The Mayfair Witches Parlor

Mayfair 500: How Cousins Are Made

• Come Together
  The Mayfair Witches Family Tree The Mayfair Witches Family Tree Tutorial Mayfair 500: How Cousins Are Made Mayfair Relatedness: Rowan Mayfair Mayfair Relatedness: Michael Curry Mayfair Relatedness: Mona Mayfair Mayfair Relatedness: Merrick Mayfair
• Genealogy of Mayfair Cousins
  Genealogy of Cousins First Cousins Second Cousins First Cousin Once Removed Likelihood of Detectable DNA In Common The Mayfair Punchline... ...or Not.

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

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

Each of the 1st cousins has a child

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

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.

Relationship	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%

Now, about these two second cousins...

They married and became my 2nd Great Grandparents

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...