Anniversaries force us to take a moment to consider what is truly extraordinary even while being utterly routine. “I’m so appreciative of all of you being here on this occasion," said Grandfather Facer. "It’s merely a hundred years."

SALT LAKE CITY — Joseph Elmer Facer, my maternal grandfather, turns 100 years old today. The last of my living grandparents, Grandfather Facer gathered last Wednesday just north of here, in Bountiful, with all six of his children (all still living), and many of his 25 grandchildren and 39 great-grandchildren, to celebrate his becoming a centenarian.

Thinking about my grandfather on the occasion of his birth on August 10, 1914, caused me to reflect on the length of generations, and the role that significant anniversaries play in our lives.

Grandfather Facer is a native of Brigham City. His own maternal great-grandfather was James Gray Willie, the leader of one of the two troubled handcart companies caught in the 1856 early winter storm. Growing up in a farming culture, Grandfather was an Aggie at Utah State University. He lived his professional life as a banker in Colorado, the home of my maternal grandmother’s family, where all of his children were born. He made loans on livestock and agricultural property throughout the Great Plains West. With the passing of my grandmother more than 25 years ago, he’s spent these many long later years of his life in Colorado and in his home state of Utah.

Our society has a pretty simple way of measuring a year: The length of time that it takes the earth to circumnavigate the sun. But measuring the length of time that it takes a human generation to turn over isn’t nearly as straightforward.

For example, generations can overlap, as they do among Grandfather’s descendants. At Wednesday’s gathering, the oldest of Grandfather’s children was 72; the youngest is 56. The oldest among the grandchildren is 49; the youngest is 12. The oldest of the great-grandchildren is 19, while the youngest is one week old. The third and fourth generations have begun to coincide. This will be even more pronounced when the fifth generation arrives.

Although there is a span of time for each generation within the family, the centerpoint of any given generation can be ascertained. Yet genealogists haven’t done a good job keeping track of generational time.

Take the traditional generational average of 25 years, or four generations per century. This rule of thumb isn’t right.

Donn Devine, a genealogical consultant in Wilmington, Delaware, and archivist with the Catholic Diocese there, became skeptical of this number when he began to explore commercially available genetic testing through Family Tree DNA several years ago. “The 25 years that people used for the length of a generation causes a major miscalculation,” Devine told me, “and yet that number is still being used with no thought as to where it came from.”

Devine investigated the findings of demographic researchers, and compared them to his own family records from 1700 to 2000. He measured a generation from a father’s birth to the birth of his middle son, or from a mother’s birth to the birth of her middle daughter.

Devine also measured generations from the marriage date of parents to the marriage date of parents’ children. Whether from a 1979 study of the !Kung people in Namibia and Botswana, a 2000 investigation of Quebec families, or a 2003 project with the Icelandic deCODE genetics database, the length of a generation turned out to be remarkably consistent on average: Three generations per century – 33 years – for male lines, and 3.5 generations per century – 29 years – for female lines.

Father-to-son generations are less frequent than mother-to-daughter generations because males are likely to marry and have children later than females.

Celebrating a generational change every 33 years, or every 29 years, doesn’t quite have the appeal of a big round number like 50 years or 100 years. In fact, our culture inescapably looks back in time to these important, landmark anniversaries.

Just in the past year, for example, we’ve noted the 50th anniversary of Martin Luther King Jr.’s March on Washington, the assassination of President John F. Kennedy and the signing of the Civil Rights Act of 1964 by President Lyndon Baines Johnson. This month marks the beginning, 100 years ago, of World War I. In Sesquicentennial time – between four and five generations ago, on average – we have entered the final year of the U.S. Civil War. The re-election of Abraham Lincoln is by no means assured, and Sherman’s March across the south has yet to take place.

Anniversaries force us to take a moment in time to consider what is truly extraordinary even while being utterly routine.

Standing to address all his many offspring last Wednesday, Grandfather said, “I’m so appreciative of all of you being here on this occasion. It’s merely a hundred years.”

Drew Clark can be reached via email:, or on Twitter @drewclark