Simple Question

[dprice]

I'm sure that this question has been addressed, but entering the term "generation" gives me 192 threads to search through... .

Could someone please clarify the number of years that constitutes a "generation?" I had always thought it meant 25, but after some searching I saw numbers from 20 all the way up to 36! Is there a generic 'standard' for this?

Thanks for the help.

D. Price

[Jim Honeychuck]

You must choose. In a calculation in a scientific paper, the author will give the number he or she has chosen, usually 20 or 25 years.

Regards,
Jim

[K. Campbell]

Years per generation

In my opinion, 25 yrs per gen is used for convenience. Most actual calculations on generation length come up with 33 or 34 years for an average.

30 is a safe, defensible estimate.

[Tassie]

One factor you haven't included in your generation times is the fact that it is only in the last two hundred years that people lived beyond a certain age, were educated or had to delay entering adult society. We are all probably the products of many generations of matings between teenagers or very young adults.

[vinnie]

One factor you haven't included in your generation times is the fact that it is only in the last two hundred years that people lived beyond a certain age, were educated or had to delay entering adult society. We are all probably the products of many generations of matings between teenagers or very young adults.

Or between older men and (much) younger women because in many societies men had to prove they could provide for families before they were allowed to marry. Not to mention that many societies allow(ed) polygamy. So there could have been longer generations between fathers and children than between mothers and children in a lot of places.

Because all of this is still so new, when I do a tmrca calculation I take a conservative approach and use 95% confidence and do both 25 yr and 30 yr generations to give me a general range. I think this has worked well for me, because the tmrca results for my closest ydna match gave me a time frame that coincided with known historical events, strengthening my interpretation of my dna results.

Vinnie

[lgmayka]

One factor you haven't included in your generation times is the fact that it is only in the last two hundred years that people lived beyond a certain age, were educated or had to delay entering adult society. We are all probably the products of many generations of matings between teenagers or very young adults.

Patrilineal generation calculations should be based on the average age of a father at the birth of an average son who himself survives to reproductive age. It is true that centuries ago, people married earlier; but so many children died young that married couples often needed to continue having children well into their 30s (or beyond, for men) in order to ensure that at least one child survived to take care of them in their old age. Moreover, so many spouses died young that widows and widowers were continually remarrying.

A fairly recent example is that of poverty-stricken southern Poland in the late 1800s. A large percentage of those who survived to the age of 35 were widows and widowers who either (a) had no living children and had to frantically seek to conceive at least one surviving child, or (b) had living children and had to frantically seek a breadwinner or homemaker for those children to give them better odds of survival.

The bottom line is that actual genealogies suggest roughly a 30-year average patrilineal generation interval.

[cacio]

lgmayka and vinnie:

very good point about fathers. Those who survived and were rich enough could go on having children until a later age. I did a quick calculation on my own paternal lineage. If I have the right data, I think there were 16 people starting from about 1500 to now, which means an average of 30 years per generation, if not more.

cacio