How long is a human generation?

Today, with lager age at first birth ...

While you can age lagers, they are generally best served fresh. At least that's how we Generation Xer's drink it.

your story about meeting the former slave who remembered Lincoln getting shot is a lot better than my Dad's story about meeting a (the last?) veteran of the civil war in about 1950.

I find it helpful to consider what I think of as 'conversational generations'.
I had many conversations with my grandfather, who served in WW 1. It was incredible to me that living in New York City his whole life he could remember the first time he saw an automobile, left for France when there were only a few thousand telephones in the city, and experienced the introduction of radio not long after returning. He could remember his grandfather, a professional cavalryman who emigrated from Bavaria in 1861 and, needless to say, found employment immediately on arriving, leaving the Union Army as a Major at the end of the war. Surely that horse soldier would have remembered his own grandfather, who lived through, and possibly participated in, the great conflicts of the early Nineteenth Century. Thus I am three conversations from the Age of Napoleon, from Austerlitz and Borodino and the great upheavals of the Industrial Revolution; two conversations from Gettysburg and Cold Harbor and Emancipation and have myself heard my grandfather muse on the fall of the Kaiser and the fear he had of Atomic Bombs. A generation now afoot will hear from me how my father served on Okinawa, and went to his grave deeply in love with Quantum Physics, certainly a man of the Greatest Generation, though I'll point out that the cohort of that immigrant German might also claim that appellation.
Conversational Generations are long, history brief,violent, both turbid and illuminating, and it is those conversations that reassure us that if those people, blood of our blood and of no great difference in stature or wit, could endure and accomplish what they did then surely we Boomers and X'ers can likewise survive and thrive.
One day I'll calculate how many chats it would take me to get back to "So, Gaius Julius Caesar, what brings you here?"

This is an interesting post. There was a discussion on LanguageLog (which I no longer read because I get all the rudeness I need from other drivers) about generations. That conversation was started because of a quote from Rep. Michele Bachmann about the 21 generations that America has survived (or some such). There was a lot of discussion about what she could possibly have meant and what date she was aiming for in the past with her 21 generations. This problem was not solved before I left the conversation. I emailed her at her congressional email address to ask what she meant, but have not heard back yet.

@Mark, Attempting to translate deranged people from second hand stories may appear a fools errand to some, but sounds to me like Mrs. Bachmann must have meant 1492, because Native Americans aren't Real Americans and 21 x 25 years ago would be mid 1480s which is fairly close. Or she meant the signing of the constitution / first inauguration period from 1787-1789 and meant decades instead of generations and couldn't count as 210 years ago was off by a dozen years.

Then again, I'm probably giving her too much benefit of the doubt - after all, Columbus and the Pilgrims and the Founders all knew each other 500 years ago, right? Or maybe Jesus told her 21 was a good number 'cause it's half of the 42 generations between Jesus and who-cares in the Bible. I bet that's it.

LOL on the rudeness comment. You must live in Boston! Regarding Bachmann, if you don't live in her district she won't talk to you. That's her strongly implied policy.

Greg, that implies that if you live in her district, she will speak to you. I've seen plenty of people complaining that this simply isn't true.

I definitely did not mean to imply that! I have not heard specifically that she weeds people out based on party or voting or whatever. That's actually hard to do, but possible. It may be that she simply does not listen to anyone at all. I thought about noting this but they were only guesses on my part.

I didn't really expect a response from Bachmann, for a number of reasons. But I think most members of Congress don't pay much, if any, attention to correspondence from people outside their districts. I contributed to Al Franken's Senate campaign, but I don't live in Minnesota so I wouldn't really expect him to pay me much attention. And that doesn't bother me. He does a better job of representing my interests than my own state's two senators. And, by the way, I live in Georgia, but I have driven in Boston. There are differences - actually, great differences - but rudeness does not seem to be in short supply on the roads in either place.

I routinely write to members of congress, in both the house and senate, who do not represent my district or state. Usually, these are party leaders and committee chairs or committee members.

They all respond to specific communications, but usually it takes longer for those not directly connected by the vote. But they do respond.

Which reminds me. Check this out if you ever get a chance: The Lazlo Letters

It's encouraging that they respond to you. My own senators have responded, but it's usually clear that it's a canned response on a given topic. There is never even a pretense of trying to engage with what I have said, and there seems to be an underlying assumption that I agree with whatever they are planning to do.

Its usually canned for me too, but at least a response. I got Dayton and our congressmember who was at the time on the house Transport committee to communicate once and got an amendment. I call it "Greg's Law" though nobody else does, of course.

It is now a federal offense for a baggage handler in an FAA controlled airport to pilfer luggage. My reasoning: If a guy can steal something from a bag (such as my binoculars) they can be paid off to put something IN the bag.

You need to see the Lazlo letters. (There's a volume 2 as well)

R.I.P Frank Buckles, America's last surviving World War I veteran. 1901-2011.

Demographically speaking, a generation is the mean age of childbearing. It's also the time it takes for a population to increase by a factor equal to the net reproduction number. I could write some math here. Maybe I will on my blog where I have a LaTeX plug-in. The great demographer, Nathan Keyfitz once quipped that 27.5 should be considered a constant of nature as this is approximately the mean age of child-bearing in an amazingly broad range of populations (quite a bit more than either the standard 20 or 25 year benchmarks).

Another interesting usage of the term generation comes from mathematical epidemiology, where a "generation" refers to all people infected by a particular wave of an epidemic. All those people infected by the index case ("patient zero") are in the first generation, while all those infected by this group are in the second generation. If the number of infected individuals from one generation to the next increases, you have an epidemic. The growth rate of this early part of the epidemic is calculated from an object known as the "next generation matrix." I could do more math...

I recall from my Ancient History studies, c. 1960, that in Ancient Rome a festival was held every 110 years to mark a new age - on the grounds that anyone who had been alive in the previous period would now be dead. I believe one was held in Nero's reign. So your Long Generation has to be less than 110 years.
My great-great-grandmother arrived in Australia in 1858. Vivid tales of her adventures were passed on via her grand-daughter to her great-niece, my mother. When I checked what I could, much was provably true. Now I have told these stories to my grand-children (eldest is 22). That's seven genealogical generations, and maybe two Conversational Generations.
I get annoyed with folk who tell me that you can't trust oral history.

Oral history does need to be checked. The core may be true but the additions might not especially when not heard first hand. My great great grandfather supposedly rode on the first Stockton-Darlington steam train run (1825). We have other records that show he was in the right place at the right time (at school in Darlington and his cousins were financing the railway); however, it is unlikely that he did ride due to a death in the cousins' family the night before (none of them rode).

I always thought a 'generation' was 25 - 20 years is a 'score' (as in that speech that starts with Four Score and Seven years ago ...), although writing "4 generations and 7 years ago" would likely be punished by the English Squad.

I don't know if this really fits into the idea of generations, but late last year a 75 year old speaker I was listening to noted that he was only three life spans removed from the ratification of the US constitution. My dad is 75, and for some reason that observation has really stuck with me.

Jamie, thanks for chiming in. I had actually mean to include the demographic definition (average age of female giving birth) as part of the "biological" one ... (and ultimately as the basis for the "familial" definition) but it got lost in the fray. Good point about the epidemiological use of the term.

There was a time when it started to look like we could have LaTeX in our Scienceblogs.com comments but that seems to have been a pipe dream.

This was a wonderful read, Greg.

Doug, I think I have read this thinking along the same lines as you. It fascinates me to ponder the fact that there are people living today who can claim a grandparent born when George Washington was president. And it's odd coincidence that that grandparent was also a U.S. President.

Very interesting article. I'd been having a discussion with someone who thinks Hal Lindsey is a reliable source for various things. Back in the early 70s in his book, The Late Great Planet Earth, he said that a generation was about 40 years, and based on that and some jigsaw puzzle scholarship and interpretation of various passages, he said the return of Jesus would be within a generation of the leafing of the fig tree (i.e. the establishment of Israel in 1948).

Well the 80s came and went and no return (unless I was napping), so he changed it to 50 years (90s came and went), and recently has changed a generation to 60 to 70 years. Maybe he'll change it your Historical Long generation now?

btw, I pointed out that Lindsey himself, in a Christianity Today interview in the early 80s, said if his prediction didn't come to pass, he'd be a bum.

Anthea Fleming,

The term you're thinking of is saeculum, meaning, roughly, 'age' as in 'period of time'. If the starting point was taken as some important event (e.g. the founding of a city), a saeculum would have passed when everyone alive at that point had died. It's where we get our term 'secular' - because it measured time by worldly events, not heavenly ones.

They found some more: http://tinyurl.com/l3crte

very good friend, just what i was looking for. my wife has 5 living generation on her side and i have 4. i met my great-grandma and she saw Lincoln speak. what ever, i was thinking today- how many generations before man moves back onto a volcano or tsunami area? i lived through hurricane Andrew, did i already say whatever? john

devil anse hatfield died in 1921 my dad was born in 1903 and i was born in 1947, what generation from devil anse hatfield would i be?

Great explanation. I especially liked your concept of historical generation.

I am a hospice RN. I took care of a patient in 2009. She was 102 years old. She had been a probation officer in the '20s thru the 50's in Duluth Minnesota. Then had ran, with her sister, a B&B for many years. She had a clock above her bed. One day she asked me to adjust the clock to the current time. As I did she told me that the clock had been her great grandfather's clock. As I set the clock it suddenly occured to me that , at the very least, this clock had been purchased in 1834. 227 years before I was born!!! But for her it was just great grandpa's clock. She lived for a few more years with many more Superior stories to tell. I remained in awe of her clock and have taught many new hospice RNs to understand how really close history is to us.

my father had Parkinson's disease. My sister the third child born has a tremor in her hand now. We know the disease is hereditary, That it skips generations. My question is how long is a generation and is my sister included in this generation?

I didn't think it was hereditary

i think of a generation as very ten years in this sense:
Your generation is everyone that is five years older than you and everyone that is five years younger than you

type error: *every ten years

im 18 years old,what is my generation name? The list stopped at 1992. I was born in 95

Mabe

Someone who lived 100KYA would be how many generations removed from us, on average? 5,000? I'm thinking of Grandmother Human.

Yes I would say 5000.

I might out grandmother human way before 100k, though.

Some years ago I became fascinated by those generational family pictures that show the matriarch surrounded by her daughter, granddaughter and great-granddaughter. I wondered how many living generations could theoretically be in one of those pictures.

Assuming the youngest age for childbirth to be 12 and the oldest age before death to be 110 (both possible although uncommon), I figured you could have an eight-generation family.

This would be implausible in reality, because early childbearing age and long lifespan don't occur in the same populations.

Veronica, that is an excellent point.

There are many things that have a theoretical maximum but forces in play that make that maximum highly unlikely (I suppose the highest maximum might be infinity for some problems). Eight might be the theoretical maximum for human generations but it will, as you say, only very rarely be achieved.

The maximum that has happened so far as far as I know is six:

http://www.worldrecordacademy.com/human/most_living_generations_Gladys_…

Or seven, but no photo:

http://www.guinnessworldrecords.com/records-3000/most-living-generation…

Here's another six: http://io9.com/six-generations-of-the-same-family-in-one-photograph-786…

I recently performed an analysis of my generation within my mom's extended family (2nd cousins) and found the earliest born individual was born in 1928 and the latest, was 1973. That's a generational span of 45 years! I did the same analysis on my dad's side and found it to be nearly 40 years.
Is this to be expected within families?

My Great Grandfather was born in 1846, Grandfather 1868, Father 1916 I was born in 1945.

My grandfather was born in 1852, my mother, 1904, I was born in 1940, and my youngest child,, 1981.

I was researching this question because I was trying to get some idea of times related to the biblical claims of generations and the age of humanity subsequently correlated to the Genesis account. Unfortunately, I don't think this time frame of 25 years between generations would hold up to the biblical account.

First of all, I realized that we tend to measure everything in the present as though all life as it occurs today was always the same having the same life spans we witness today. This is, of course, the uniformitarian idea assumed under the evolution paradigm.

However, if one accepts the bible as a source of history, life spans differed quite markedly from those of the present. (And I am well aware that many people do not accept the bible as a true reflection of history which is a debatable point.) Many of the earliest ages reported in the bible were remarkably long and began to change markedly after the great flood.

Although, many people are skeptical of these time frames, I believe they could, in fact, be more valid than we have been led to believe. That is, longer life spans would make sense for a couple of reasons. They would also have an impact on generational calculations.

First of all, geneticists are noting that human beings have accumulated quite a few mutations over time (about 10 per generation are retained in the code according to the geneticist author of Genetic Entropy John Sanford.) These accumulations over time are reaching a point whereby they are having a direct impact on human health and quite possibly shortening our life span as well.

Additionally, during the early stages of human life on the planet, the code was cleaner (along with the food/water supply and natural conditions) with fewer mutations which would in turn also contribute to longer life spans.

A major catastrophic change like the global flood reported in Genesis would have had an impact on life spans due to the major transformations of natural living conditions on the planet after the flood. In fact, making the planet less hospitable particularly in the early centuries after the catastrophe with major climatic changes etc.

Biblically, life spans reported in the bible begin shortening to levels similar to those found today in the generations after the flood which would support those assumptions.

At any rate, the generation measurement level of 25 years, while accurate for todays time frames, would probably not be an accurate measure when stretched over the entire reported history of human kind.

So my idea to use the time measurements based on the accepted generational differences of modern day would probably not work when applied to the whole time span as reported in the bible because when people lived longer, they also married later and had children at much later ages as well.

Hence, with the realities of less mutations in the genetic code and changes in natural living conditions due to catastrophe, I realized that I would not be able to effectively correlate generations reported biblically with the age of human kind. Now, I wonder if anyone actually has accurately done that accommodating the life span changes mentioned above into their calculations?

MEASURUNG A GENERATION USING WORLD POPULATION DEMOGRAPHICS BY AGE, VITAL STATISTICS, GERONTOLOGY STUDIES, GOVERNMENT CENSUS AND THE CALANDAR YEAR OR HISTORICAL EVENTS
Today with well-kept vital statistics (birth and death certificates) along with technology, it is possible more than ever to measure, quantify and qualify populations and generations. In order to determine the length of a generation this study will use the calendar year, Pre-World War One, the World War One generations and a single family line of decent as an example.
The Calendar Year
A calendar year generation expires when the last oldest living person born in that specific year dies. It’s just that simple.
As an example; Emma Morano (2) was born November 29, 1899 and was considered to be the oldest verifiable living person in the world at 117 years 108 days old; as of March 17, 2017. She died on April 15, 2017, living 117 yrs. 137 days.
Secondly, Emma Morano had one other distinction; she was believed to be the very last verifiable person alive who was born in 1899. Keep in mind Emma Morano was once a new born baby. On Dec. 31, 1899 the last newest born baby (ies) and the oldest living person(s) marked the parameters of the generation of 1899, with everybody else, the entire world population, in between. They all continued to die off until the last one, Emma Morano was left. When she died, the generation of 1899 died. In fact all other generations in the past years 1898, 1897, 1896 etc. have also passed away.
Historical Events
The second way to mark a generation is by using an historical date. It works the same way as the calendar year except a specific historical date is used. When the last oldest living person, who was born the closest to the event, or on the day of the event, dies, that generation is dead. That’s it!
One question is: How many people left, from a given time period, amount to a generation? Is it 10,000; 1000; 100; 10 or just 1? There is no answer to this question. However, once the last living person dies, so dies the generation.
Because Emma Morano was born in Nov. 1899, before WWI began, she is part of the pre-World War One generation. Today there are still thousands of people who were born on or before July 27, 1914, the day before WWI began. Therefore the pre-WWI generation is still alive and will be for a short time until the last oldest living person, who must have been born on or before July 27, 1914 dies.
In other words, when the oldest living verifiable person is found to be born on or after July 28, 1914, the day World War One began, the pre-World War One generation will be dead; it’s the generation’s end.
Therefore to determine the length of a generation, all you have to do is keep an eye on who is the oldest living person, the date of this person’s birth and the event date in question.

Measuring a Generation-A World Population
It should be kept in mind that because WWI was a world event, the entire world population can be used to take the measurement of a generation. WWI was declared, erupting on July 28, 1914 a historically marked time period. Therefore, anyone born on and before July 27, 1914 is part of the pre-WWI generation. Most were also alive to experience WWI at that time. (If a person wants to be accurate to the extreme, you can use the very day, hour, minute and second before WWI was declared to divide the pre-WWI generation from the WWI generation. Just find the official document of declaration of war and check for a time stamp, if one exists.)
Statistical Data
It is possible to know how many people are still alive from that WWI area. According to the World Almanac there were approx. 1.6 billion people on the face of the earth about that time. As always the world population age ranged from the very oldest people to the newest born babes. Today in 2017 those newest born babes are some of the oldest people on the face of the earth
In 2014 it was estimated by the United States that there were 450,549 (1)(5) people around the world who were 100 years old or older. Statistically, of all those who live to be 100 years old, only 1 out of 1,000 will live to be 110. That means at the 110 year mark from the date of July 27, 1914, there will be at best approximately 451 people round the world who will be 110 years old and older.
According to supercentenarian studies, (supercentenarians are people 110 years old and older)(3) once people hit the age of 110 they will die off at 2 out of every 3, until full mortality is reached at around 114 to 116 years of age, with possibly, not always, only a very few, 1 or 2 or so, going beyond that age. Very few make it to 117 or older. In fact from 1955 to the time of this writing, March 2017, only six verifiable people have lived to be 117. Only 2 lived beyond that age, one to 119 and the other, Jeanne Louise Calment who lived to 122 years, 164 days. Most of the oldest living people died at 114 years of age. (Keep in mind researchers are unable to determine whether they have all the information at hand and so use best figures at that particular time.)
The question is how long will they live and so mark the end of the Pre-World War One generation? Only time will tell. (One point of note: the Spanish Influenza took many lives and may have cut short the length of time of the oldest living people from that pre-WWI generation, the WWI generation and the post-WWI generation. Nevertheless as always, when the last one dies, regardless of their age, the generation dies.)
The WWI Generation
WWI ended on November 11, 1918. Therefore the generation of WWI was composed of those people living when WWI broke out and those who were born during WWI. (July 28, 1914 to November 10, 1918.) Once the last pre-WWI generation member dies, the next generation to become the oldest living people on the face of the earth will be those who were born during WWI. They will die off a few years after the pre-WWI generation. Anyone born after Nov.10, 1918, is not of the WWI generation but they are part of the post-WWI generation.
This being said, people live through various events in their lives. Someone who was part of the pre-WWI generation, if they lived long enough, was also part of the WWI generation and the post-WWI generation. If they lived even longer they were also part of the pre-WWII generation and the WWII generation. Some of them actually participated in WWII. (Note: the post-WWI generation can also be known as the pre-WII generation depending on how someone wants to present an idea.)
A Step Down
A generation can also be used to mean a step down or the next step in the line of one’s decent. As an example, a married couple who were born in the pre-WWI era has a baby born the day after WWI began. That baby cannot be part of the pre-WWI generation. But it is a part of the WWI generation as are the parents. Generations cannot perpetuate but events can go on a long time after a generation has died such as some wars which have historically lasted hundreds of years.
Consider the seasons of the year. Summer, fall, winter and spring are specific. They each are definite marked time periods starting on a given day every year and ending on a given day every year. Spring does not and cannot perpetuate or overlap into summer regardless of the temperature or world events. So it is with a generation, it is marked either by a specific historical date or calendar year. When the last oldest living person dies, the generation dies. Generations come and go just as spring time and the other seasons come and go. Multiple events can go on within the life of a generation. Likewise the reverse is true, past wars of history have prolonged for hundreds of years, while multiple generations have been born and died within those war years.
There may be some claims that generations are built around historical events. However, this claim brings up the question, when does the generation end? How many years after an historical event must be counted to still mean a specific generation is in existence? It becomes arguable and hazy and not worth discussing as it yields no certain answer. It is much more specific and exact to count those who were born after an event ended as the post- generation of such an event.
Use of the Word Generation
BEWARE: It’s important to know how the word generation is being used within the context of the speaker or writer to understand the specific meaning of the word. This report doesn’t cover every use of the word. See a dictionary for more information.
Unverifiable Ages
At this point take note we have been dealing with verifiable birth records and not unverifiable claims of a person claiming to be older than those whose ages are verifiable. How these unverifiable individuals should be viewed depends upon other factors or questions. Here are some examination questions to use to determine if such a person’s age can be accepted. (4)
1)Is the person male or female? Usually women live longer than men. So the odds against male claimants being the age claimed is reduced but not out of the question.
2)Is the person from a developed country or a third world country? In third world countries there is usually little to no health care and more lawlessness. A person’s life is cut short by these and other factors.
3)Is the person literate? If the person is not literate, they probably can’t count. Nonetheless to be certain, ask the person if they can count? If so, ask when did they learn how to count? Was it late in life? If late in life this isn’t a valid test. But if a person claims they learned to count at an early age, use this test:
As an example, if a person claims to be 150 years old, ask the person to count from 0 to 150. If that person misses half the numbers than its probable that person is 75 years old or close to that age. In other words, however many numbers they miss during the count, subtract that from the age they claim.
4)Does the claimant know what a calendar is? Do they know how to use it? If they never or sporadically had a calendar, then it’s much easier to lose track of time and they may have guessed at their age now and then.
5)Does the person smoke, chew tobacco, use drugs for recreation, over eat or engage in any habits that cut a person’s life short? In developed countries these habits, despite medical care, do indeed cut one’s life short; so it becomes very questionable if a third world claimant is the age they claim.
6)Does the person have any health problems? As an example, a weak heart. This in itself will affect a person’s memory as a weak heart doesn’t pump enough blood to the brain and so affects the memory.
In conclusion, anyone who can’t verify their claims to be older than those who can validate their age is probably not accurate and should be held highly questionable and probably discounted.

References:
(1)World Population by Age and Sex - U.S. Census Bureau
https://www.census.gov › ... › Data › International Data Base

(2) List of the verified oldest people - Wikipedia
https://en.wikipedia.org/wiki/List_of_the_verified_oldest_people

(3) Supercentenarian - Wikipedia
https://en.wikipedia.org/wiki/Supercentenarian

(4) Typologies of Extreme Longevity Myths - Hindawi
https://www.hindawi.com/journals/cggr/2010/423087/
(5) (http://www.un.org/en/development/desa/population/theme/ageing/index.sht…). Their current estimate for world population 100+ in the year 2015 is 451000
See Also:
Centenarian - Wikipedia
https://en.wikipedia.org/wiki/Centenarian

Guinness World Records, see oldest living person.
(https://esa.un.org/unpd/popdev/Profilesofageing2015/index.html). If you have further questions on this information, you can contact Population Division directly at population@un.org.
"Table C - World's Oldest Person (WOP) Titleholders Since 1955". grg.org. Retrieved 27 July 2015.