How come we can only go back 15 generations on our family list ?

+2 votes
795 views
Was wondering why we can only go back 15 generations on our family list and dynamic tree .
in WikiTree Tech by Barb Howell G2G Rookie (290 points)
recategorized by Ellen Smith
Most PM, I was told last year, don't have more than 10 generations. The number set is arbitrary.  If you add the tags Wikitree Tech, profile improvements, that group of volunteers will examine the idea of increasing the number of generations. The idea that there's about 20 yrs to a generation would indicate 15 generations is about 300 yrs .
300 years and in excess of 32,000 individuals. And what would be the point? any one of them would have so little bearing on heredity as to be meaningless.

Well, yeah, Tom, the DNA peters out, that's true -- the gist of what I read in g2g forum on DNA and heredity and the time frame is that it peters out the further into the past your ancestral line is located ... that the consensus is that even 10 generations is stretching it 

It's not like we run out of DNA, just that the bits that identify us as related "disappears" 

The dynamic tree shouldn't be limited to 15 generations -- do you have an example of that happening?
Interesting Q, Jamie -- how many PM have lines extending back into the past by 15+ generations?

My Smith-Wooten is only 11 generations including myself

2 Answers

+3 votes
 
Best answer
Hopefully a true software engineer will jump in, but here's the thoughts of a dilettante.

I suspect the Wikitree developers were worried that allowing an unlimited number of generations could cause the creation of the lists to consume too much server resources and slow-down response time for other users. For example, when I do a 5 generation Family List, I get a response instantaneously, when I do a 10 generation Family List, it takes about 1.5 seconds; but when I do a 15 generation list, it takes 4.5 seconds. Apparently whatever algorithm is being used seems to result in the time required going up by about the square of the number of additional generations, so a 20 generation list would probably take 13.5 seconds and a 25 generation list over 40 seconds. Besides consuming server-side resources, browsers time out if they don't get a response back from the server within a certain period of time, so if creating the list took more than a minute or 2, you would get an error message instead of a list.

While I think this may have been the concern, I'm not sure how valid it is because most lines dead-end at some point, rather than keep going back indefinitely so I think you start having to search a smaller and smaller number of lines at some point.
by Chase Ashley G2G6 Pilot (209k points)
selected by Susan Smith
Chase, that is an excellent point to consider and I don't doubt it has a role in the cut off being at 15
+2 votes

I'm not going to be tremendously helpful, Barb, but some thoughts do occur spring-boarding off Susan's and Tom's comments. First, I don't know of any uses of 20 years as an average generational interval other than anthropological studies trying to reach as far back as the Neolithic. For genealogical relevance, the average generation length is longer.

For estimates, I typically use 32 years for males and 26 years for females--sex-averaged at 29--based primarily on work by anthropologist Jack Fenner (Jack N. Fenner, "Cross-cultural estimation of the human generation interval for use in genetics-based population divergence studies," American Journal of Physical Anthropology 128 (October 2005): 415-423. https://doi.org/10.1002/ajpa.20188) who found average generation intervals in hunter-gatherer societies of 31.5 years for males and 25.6 years for females; 30.8 and 27.3 years, respectively, in males and females in more developed countries...so still 29 years if sex-averaged. That's in pretty close agreement to other research like Helgason et.al. (American Journal of Genetics, 2003) 31.9/28.7 [male/female values]; Matsumura and Forster (Proceedings of the Royal Society of Biological Sciences, 2008) 32/27; Donn Devine (Ancestry Magazine, 2005) 33/29. Turi King and Mark Jobling (Molecular Biology and Evolution, 2009) settled on 35 years for males of British origin.

Nit-picking, I know. But the difference adds up quickly if working TMRCA for many generations back, and the male/female distinction becomes important when dealing with yDNA. Using Turi King's estimate of 35 years (from the 2009 publication mentioned above and another paper in Current Biology, 2006), a 15-generation TMRCA would be estimated at 525 years before the birth of the current DNA test-taker, so call it about 1445 AD, shortly after the time when surname adoption was becoming common in the British Isles. The sex-averaged 29 year interval at 15 generations would put us at about 1535.

I for one am guilty of frequent use of the term "genealogical timeframe"...something which doesn't have a firmly established definition. Family Tree DNA defines it as, "The genealogical time frame is the most recent one to fifteen generations." Wikipedia approximates it as "c. 1500 onwards." ISOGG has one of the most liberal definitions: "the period in which it is possible to find genealogical records relating to individual ancestors." The BCG has no specific definition. As common usage, though, it is the period in which, for a particular region, surnames were first consistently adopted as an identification of lineage.

The reason is simple: evaluating genealogical information is extraordinarily difficult if there is no consistent naming record from generation to generation. Standardized naming systems are probably oldest in China; in the time of the Shang Dynasty surnames had become patrilineal. Confucious's family tree is supposedly 80 generations in depth. But in the 5th century, the use of family names was unusual in the Eastern Roman Empire, and they weren't used at all in Western Europe when the empire fell. The practice started gaining popularity in the 9th or 10th century around the Caucasus in Eastern Europe, and began to spread west. The first known use of a surname in the British Isles was in Ireland, in 916. It was the Domesday Book in 1086 and the advent of taxation by the Normans that led England to start to see consistent surnames, but it was still rare into the 13th century. It would be another century or two before the practice had gained popular ground in the British Isles, and some Scandinavian countries didn't move away from patronymics until the 18th century. It wasn't until the early 19th century, and a decree by Napoleon, that the then-French-annexed Netherlands had to adopt and register distinct surnames.

So Tom's point that "any [15th generation ancestor] would have so little bearing on heredity as to be meaningless" is well-taken. I'm as much or more geneticist as genealogist, and I admit I blank-out and begin thinking about what bills are due or what to make for dinner when the topic is a family tree that's, say, 25 generations old. In the case of Western European descent it's almost impossible to prove, and it makes so much more sense to me to pay most attention to, as Susan points out, the accuracy and breadth of the most recent 10 or so generations. I don't know why WikiTree decided to make the Family List and Dynamic Tree go only to 15 generations, but since that should put us back about the mid-1500s I think it's a reasonable demarcation point.

As Susan said, though, adding the "improvements" tag to the question would bring it to the attention of the folks who could look at possibly extending the reports beyond 15 generations.

by Edison Williams G2G6 Pilot (273k points)
Another point to consider on the Chart of Descendants / Ancestors and the Family List is that those are displaying only the paper trail. They do not depend on any of the DNA test results that may have been posted. The profiles include the proven as well as the unproven in terms of DNA.

So DNA "peters" out in terms of the bits that identify us as possibly or probably related; the DNA itself does not disappear, if you are born you have DNA. That was also mentioned.

And there's no harm done in asking why is the list limited to 15 generations. It is something I was curious about, but which got buried under other questions I though more important at the time.  

I still think the number 15 is arbitrary, but it's possible that it reflects the situation of so many PM at WT, that so few have located in their paper trail more than 8 or 10 generations ... ALES might be able to say one way or the other (Wikitree Tech)
Also, Edison, the use of "20 years to a generation" is a classic baseline and not to be disdained. If the PM chooses to use some other benchmark, so be it. I use 20 yrs because when I was being taught it was the baseline (something like 50 yrs or so ago? Wow. How time do fly.) and I've had no compelling reason to discard it as a baseline.

I am not ignorant of nor unaware of the fact that "generations" merely refers -- essentially -- to a birth order over a period of time ... I have looked at the Family List sorted by date of birth and it is interesting, sometimes you see a child's uncle born a few years after the child himself (herself) is born .... the question of "How can my uncle be of the previous generation when he was born five years after I was?" intrudes

Also I have noted that the variety of years used by various sites and researchers to define a generation also depends heavily on the population they are studying, and the geographical location and the cultural influences of that location ... and the area in which I have been immersed the cultural / economic age was about 23 to 25 for men, and as young as 14 for women. It is not unusual either for a woman of 18 to be first married to a man as his 2nd or 3rd wife and him a good 20 yrs or more senior to her.  

All these are factors in "what is a generation in terms of years" and as is noted will vary by nation, era, culture and demographics, and opportunities.

"...The area in which I have been immersed the cultural / economic age was about 23 to 25 for men, and as young as 14 for women. It is not unusual either for a woman of 18 to be first married to a man as his 2nd or 3rd wife and him a good 20 yrs or more senior to her."

Absolutely! That's why, unless the actual genealogy is known, we can only look at generational intervals as an average. The actual genealogies can vary from an average by a lot. For example, my father was getting near his 60th birthday celebration when I was born, and his father was born when my great-grandfather was 42. If we look only at that sampling, it would say the average interval between the male generations is 50.5 years! surprise

But the larger the sample size, the more the average interval evens out. I copied some of your own WikiTree info into a database, starting with your great-grandparents (can't use your grandparents because your parents' birth dates aren't visible) going back as far your 6g-grandparents where available. I didn't include Elizabeth Lewis (1754) and her ancestors, or Israel Outhouse and Dicy Fryer because I think there may be some problems with their birth dates, but still had 81 individuals: 37 females and 44 males.

The numbers may surprise you. The average female generational interval is 27.84 years, and the average male's is 32.23. For a sex-averaged value of 30.04 years.

So it's pretty darned close to the 26 years for females, 32 for males, and a sex-averaged 29 years that I noted above.

BTW, I wouldn't be surprised if we find our lines crossing paths sometime. I was particularly intrigued by your Huffman line in Texas. Melissa Olivine was born in Oct 1840 in San Augustine. In 1832 one of my ancestors, William McFarland, was on a committee that selected the site for San Augustine and, being a surveyor, he platted the land. In 1833 he became alcalde, and in 1836 he was appointed chief justice of the newly organized San Augustine County. He died two months before Melissa Olivine was born, but it's entirely possible that he knew her parents. And William's son, Thomas, remained in the area until his death in 1880.

Nothing like being whelmed by numbers and statistics. Thank you for sharing these findings, Edison -- mind you, if I were not speechless because I've been whelmed, I could throw out a bon mot or two ...

Hi, Susan! I assume you'll be notified by email of this follow-up post, so here's the topic you were looking for!

I really wasn't trying to convince you of anything. No sales pitch. laugh I was just curious because of your experience with a 20-year average generational interval so I simply copied into a database the WikiTree info for all of your own ancestors (except for a few; I added a comment to Outhouse-32) back to around 1600-1650; 81 one of them, to be exact. I didn't use all the family members, just your biological ancestors; would have taken a long time otherwise because I'd have had to jump around from profile to profile. I still have those numbers (they're just ancestor's name, birth year, gender, and age of child at birth, plus the totals and averages), if you want a copy.

I think one of the issues may be terminology. Generational interval isn't about the age at which a couple is married; it's each of their ages when a particular child is born. For example, if you take George Pemberton (born 1771) and Sarah Pemberton (born abt. 1765), and consider their two children: Bennett Pemberton was born about 1790, and Stephen Pemberton was born 1798. That means George was about 19 when Bennett was born, and 27 when Stephen was born. Sarah was about 25 for Bennett and 33 for Stephen. That's an instance of 19 and 27 datapoints for males, and 25 and 33 for females. That way-too-small sampling would tell us the average generational interval for males would be 23, for females 29, with a sex-averaged value of 26.

Elizabeth Tinsley was the ancestor of yours who had her first child at age 14...and that youngest, John Chaffin, is included the numbers I ran. But Elizabeth had a lot of kids. WikiTree shows she had her last at age 46. If you average her age at the time of birth of each of her 14 children, you get 31.

Some of what I do involves yDNA only, and trying to estimate the time to most recent common ancestor (TMRCA) can become more important there, and why when I cited the handful of published studies above, I kept the average generational interval distinction between males and females.

For genealogy, in general, having an averaged handle on "how long is a generation" really isn't a big deal. Simply doesn't matter much. But sometimes when you're looking at a bit of DNA evidence, though, and have no known connection to the paper trail, you have to start somewhere, often with nothing more than wild-guesswork hypotheses, and the average generational interval can factor into that.

Whelmed. Again. Okay, I use the baseline 20 yrs for the generational span.  This is based on the first born child and ASSUMES (think that would be the correct word) that the father was was at least 20 and the mother was no younger than 14.  Assumes translates to "supposing this to be the case, but without proofs" and of course proofs will be sought (at least I will seek them; cannot answer for others' actions)

A baseline is often arbitrary (in my experience) because you have to start somewhere and that's as good a place as any to start from -- groom abt 20/25 and bride 14+. It is permissible to use this baseline. It can be altered when proofs are located.

Others who are involved in researching and /or managing various branches (lots and lots of cousins are involved) do this thing with DNA but the DNA doesn't have anything to do with my using my baseline.

And while your study is interesting, it doesn't affect me using my baseline, which is admittedly arbitrary but adjustable to proofs presented.  

LOL Have you looked at the google maps, the ones that show the distance tween say Missoula, MT and San Jose, CA (1011 miles), and noted there's these icons (bus, on foot, passenger vehicle, bicycle) ... well, this situation of this gentle flow of whelm is me on foot and you in a passenger vehicle, eventually we each reach the destination, but by differing means

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