these cousins?

I have the average percentage of DNA shared by cousins on this page as well, which is, of course, a starting point. It also assumes that two people are cousins only through one line. So, if two Mayfairs are both first and third cousins...

The general rule of thumb, using the numbers as averages, is that the more times you are related to someone, the DNA tends to calculate accordingly.

Now, what the Sam Hill?

Let me put it this way. You could have a cousin who, on paper, is an eight cousin as well as a fifth cousin, and so on. But comparing DNA, you and this person appear to be a lot more closely related than you actually are.

Two of my 4th Great Grandfathers were of a set of triplets

Let's use one child for each of my 4th Great Grandfathers

First Cousins

The child of each of my 4th Great Grandfathers are 1st cousins

Second Cousins

Each of the 1st cousins has a child

The children of each 1st cousin are 2nd cousins to each other

First Cousin Once Removed

So, what is a 1st cousin 1x removed?

We would need to go back to one of the 1st cousins. The 1x or once removed part is because that is the number of generations removed from the two 1st cousins they are. So, the "1st cousin" is determined by the one closest to the common ancestor, and the "1x or once removed" part is how many generations there are between that cousin and the 1st cousin.

The Mayfair Punchline...

Now, about these two second cousins...

They married and became my 2nd Great Grandparents

...or Not.

This was very common at the time. 2nd cousin marriages are legal to this day, and considered safe as far as reproduction is concerned.

When you look at family trees where cousin marriages were common, it's important to look at it in the context of the era and society they lived in. This is where the word "endogamy" comes in.

It is important to distinguish this term from "incest". Today, an incestuous union is one where two people are too closely related to reproduce without negative consequences. Everyone has dominant AND recessive genes without exception. When two people are too closely related to reproduce, the likelihood of producing offspring with too many of the same recessive genes.

Not all recessive genes are deleterious by themselves. However, there are plenty of them that if they accumulate too much, will have a disastrous effect on those who come from unions like that. With the Mayfair Witches, it is this pileup that Lasher is "engineering": a witch who will be able to pass the genes he needs to be born in the flesh.

Endogamy can be hard to explain, but there are usually socioeconomic reasons for it. It's often seen in royal families, and nobility. It was how families made sure their wealth, power, authority and all the things that come from those were kept within families.

In rural, heavily isolated and very small societies, you will see endogamy. Island societies are one example. Another well known example is early Colonial Americans. Mayflower passengers, Massachusetts Bay Colony, Jamestown... In fact, I have seen discussion in recent years about how endogamy might have played a role in the Salem Witch Trials. Specifically, what might have truly led to this literal witch hunt.

America at the time was not yet the United States. It was still under the throne of England. This was a very small, isolated population of people on an enormous continent. Choices were limited, so you either married a cousin or you didn't marry at all. After a few generations of this, you begin to see the effect of endogamy on the family tree: pedigree collapse.

At that point, 1692, it's easy to imagine the disputes that might have arisen. Disputes as to who has a rightful claim on property, that sort of thing. Even with the Mayfairs, you can see a lot of endogamy going on whether or not Cortland Mayfair was both the father and great grandfather or Rowan Mayfair.

It is my understanding that AMC's Mayfair Witches is on its way to a second season. A lot of the topics I've been discussing on this part of the Parlor are most deeply explored in Lasher, the second book in the Lives of the Mayfair Witches. Dolly Jean Mayfair seems to have helped to nudge in the direction of explaining how a family of human witches would be able to produce a being that looks like an exceptionally tall human with DNA, a giant helix, that is only about 40% similar to humans...