I have the genealogy from my father’s paternal line.
There are 9 generations between my son, born in 2013, and his ancestor, John, born in Culpeper County, Virginia in 1753.
That’s a far more pedestrian pace, at 28.89 years per generation.
I see it didn’t preview.
The more recent one using mutation rates:
Thanks for providing this. I’ll be sure to read it.
Interestingly enough, that’s pretty close to the 25-year definition that demographers use for some things.
Yes, looking at my English farmer ancestors, what data I can find - the groom was typically much older than the bride, 8 to 20 years. Without any other data, I suspect this came down to the son being essentially the hired hand on dad’s farm until dad was ready to retire and let him “own” the farm. Once the man had a decent stable “income” so to speak, his own farm, then he was marriage material. The woman was marriage material as soon as she was of marriageable age, late teens.
So if we’re being sexist and considering the age of the lineage more through the male side (the family name) then generational length will be longer than through the female side(s).
It seems to me by the early 1800’s this difference disappeared - since a man could establish a working job and stable income earlier, independent of his father’s farm or business, while women were generally expected to spend more time in school than before and with better standards of living, families found less urgency to “unload” newly mature daughters - who also had earning opportunities of their own in industrial England.
Yeah, this isn’t going to be straightforward. My family has pretty good records going back ~1000 years, at least in the male line. I’m in the 32nd generation of descent from the founder of my line (so the ~33 years is pretty good), while I know there are people currently living who are in the 37th/38th generation of descent (closer to ~26 years per generation). And that’s for people who are all descended from the same person.
There are plenty of variations and being descended from a string of 4th or 5th children can really affect things down the road.
Even in the shorter range there are significant variations. My first cousin once removed is my age - but my grandparents were her great-grandparents - three generations for her (her greatgrandfather’s birth to her birth is 87 years - but that’s only two generations for me (my father was the youngest of a large family and had children late))
Precisely my point. In individual terms, “generation” is meaningless. Some families have absurdly large or small parameters for a meaningful definition, but the whole of humanity over a longish period of time will establish some sort of norm, which we can use as a yardstick for one’s own family.
My mom was one of seven children, the youngest of the bunch, so all my cousins are older than I am–the range from oldest to youngest is 30 years, practically a generation in itself. But since all of my first cousins share two grandparents, I have one clear commonality with people, now mostly dead, much older than myself.
I’m not so sure.
The general nature of statistics is that some distributions have single tall narrow peaks. For distributions like that, the average = arithmetic mean has decent predictive or explanatory power.
Other distributions have a very wide range with a broad plateau and nothing that resembles a central peak. For a distribution like that the arithmetic mean is certainly a well-defined mathematical construct, but has just about zero explanatory or predictive power.
“Standard deviation” is the common metric for the peakiness of a distribution. And even that falls apart in the presence of a multi-peaked distribution. Which is what I suspect age-at-offspring birth is.
My maternal grandfather met my maternal grandmother when she was eight. Waited till she was fifteen to marry her. She gave birth fifteen times over eighteen years. Thirteen children survived. My mother was her eleventh child.
That data may confuse matters. Consider that before the availability of reliable birth control, women started giving birth nearing adulthood and continued doing so until they either died (in childbirth?) or reached menopause.
Access to birth control likely drive the average age down as women could limit their pregnancies to early adulthood, the “family raising” years. .
In the 70s, women start having careers in large numbers, and start delaying childbirth to get college degrees and start those careers. Having fewer children per family and starting later would push the age upward.
I’m pretty sure those are the factors driving the trend.
How that affects some nebulous concept as “a generation” is left as an exercise for the reader.