How long is a human generation?

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How long is a generation, you ask?

Short Answer: 25 years, but a generation ago it was 20 years.

Long answer: It depends on what you mean by generation.

In US-biased Western culture there is a Biological Generation, the Dynamic Generation, the somewhat different Familial Generation, what is sometimes called a Cultural Generation but that should really be called a Societal Generation, and then there is the Designated Generation and finally, the Historical-Long Generation. You will find some of these terms identified on genealogical web sites, Teh Wiki and elsewhere, and some of them are introduced here. (References provided below.)

More broadly speaking, humans have identifiable meaningful generation-related terminology and cultural concepts in many but not all societies, and when it does occur, it is more common to find the concept in age-graded societies or societies in which marriage arrangements are fairly strictly enforced (or at least strongly hoped for) by the ascending generation.

A Biological Generation


…is simply the unscaled transition from one parent to one offspring. In humans, the Biological generation does not have a standard length but there are limits. So you are in one generation, your mother the previous, your child the next one after you, etc. regardless of when any of you were born. As long as your Uncle Willard does not marry your Sister Betty Jean, this is not complicated; This is what people often mean when they use the term “generation” but not what they mean when they ask the question “how long is a generation.”

A Dynamic Generation


…is a concept used by anthropologists but not usually with this term. This is similar to the biological generation but applied more broadly across a group of people. You (Ego) relate to everyone else of your age as being in your generation (your siblings, your parents siblings children, etc.). The first ascending generation (your parents and those in their generation), the second ascending generation (grandparents and their generation) etc. go one way in generational time. Going the other way, your children and their generation are the first descending generation. Your grandchildren and their cohort members are the second descending generation. Etc.

Those methods of reckoning generations have to do with the relationship between people. Another reason to reckon generations is either to do demographic (or economic) analysis or to test and analyze genealogies. For this you want to know how long a dynamic generation (or a biological one) usually is. For instance, a genealogist wants to know this: From the point of view of some long-dead relative, is the time span between the birth date of a grandparent and the birth date of a great grand child … thus, the span of time of four complete generations … reasonable? If such a span is 200 years, that means that an average of 50 years time passed from birth of a person to that person giving birth to the person in line. Implausible. If the total span is 40 years, that means ten year olds were having babies (on average). Also implausible. Either way, some part of the hypothetical genealogy is messed up and it’s back to the church records, vital statistics, and Mormon database for you. This is a Familial Generation.

In the “old days” (whenever that was) people often used the value 20 to represent Familial Generations. So, a person born on the first day of a century may well have had a great great great grandparent born around the beginning of the previous century. Today, with lager age at first birth for women being the rule, we tend to see 25 years as the recommended estimate for Familial Generations.

A Cultural or Societal Generation


…is a cohort (a bunch of people born during a specified range of time) with a name that has some sort of meaning to those who use it. The following are widely recognized, given here with the midpoint of the generally accepted range of birth dates:

  • Lost 1914
  • Greatest 1923
  • Silent 1935
  • Baby Boom (Boomers) 1955
  • Generation X 1968
  • Generation Y 1975
  • Generation Z or I 1992

(See comments below for people fighting about these names and dates. I accept Teh Wiki as the final word on this, so I take this list as perfectly accurate and complete.)

Several things are noticed in this list. The first three relate to major historical events (World Wars, the Great Depression) while the later ones are vague, stupid, and obviously little more than lame attempts by people who wish they were part of a generation to name themselves. This leads to the X and Y generations to be floating in broader time ranges (see Teh Wiki) and very arguable. The Z generation is clearly an afterthought. I assume everyone was so focused on the Millennium that they forget to be in a generation for a decade or so, and then had to catch up.

Some of the more primitively sexy and exotic tribal cultures of the world have a strict age grading system. This is where individuals are in a specific age-defined stratum, and there are several strata. Often there are different age-grades for males and females, and often there are more age-grades for males than females. Individuals of a particular age grade always X and never Y (fill in cultural prescriptions for X and cultural proscriptions for Y). The Pokot of East Africa are one example. These age grades can be termed Designated Generations and include not only groups like the Pokot but also Americans who have very strongly age-graded designations.

Among the Pokot males of a certain age wear a certain hairdo. Males of a certain generation get married. All the important things you can do or not do are defined by one’s age grade. As young men age they want to move to the next age grade, and often take serious risks to do so. In one Pokot group, the boys of one age grade would typically wear the hairdos of the Ascending Generation. Males in the Ascending Generation would then beat the crap out of them. When the beatings became too common and severe (sometimes deadly) the Ascending Generation of the Ascending Generation (the “Elders”) would declare that it is time for everyone to move up one generation, and a ceremony would be held.

In that particular group the ceremony applied to many different villages, and representatives from each village had to bring to the major chief’s village one head of cattle. The cattle were all slaughtered and the fresh meat laid out on wracks to be guarded from lions and hyenas overnight by the chief. If any of the meat was taken by predators, the chief was fired and a new chief appointed, everyone was sent home and were required to return with a fresh head of cattle, and the ceremony was re-started with the new chief. But I digress.

The Historical-Long Generation is my own invention. This is the period of time that is just short enough for a person to have a conversation with another person about shared memories where those memories are separated in time by the maximum amount possible for our species. Let me explain further:

Just today, the last surviving US veteran of World War I died. When I was a kid, I went to (or marched in) parades in which there were lots of veterans. Most vets in the parade were of World War II. Korea was not ever represented. The Viet Nam Vets were busy in Viet Nam being Viet Nam soldiers, so they were not in the parades. But World War I was represented by the grandpas and there were a lot of them.

And, leading all of the veterans in the parade was this one guy who looked quite dead, eyes closed, not apparently breathing, wearing a 19th century Slouch Hat and covered with a blanket and slumped in wheel chair pushed by members of the VFW Ladies’ Auxiliary, and he was the only remaining veteran in town of the Spanish-American War. I know he was not in fact dead because he was in the parade several years in a row. That war was in 1898, and the parades I remember must have been from the mid 1960s. I assume he was a drummer boy, perhaps 10 or 11 at the time of the war. The last surviving vets from Civil War were similar: Boys who served in the military as aides or drummers. The point is, one could argue that a historical-long generation is about a century, because that old guy and I share involvement in an event … marching in those parades … that link two memories, the parade and the war, which were about 100 years apart.

I have an even better memory. The Emancipation Proclamation was signed on Januray 1st, 1863. When that happened, a toddler who’s last name was Alexander and who was born as a slave in the Carolina’s became free. Later, his family moved to Albany, New York. In around 1968 or 1969, my father asked me to accompany our congressman, Representative Samuel A. Stratton (famous for introducing the bill to give us Monday Holidays, I am told) to an old tenement building in “Teh Ghetto” and bring him up to the third floor to meet Mr. Alexander, the now old former infant slave. I did so, and we all chatted for a while. I was about ten, and Mr. Alexander was closer to 110. He had memories of the assassination of Abraham Lincoln that were similar to my memories of the assassination of John F. Kennedy: Vague, mostly about the aftermath and not the event so much, but seemingly real. We shared memories that were a century apart in time, and in this case, interestingly parallel.

So, the Historical-Long generation is a century. If you meet me and shake my hand, you are shaking a hand that has shaken the hand of a man who was an American slave. Meaningless, yet profound.

Fischer, Michael D. Web site about calculating kin.

Fox, Robin. Kinship and Marriage: An Anthropological Perspective (Cambridge Studies in Social and Cultural Anthropology 50)

Lutz, Catherine. Reading National Geographic

Teh Wiki. Generation.

Teh Wiki List of generations.

_____

Other posts of interest:

Also of interest: In Search of Sungudogo: A novel of adventure and mystery, which is also an alternative history of the Skeptics Movement.

Comments

  1. #1 The Science Pundit
    March 1, 2011

    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.

  2. #2 rob
    March 1, 2011

    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.

  3. #3 JB
    March 1, 2011

    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?”

  4. #4 Mark P
    March 1, 2011

    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.

  5. #5 Miles
    March 1, 2011

    @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.

  6. #6 Greg Laden
    March 1, 2011

    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.

  7. #7 Stephanie Z
    March 1, 2011

    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.

  8. #8 Greg Laden
    March 1, 2011

    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.

  9. #9 Mark P
    March 1, 2011

    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.

  10. #10 Greg Laden
    March 1, 2011

    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

  11. #11 Mark P
    March 1, 2011

    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.

  12. #12 Greg Laden
    March 1, 2011

    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)

  13. #13 Nyarlathotep
    March 2, 2011

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

  14. #14 Jamie
    March 2, 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…

  15. #15 Anthea Fleming
    March 2, 2011

    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.

  16. #16 Erp
    March 2, 2011

    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).

  17. #17 MadScientist
    March 3, 2011

    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.

  18. #18 Doug
    March 3, 2011

    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.

  19. #19 Greg Laden
    March 3, 2011

    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.

  20. #20 Brett
    March 4, 2011

    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.

  21. #21 Dan
    March 5, 2011

    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.

  22. #22 mad the swine
    March 5, 2011

    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.

  23. #23 Andrew
    March 10, 2011

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

  24. #24 john essmaker
    March 14, 2011

    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

  25. #25 roy hatfield
    silver springs nevada.
    July 17, 2012

    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?

  26. #26 Ariane
    January 25, 2013

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

  27. #27 deb
    Woodbury Mn
    March 16, 2013

    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.

  28. #28 ditdo
    home
    March 29, 2013

    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?

  29. #29 Patricia
    March 29, 2013

    I didn’t think it was hereditary

  30. #30 PatrikG
    milwaukee wi
    May 17, 2013

    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

  31. #31 PatrikG
    milwaukee wi
    May 17, 2013

    type error: *every ten years

  32. #32 Achii
    Usa
    September 18, 2013

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

  33. #33 Greg Laden
    September 18, 2013

    Perhaps you are from the “nameless generation”?

  34. #34 Achii
    USA
    September 19, 2013

    Mabe