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.


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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.

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

Lutz, Catherine. Reading National Geographic

Teh Wiki. Generation.

Teh Wiki List of generations.

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One thought on “How long is a human generation?

  1. If you accept 20 years as the historical average for Familial Generations then we are only about 600 generations removed from the generally accepted start of agriculture which resulted in “civilization”. If you accept that then it’s only taken us 600 generations to go from nomadic hunter gatherers to potentially destroying most life on the planet. (which is why I scare quoted civilization)

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