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How long is a generation?
This page describes results of an analysis of generation lengths in trees submitted to the project.
We do not claim this as a representative sample, but results do agree with
others' findings and may shed a bit more light than general statements.
The time unit that DNA respects is transmission events or generations, in
which DNA is passed from parent to child. Yet, DNA matches often relate to
the number of generations of separation between two living people descended
from a common ancestor. Or, they may be described in terms of cousinship --
2nd, 3rd, 4th, etc.
Neither generations of separation or cousinship, of course, directly say when
that ancestor may have lived. Genealogists, and especially genetic genealogists,
have tried to estimate years per generation as a means of estimating those
dates. There is much controversy about which estimate is best.
Taylor Family Genes reviewed 325 lineage trees submitted to the project for
publication. Of those, 245 (75%) contained sufficient data to enable analysis.
We used the birth year of the earliest known (most distant) ancestor
(abbreviated EKA) and number of generations from him to the submitting
descendant, along with the submittal date of the tree. Submittal date minus EKA
birth yielded the number of years included in the tree and the result was
divided by number of generations to get an average generation length in the
This is the "Raw" number. The "Adjusted" number assumes the submitter was
born 55 years before submittal; we did not collect the birth dates of the
submitters. In effect, the adjustment subtracts 55 years from the most
recent generation. .
Here are summary statistics from that analysis:
n = 267
EKA Birth Year
The above statistics suggest that the "Raw" figures are too high and the
"Adjusted" figures too low. A reasonable compromise seems somewhere between the
Notice the wide disparity from one family to another as displayed in this histogram
Focusing on the 20-25 year range:
Notes on the Data
Although taking some precautions to limit errors, we can not vouch for accuracy of the submitted data. For example,
one tree with
an EKA birth of 1610
listed only four generations since -- for an average
generation length of 90 years! We believe at least five generations
were omitted and a more credible average generation length in this family is 44 years
"raw", 38 "adjusted".
We did not calculate generation lengths within paternal genetic families.
We draw these conclusions from the data:
Generation length is highly variable from one family to another.
A "most probable" estimate has low confidence of being correct. It
has, at best, only 22% probability of being right within ±1 year and 54%
within ±3 years.
Confidence ranges are large. A 90% confidence interval ranges from 22 to