Discussion:
Evaluating pedigree collapse
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Ian Goddard
2020-01-21 12:05:09 UTC
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I have a family tree whereby a group of siblings have four lines of
descent from the same couple. For three of these there are 7
generations and for the other there are 6 generations. The 7 generation
descent would give 128 distinct genealogical roles at this level and the
6 generation descent would give 64. In fact I find 10 individuals
filling 24 of these roles so there are 14 "missing" ancestors due to
pedigree collapse.

I wanted to express this 14 as a proportion of the whole. I decided
that an appropriate figure for the whole would be 3/4 of 128 and 1/4 of
64, 112 in total so that 1 in 8 potential ancestors are lost due to
pedigree collapse. Does this seem a reasonable way of expressing it?

Ian
Evertjan.
2020-01-22 10:34:14 UTC
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Post by Ian Goddard
I have a family tree whereby a group of siblings have four lines of
descent from the same couple. For three of these there are 7
generations and for the other there are 6 generations. The 7 generation
descent would give 128 distinct genealogical roles at this level and the
6 generation descent would give 64. In fact I find 10 individuals
filling 24 of these roles so there are 14 "missing" ancestors due to
pedigree collapse.
They are not really missing,
as it is the norm in an ecological niche called earth.

When the niche gets smaller, called isolation,
the phenomenon gets more pronounced,
like among sects, monoglots or on remote islands.

<https://en.wikipedia.org/wiki/Ecological_niche>
Post by Ian Goddard
I wanted to express this 14 as a proportion of the whole. I decided
that an appropriate figure for the whole would be 3/4 of 128 and 1/4 of
64, 112 in total so that 1 in 8 potential ancestors are lost due to
pedigree collapse. Does this seem a reasonable way of expressing it?
"Pedigree collapse"?

Sometimes the German word is more elegant:

"Ahnenschwund"

Never heard of the Dutch version:

"Kwartierherhaling"
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)
Graeme Wall
2020-01-22 11:18:11 UTC
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Post by Evertjan.
Post by Ian Goddard
I have a family tree whereby a group of siblings have four lines of
descent from the same couple. For three of these there are 7
generations and for the other there are 6 generations. The 7 generation
descent would give 128 distinct genealogical roles at this level and the
6 generation descent would give 64. In fact I find 10 individuals
filling 24 of these roles so there are 14 "missing" ancestors due to
pedigree collapse.
They are not really missing,
as it is the norm in an ecological niche called earth.
When the niche gets smaller, called isolation,
the phenomenon gets more pronounced,
like among sects, monoglots or on remote islands.
Doesn't need to be remote islands, I have pronounced examples in my
wife's family in both North and South America. Both as a result of the
families being there in early colonial days.
--
Graeme Wall
This account not read.
Evertjan.
2020-01-27 13:03:46 UTC
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Post by Graeme Wall
Post by Evertjan.
Post by Ian Goddard
I have a family tree whereby a group of siblings have four lines of
descent from the same couple. For three of these there are 7
generations and for the other there are 6 generations. The 7 generation
descent would give 128 distinct genealogical roles at this level and the
6 generation descent would give 64. In fact I find 10 individuals
filling 24 of these roles so there are 14 "missing" ancestors due to
pedigree collapse.
They are not really missing,
as it is the norm called earth.
When the niche gets smaller, called isolation,
the phenomenon gets more pronounced,
like among sects, monoglots or on remote islands.
Doesn't need to be remote islands,
What's unclear in my "like"?
Post by Graeme Wall
I have pronounced examples in my
wife's family in both North and South America. Both as a result of the
families being there in early colonial days.
What's unclear in my "more pronounced in [] ecological niches"?
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)
knuttle
2020-01-22 14:23:50 UTC
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Post by Ian Goddard
I have a family tree whereby a group of siblings have four lines of
descent from the same couple. For three of these there are 7
generations and for the other there are 6 generations. The 7 generation
descent would give 128 distinct genealogical roles at this level and the
6 generation descent would give 64. In fact I find 10 individuals
filling 24 of these roles so there are 14 "missing" ancestors due to
pedigree collapse.
You do not mention the sex of the member of each generation. If you mean
by missing that you can find no one of the family name to fill the
missing position, then it can easily be explained by the ratio of males
to females. If there are several generations where mostly females are
born in our society the family surname is likely to disappear for that
generation.

My grand father had two boys, the boys had five boys. Only two had one
boy each, and the third generation of two boys had no boys. So for that
line the family surname disappears.
Ian Goddard
2020-01-22 20:37:19 UTC
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Post by knuttle
Post by Ian Goddard
I have a family tree whereby a group of siblings have four lines of
descent from the same couple.  For three of these there are 7
generations and for the other there are 6 generations.  The 7 generation
descent would give 128 distinct genealogical roles at this level and the
6 generation descent would give 64.  In fact I find 10 individuals
filling 24 of these roles so there are 14 "missing" ancestors due to
pedigree collapse.
You do not mention the sex of the member of each generation. If you mean
by missing that you can find no one of the family name to fill the
missing position, then it can easily be explained by the ratio of males
to females.   If there are several generations where mostly females are
born in our society the family surname is likely to disappear for that
generation.
My grand father had two boys,  the boys had five boys.  Only two had one
boy each, and the third generation of two boys had no boys.  So for that
line the family surname disappears.
I put "missing" in inverted commas. They are the difference between the
actual number of people as opposed to the number there would be if there
was no pedigree collapse. For example one couple appears 4 times; if
they didn't there would be 3 other couples in that generation. I count
those 3 couples as 6 "missing" people.

There were no step children involved so they're "missing" in couples.
the number of "missing" males and females is balanced. Not all lines
have been resolved so it's not impossible that there was more collapse,
in fact there were a pair of brides with the same surname. For one of
them I can't get back beyond her father and for the other the number of
known baptisms is a bit sparse so it's possible they could be 1st or 2nd
cousins. However for the purpose of calculation I've assumed that all
the collapse is known so my 1 in 8 is in fact at least 1 in 8.

Ian
Evertjan.
2020-01-27 13:14:34 UTC
Permalink
Post by Ian Goddard
Post by knuttle
Post by Ian Goddard
I have a family tree whereby a group of siblings have four lines of
descent from the same couple.  For three of these there are 7
generations and for the other there are 6 generations.  The 7
generation descent would give 128 distinct genealogical roles at this
level and the 6 generation descent would give 64.  In fact I find 10
individuals filling 24 of these roles so there are 14 "missing"
ancestors due to pedigree collapse.
You do not mention the sex of the member of each generation. If you
mean by missing that you can find no one of the family name to fill the
missing position, then it can easily be explained by the ratio of males
to females.   If there are several generations where mostly females
are born in our society the family surname is likely to disappear for
that generation.
My grand father had two boys,  the boys had five boys.  Only two had
one boy each, and the third generation of two boys had no boys.  So
for that line the family surname disappears.
I put "missing" in inverted commas. They are the difference between the
actual number of people as opposed to the number there would be if there
was no pedigree collapse. For example one couple appears 4 times; if
they didn't there would be 3 other couples in that generation. I count
those 3 couples as 6 "missing" people.
There were no step children involved so they're "missing" in couples.
the number of "missing" males and females is balanced. Not all lines
have been resolved so it's not impossible that there was more collapse,
in fact there were a pair of brides with the same surname. For one of
them I can't get back beyond her father and for the other the number of
known baptisms is a bit sparse so it's possible they could be 1st or 2nd
cousins. However for the purpose of calculation I've assumed that all
the collapse is known so my 1 in 8 is in fact at least 1 in 8.
There are two types of "missing"

1 having ancestors by multiple ancestorial pathways.
[this is the norm in an ecological niche]

2 having ancestors that are not known by documentation
or trusted oral tradition.
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)
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