We often use the term "generation" in genealogy, as well as in historical studies and in social discourse. We even give names to generations: Baby Boomers, Generation X, "The Greatest Generation." Sometimes we ascribe general qualities and values to persons born during certain generations. Witness the television commercials today that target aging Baby Boomers with rock songs and psychedelia!
What is the average length, in years, of a generation? I have not yet heard a definitive answer. Historians generally define a generation according to events that bookend a period of births. Some genealogy sources that I have seen claim a generation is twenty years, while others have said twenty-five to thirty or more. In an individual family, a generation is the number of years between a parent and a child. However, even in one nuclear family, a generation will differ according to whether one uses the mother or the father as the yardstick, and what child is being used as measurement.
I've been interested in the subject of the length of generations ever since I discovered that my great grandfather Richard Large was born in 1826. I am fifty-seven years old, and there are not many people my age whose great grandfather was born so very long ago. My Large family's average generational length is very long because my father was the youngest of ten children, and his father was youngest of eleven. Richard Large was 54 when his wife gave birth to my grandfather!
The answer is an important one in genetic genealogy because the rate of mutation is tied to generational length. The International Society of Genetic Genealogy (link: ISOGG) has helpful information regarding the topic, which is quite beyond my ability to explain--my last biology class in DNA was back in the day when we filled out charts for blood types!
Sometimes it can be helpful and interesting to know your own family's average generational length. The length can perhaps unveil a familial or historical pattern in your ancestors' lives. For an excellent guide to calculating your family's average generation, follow the instructions in this EHOW.COM article:
EHOW.COM HOW TO CALCULATE GENERATIONS