Smith DNA Project Community Forums

Studies of average generation length

Many recent studies of average generation lengths have challenged earlier assumptions:

• Tremblay and Vezina studied 100 catholic French Canadian families of 1850-1990s, finding average generation lengths of 34.5 years for males and 28.9 years for females.^[10] They noted that some of the earlier genetic studies were based on mtDNA studies only, which may explain some of the bias now apparent in their average generation lengths.
• Helgason et al studied Icelandic genealogies of 1742-2002 and found average generation lengths of 31.9 years for males and 28.7 years for females.^[11]
• Matusmura and Foster studied 1805-1974 genealogies for 225 families in North Greenland and found average generation lengths of 32 years for males and 27 years for females.^[12]
• Jack Fenner undertook detailed analysis of many pre-2005 genetic and genealogical studies and found average generation intervals amongst hunter-gather societies of 31.5 years for males and 25.6 years for females (although with a large variance), amongst less developed nations of 31.8 and 28.3 years, and amongst developed nations of 30.8 and 27.3 years respectively. He recommended the use of 31 years for males and 25 years for females.^[13]
• Donn Devine, after reviewing published research on Quebec, Icelandic, and Botswana Dobe !Kung hunter-gathererer populations, recommended using 33 years for male-line generations and 29 for female lines. Comparing his own known ancestry, he found close agreement, with average generation lengths of 34 years for males and 29 years for females.^[14]
• King and Jobling adopted 35 years for English males.^[15]
• The pedigree of Confucious over 80 generations, recently revised, has an average (male) generation length of 32 years.^[16]
• The earliest pedigree in the Cruwys surname DNA project shows average intervals of 30-35 years for males.^[17]
• In the Irwin DNA Project nine Irwin paternal pedigrees dating from between 1323 and 1660, largely Scottish, with a wide range of socio-economic backgrounds, have intervals of between 31 and 38 years.^[17]
• The MacDonald surname DNA project recommends 31 years for males.^[18]
• The Williams surname DNA project finds 28-33 years for males.^[17]
• Tetushkin suggests using 31-32 years as the average generation length for males, and a little less for females.^[19]
• Katherine Borges gives examples of average generation lengths of 18.2 years, 43 years and 58.5 years.^[7]

Vol. 5 No. 1 Jan/Feb 2012 From the Director - The Hamster Wheel of Generation Length Besides mutation rate philosophies, there's not much else that can make you go round and round like a hamster on a wheel to nowhere other than debating average generation length. Many people think the average generation length is 25 years while others put the number at 30 or even 35 years. The topic often surfaces on genealogical mailing lists and forums and even more so in the genetic genealogy community since generation length is applicable to mutation rates. Really now, what does it matter? Unless you're a geneticist it doesn't matter what the average number is. What does matter for you is what the average number is for your family. In my family, we have a long generational length on my direct paternal line back to 1710. All of the males in my line were born when their fathers were in their 30's and 40's. My paternal grandfather was born in 1894 and I was born when my father was 43 and this ended up putting quite a damper on the length of time I had with my grandfather. (He died when I was four). Albeit, long generation length is great from a DNA perspective. In theory, because the less generations you have from the common ancestor, the less likelihood for mutations to randomly occur. Since I mentioned my direct paternal line, that may be associated with Y-chromosome DNA testing, but my families' long generational length has also been advantageous with autosomal DNA testing as well. My father has a living first cousin born in 1920 who matches Bill Hurst. Bill and I have known for years that we share a common BARKSDALE ancestor who was born btw. 1664-1670 and with the onset of autosomal DNA testing, matching DNA is visible between Bill and my first cousin, once removed. However, with myself being born one generation later, the matching DNA segment is not visible between myself and Bill at the matching thresholds set by the DNA companies. Determining an average number for generation length is not going to be "one-size-fits-all" for everyone. Baroness Elliot of Harwood had a generation length of 58.5 years while Augusta Bunge's family has a generation length of 18.2 years.1 To reiterate, the only number for generation length that matters is your own number which can be determined here. The average generation length for my paternal line is 43 years. So the next time you see the generation length debate raging on a mailing list or forum, save yourself some time by skipping that hamster wheel to nowhere. -Katherine Borges