How Long is a Generation?

Updated May 6, 2019

This article was scientifically reviewed by YourDNA

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On the surface, asking the innocuous question of “How long is a generation?” may seem like it has an easy answer to it.

But in Western cultures, depending on who you ask and how they define what a generation is, you could get one of several different answers.

What's in this Guide?

Disclaimer: Before You Read

It is important to know that your genes are not your destiny. There are various environmental and genetic factors working together to shape you. No matter your genetic makeup, maintain ideal blood pressure and glucose levels, avoid harmful alcohol intake, exercise regularly, get regular sleep. And for goodness sake, don't smoke.

Genetics is a quickly changing topic.

In high level terms, a generation is defined as a body of individuals who are born and living in about the same time in society. The accepted amount of time varies depending on the source and can range from 20 to 35 years or thereabouts.

As lifestyles change and lifespans lengthen, the amount of years in a generation also tends to change over time as well. In past centuries, when lifespans were shorter, more generations existed in a single century (the generally accepted amount was four).

But as times have changed, the number of generations in a century has also changed as well (it is moving closer to three).

Different researchers and cultural anthropologists may also apply different standards when trying to define a generation as well.

For example, a Biological generation is the transition from a parent to an offspring. A biological generation does not have a standard length. It simply means you are in one generation, your mother and father are in a different generation, and your child is in a different generation as well.

A Familial generation is used based on when an actual birth took place within a family. A few centuries ago, the accepted and often used value was about 20 years, meaning that as many as five familial generations could exist in a single century.

However, as older birthrates for women changed, the recommended estimate for a Familial generation is now 25 to 30 years.

A Cultural or Societal generation is a cohort (several people born in a specified time range) with an identifying name attached to it. These are widely used and accepted throughout society.

Recent generations in the Western world have become well known by the names that the media and advertising industries have given them:

  • The Lost Generation roughly describes those who fought in World War I. Members of this generation were typically born between 1883 and 1900.
  • The Greatest Generation are those who include veterans who fought in World War II. They were born from around 1901 to 1927 and came of age during the Great Depression.
  • The Silent Generation were born from approximately 1925 to 1942. Most of the people in this generation came of age during the Korean War and Vietnam War.
  • Baby Boomers, also known as the Me Generation, were born mostly from 1946 to 1964. A post WWII baby boom made them the largest demographic segment for many years.
  • Generation X, or Gen X, followed the baby boomers. Demographers and researchers typically use starting birth years ranging from the early-to-mid 1960s and ending birth years in the early 1980s.
  • Xennials are the micro-generation of people between Generation X and Millennials. They were born between the late 1970s and early 1980s and are described as having had an analog childhood and a digital adulthood.
  • Millennials, also known as Generation Y were typically born starting in the early 1980s through mid 1990s to early 2000s as ending birth years. In 2019, Millennials are expected to surpass the Baby Boomers in size in the U.S., with 72 million Boomers and 73 million Millennials according to Pew Research.
  • Generation Z people were born after the Millennials. Demographers and researchers typically use the mid-1990s to early-2000s as a starting birth years.

How Many Years is 3 Generations?

It depends. Generally, three or four generations span 100 years, but depending on a number of factors, that same amount of time could produce as little as two generations or as many as five generations.

The average span between one generation and the next is about 25 to 30 years, so a safe answer would be 75 to 90 years.

Keep in mind that this is only an average and when researching specific family history, additional documentation such as birth records, personal family history, public records and so forth should be accessed to give the most accurate personal indication of how long three generations would be in a particular family.

How Many Years is 10 Generations?

Again, it depends on what the accepted number of years that a generation is. The most commonly accepted value is four generations per century, meaning that tracing backward by 10 generations would find ancestors who lived about 250 years ago, in the middle of the 18th century.

However, as generations, lifespans and lifestyles continue to morph, the trend has been more toward an accepted three generations per century. This would mean that an ancestor could be traced as far back as the late 1600s.

Much of this is based on individual circumstances and to support and further pinpoint how long 10 generations is within a particular family, additional documentation and evidence to support ancestry should be used to get a more exact answer.

How Can DNA Tests Help Determine Generations?

Genealogical DNA testing is used to determine information about personal ancestry by comparing one person’s results with others from the same lineage or ethnic groups.

These types of tests are different from those used to determine if a person is a genetic carrier for specific types of diseases and conditions.

Studying the DNA collected from a simple cheek swab, researchers can look at a person’s Y-DNA, which is passed on to them from their father and analyze the sample for distinctive markers that are DNA code for specific characteristics. The DNA evidence provided by these markers allows a person to show the migration routes of paternal ancestors going back several generations.

The same type of testing can be done when analyzing mitochondrial DNA on a mother’s side.

You can find out which of over 200 populations you are genetically most similar to and what proportions of your ancestry come from the other continental level groups.

What are Male-Line Generations?

In genetic genealogy, male-line generations are known as patrilines to describe the line of descent through the all-male line. It is also sometimes referred to as the agnatic line.

In genetic terms, patrilines correspond to the transmission of the Y chromosome from one generation to the next. In genealogical terms, patrilines will correspond to the transmission of surnames from generation to generation.

However, there may be instances where a non-paternity event disruption has taken place and when this happens the genealogical patriline will not be the same as the genetic patriline.

What are Female-Line Generations?

In genetic genealogy, male-line generations are known as matrilines to describe the line of descent through the all-female line. This is also known as the agnatic, enatic, uterine or umbilical line.

Matrilines are passed from one generation to the next through the transmission of mitochondrial DNA. Males and females both can receive mtDNA from their mothers, but only women can pass it along from generation to generation. Men are not able to do so.

How are Generations Studied?

Generations are studied in a number of ways. From a macro point of view, cultural scientists study larger trends and patterns of groups of people born at approximately the same time.

On a personal level, there is a growing interest in learning about a person’s family history. This is done on both a genetic and on a genealogical basis, researching public records and personal family historical documents as well as documenting the biological component as well.

To get the most accurate and thorough analysis of a person’s genealogical DNA, there are three principle types of DNA tests that are available.

Autosomal DNA testing will provide a large number of DNA test results and matches indicating a significant number of people that a tested person may be related to. It is more useful in estimating ethnic mix and by itself is not an accurate indicator of a person’s personal genealogy.

Because the amount of DNA that is passed from generation to generation is random, accurate conclusions using only autosomal DNA can only go back just a few generations.

Y-chromosome testing and mitochondrial DNA (mtDNA) testing are much more reliable and can go back many more generations except that they will give considerably fewer DNA matches.

The Y-chromosome is passed along only from a father to a son because women only have X chromosomes in their 23rd pair of chromosomes. This means a male-line ancestry can be traced using the Y-chormosome because it is transmitted from father to son nearly unchanged.

To trace the direct maternal line between two suspected relatives, mtDNA is studied. Mitochondrial DNA is transmitted from mother to child, so a direct maternal ancestor can be traced using mtDNA.

Mutations in mtDNA are rare, so a perfect match found to another person’s mtDNA indicates there may be a shared ancestor dating back as many as 50 previous generations.

It should be noted that as physical and biological sciences become more sophisticated as data becomes more readily available, that genealogical conclusions about relationships may also change as well. Better and more voluminous evidence means more accuracy can be achieved in the study of generations.

What is Epigenetics?

Epigenetics is the study of biological mechanisms that switch genes off and on. In simplified terms, this means that human cells contain DNA, which are the instructions required to direct a cell’s activities.

DNA is made up of four bases. They are adenine, cytosine, guanine, and thymine, commonly abbreviated as A, C, G, and T. There are about 3 billion bases, and in these bases are about 20,000 genes.

Genes are specific arrangements of bases that provide instructions on how to make proteins. These proteins are complex molecules that trigger various biological functions to carry out life instructions.

This is the central thesis of molecular biology and genetics.

Epigenetics affects how genes are read by cells and whether those cells should produce the proteins necessary for life instructions.

Epigenetics determines a cell’s specialization. In other words, it determines if a cell is going to be a skin cell, a hair cell, a liver cell, a bone cell, and so forth.

A fetus develops into a baby and is given individual traits through gene expression, which means a gene is active, or silencing, which means a gene is dormant.

Environmental stimuli can also cause genes to be turned off or turned on. This means what you eat, who you interact with, how you sleep and even how you age can cause chemical modifications that can turn genes off or on over time.

This also means that genes can be switched from a normal and healthy state to the opposite, and this is when diseases such as cancer or Parkinson’s or any number of other conditions can develop.

Epigenetics is what makes each person unique. Different combinations of the 20,000 genes in our body will cause our hair to be one color, influence the color of our skin and eyes, and even contribute to certain personality traits, among many others.

Epigenetics holds fascination among the scientific community because theoretically, if scientists can figure out which genes, or combinations of genes, to turn off and on, they may be able to find cures for many diseases such as cancer, obesity, heart disease and many other ailments.

How Can DNA Differ from Generation to Generation?

Environment and lifestyle choices can influence epigenetic changes from one generation to the next. Depending on choices and changes a person makes in their life, it is possible to change a person’s DNA in ways that may be reflected in their life and also in future generations to come.

Studies have shown that prenatal and early postnatal environmental factors influence the adult risk of developing various chronic diseases and behavioral disorders.

For example, research has shown that a mother’s exposure to pollution could impact her child’s susceptibility to asthma and the intake of vitamin D affects placenta functioning. Others studies have shown that a father’s diet could have an impact on an unborn child’s mental fitness and epigenetic marks as well.

Epigenetic marks are more stable during adulthood but can still be modified by lifestyle and environmental choices throughout a person’s life. Epigenetic changes can also be reversed.

There are a number of examples that show how different lifestyle choices and environmental exposures can alter DNA and play a role in determining health outcomes.

Pollution has become a significant focus in this research. Scientists have discovered that air pollution can alter DNA and increase a person’s risk for neurodegenerative disease.

Researchers have found that a ketogenic diet – consuming high amounts of fat, adequate protein, and low carbohydrates – increases an epigenetic agent naturally produced by the body.

As scientists unlock these answers, in the future an epigenetic diet may create an optimal food regimen that will impact a person’s epigenetic health.

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