Understanding complex family relationships and implexes in genealogy

Discover how to identify and calculate complex family relationships and implexes in genealogy

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Understanding family relationships is essential for any genealogist, especially when dealing with relationships other than direct lines (parents, grandparents, children). Studying the extended family reveals relationships that can sometimes be difficult to name. Terms like first cousin, second cousin once removed, implexes, or cousin by marriage are often encountered, and these can be confusing.

Degrees of relationship: civil and canonical law

The term "degree of relationship" refers to the genealogical proximity between two people. It is calculated differently depending on the context:
In French civil law: to connect two people, you count the number of generations linking the first person to the common ancestor, and then from the common ancestor to the second person.

In canon law: only the number of generations separating the common ancestor from the people concerned is counted.

For example: two first cousins (children of two brothers or sisters) are fourth-degree relatives in civil law, but second-degree in canon law.

Calculating degrees of relationship

To accurately calculate advanced degrees of relationship, you must distinguish two types of genealogical relationships: direct line (ancestors/descendants) and collateral line (siblings, uncles, cousins). In everyday French genealogy, civil law calculation is generally used.

In the direct line (parent/child, grandparents/grandchildren), simply count the number of generations between the two people.

For example:

• Parent – child: 1st degree
  
• Grandparent – grandchild: 2nd degree
• Great-grandparent – great-grandchild: 3rd degree.

For collaterals (siblings, cousins…), the method is as follows:

1. Go back to the common ancestor
2. Count the generations separating each individual from this ancestor
3. Add the generations for each “trip” (round-trip).

For example:

• Brother and sister: 1 generation to the common ancestor (parents), 1 generation to the other – total: 2nd degree
• Uncle/aunt – nephew/niece: 1 generation to grandparents, 2 generations to the nephew – total: 3rd degree
• First cousins: 2 generations each (up to grandparents) – total: 4th degree
• Second cousins: 2 generations (one side up to grandparents) + 3 generations (the other side to great-grandparents) – total: 6th degree.
  

For two people A and B, the degree of relationship (in the collateral line) = number of generations from A to the common ancestor + number of generations from B to this ancestor.

Cousins: first cousins, second cousins, marriages

There are several types of cousins:

• First cousins: children of brothers and sisters, they share the same grandparents, so they are 4th degree. These are called "first cousins" because the term comes from the Latin germanus (brother/sister).

• Second cousins: each child of two first cousins is said to be "once removed" relative to the other, sharing the same great-grandparents (so 6th degree). In English, we call this a "second cousin."

• Cousin by marriage: this refers to a family relationship arising from marriage, without blood ties. For example, the respective children of two couples united by a second marriage become cousins by marriage.

Implexes and consanguinity

The implex appears in a genealogy when two ancestors appear several times in the tree, due to a marriage between relatives, often cousins. This phenomenon was common in areas with low mobility, especially in rural areas. Calculating the implex allows you to estimate the degree of consanguinity in a family line.

The implex corresponds to the difference between the number of distinct real ancestors and the number of theoretical ancestors at a given generation, due to marriages between relatives (consanguinity).

Implex calculation formula

- Implex rate (percentage of duplicates) = (N - R) / N

N = number of theoretical ancestors at the considered generation (for example, generation 4 = 2^4 = 16)
R = actual number of distinct ancestors found at the same generation

This rate is generally expressed as a percentage (multiply the result by 100).

Concrete example:
If at the great-grandparent generation (generation 4), a person should have 16 theoretical ancestors but only has 14 (due to implexes):

- Implex rate = (16 - 14) / 16 = 0.125 = 12.5%

A high rate indicates a high number of consanguineous marriages in the line.

There is also the implex index:

- Implex index = (actual number of distinct ancestors) / (theoretical number)

This index ranges from 0 (all ancestors are the same, theoretical case) to 1 (no implex).
These calculations are only reliable if all ancestors at the generation in question are known.

In conclusion, understanding complex family relationships and mastering the calculation of degrees or implexes greatly enhances your research and the accuracy of your genealogical tree. This is the key to faithfully reconstructing the history of each family and avoiding common errors when entering data.

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