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Mag Uidhir 6
05-05-2016, 04:26 PM
The take away cut is simply, it appears that 28 yrs per generation is an accurate measure for us within the past 50,000 years.

http://popular-archaeology.com/issue/spring-2016/article/molecular-clock-for-estimating-ages-of-ancient-genomes

client
05-05-2016, 08:02 PM
28 years seems a bit high considering the life expectancies of humans over the years

jdean
05-05-2016, 10:09 PM
28 years seems a bit high considering the life expectancies of humans over the years

It's an average age of prorogation not an average age of life expectancy, people who died young feature less in the former figure but affect the latter.

client
05-06-2016, 03:52 AM
It's an average age of prorogation not an average age of life expectancy, people who died young feature less in the former figure but affect the latter.

People would not be able to have children every 28 years if they weren't able to live for 28 years.
Even if you're saying, many people did live that long, and the life expectancy was brought down by the rest who died earlier, from a survival standpoint, it would be rather stupid to wait for 28 years to have a child in those times.

My estimate would be around 20 years or less.

client
05-06-2016, 03:57 AM
one of my great grandmas apparently got married when she was 5 to my great grandpa who was 10 :lol:

Not sure when they had kids though lol

Saetro
05-06-2016, 08:17 AM
Just remember that this is a long term average. Over that time span.
And one further thing.
STR mutation rates are per generation of 30 years.
You can't use the existing mutation rates and plug in a different generation time.
If you do, you have to change the mutation rates as well and you come up with the same answer.
They are inextricably linked.

lgmayka
05-06-2016, 09:48 AM
People would not be able to have children every 28 years if they weren't able to live for 28 years.
Even if you're saying, many people did live that long, and the life expectancy was brought down by the rest who died earlier, from a survival standpoint, it would be rather stupid to wait for 28 years to have a child in those times.
No offense, but your calculation is "backwards." Here's one simple way to put the question: How old was the father, on the average, when the son was born? Here are some considerations:
- The father had to be of reproductive age.
- Once he had reached that age successfully, he was (on the average) strong/healthy enough to live a couple decades longer.
- He would (on the average) be repeatedly trying to produce sons. He had to reckon with the probability that some would die before they became "useful."
- Arguably, a son born to a 30-year-old father is (on the average) more likely to survive to adulthood than a son born to an 18-year-old father, for both biological and social reasons.

As an example, our family has five sons. The father was 29 at the first son's birth; then 30, 34, 37, and 40. The average (in our family) is a 34-year-old father.

client
05-06-2016, 10:42 AM
But yours is a modern family, with modern amenities, healthcare, good food, clean water etc. We've only been this way for a small fraction of our history, and heck people in underdeveloped countries still don't live this way.

How many people do you think even used to live till the age of 40, 50000 years ago? 10000 years ago? 2000 years ago?

I'm estimating that people would have started having children by 16-18, for much of human history. now to bring the "average age" up to 28, they'd need to continue having children till their late 30s/ early 40s as well.

jdean
05-06-2016, 12:44 PM
But yours is a modern family, with modern amenities, healthcare, good food, clean water etc. We've only been this way for a small fraction of our history, and heck people in underdeveloped countries still don't live this way.

How many people do you think even used to live till the age of 40, 50000 years ago? 10000 years ago? 2000 years ago?

I'm estimating that people would have started having children by 16-18, for much of human history. now to bring the "average age" up to 28, they'd need to continue having children till their late 30s/ early 40s as well.

But that's just your guess, studies of contemporary hunter gathers have concluded they start having children at about the same sort of time as people in more technologically advanced cultures.

The average age per generation on my paternal line going back 12 generations is 35 yrs.

Saetro
05-07-2016, 01:05 AM
My estimate would be around 20 years or less.

An unrealistic figure set as a challenge to generate discussion?

Women can be choosy about partners. They tend to pick someone with a demonstrated ability to support them and children. That can take time, especially after we moved to living in one fixed place about 10,000 or so years ago. It took time to accumulate a little wealth to be attractive.
In some recent hunter-gatherer societies, the older men had precedence in choice of a mate - younger men had to wait.
And then there is the female side. The age of menarche depends on diet, and is lower in modern society, so in general women were not able to start having children as early as would be necessary to average 20 years for the birth of their children. A big study in a western society using extensive birth data over the late C19 found peak female fertility at the age of 24. And a higher incidence of mortality for baby and mother for very young mothers: their bodies were not as strong in their teens.

We do know that men tend to be a little older and women a little younger in partnerships, so quite often in an extensive pedigree, the all mtDNA line tends to squeeze in an extra generation compared with the all Y-DNA line. This study doesn't help with that, even though it is only relevant to a small proportion of all our lines.

jdean
05-07-2016, 09:15 AM
An unrealistic figure set as a challenge to generate discussion?

Women can be choosy about partners. They tend to pick someone with a demonstrated ability to support them and children. That can take time, especially after we moved to living in one fixed place about 10,000 or so years ago. It took time to accumulate a little wealth to be attractive.
In some recent hunter-gatherer societies, the older men had precedence in choice of a mate - younger men had to wait.
And then there is the female side. The age of menarche depends on diet, and is lower in modern society, so in general women were not able to start having children as early as would be necessary to average 20 years for the birth of their children. A big study in a western society using extensive birth data over the late C19 found peak female fertility at the age of 24. And a higher incidence of mortality for baby and mother for very young mothers: their bodies were not as strong in their teens.

We do know that men tend to be a little older and women a little younger in partnerships, so quite often in an extensive pedigree, the all mtDNA line tends to squeeze in an extra generation compared with the all Y-DNA line. This study doesn't help with that, even though it is only relevant to a small proportion of all our lines.

I can only go back 6 generations on my MtDNA line (birth certificates run out at that point and I'm stuck in a small Welsh town where everybody had the same name : ) but it demonstrates your point. at this level the average generation length is 29 yrs but 34 for my paternal line.

By the time my 4x Mtdna great grandmother was born my 4x Y-DNA great grandfather had already had 4 children.

One issue that affects this is men can go on having children for longer than women and are more likely to find new partners after the death of a spouse.

vettor
05-07-2016, 07:28 PM
Just remember that this is a long term average. Over that time span.
And one further thing.
STR mutation rates are per generation of 30 years.
You can't use the existing mutation rates and plug in a different generation time.
If you do, you have to change the mutation rates as well and you come up with the same answer.
They are inextricably linked.

but surely STR mutation rate of 30 years is far to small to use for STR step difference between people ..............I have a figure of 131 years for that

Saetro
05-08-2016, 01:42 AM
but surely STR mutation rate of 30 years is far to small to use for STR step difference between people ..............I have a figure of 131 years for that
It's the generation that is 30 years.

Let me clarify that with an example.
In McDonald's Y STR TMRCA calculator http://clan-donald-usa.org/index.php/tmrca-calculator the mutation rate for 111 markers is given as 0.0026.
This is set for a generation length of 30 years.

So, once the calculator estimates a number of generations, this can be multiplied by 30 to get the estimated time.

ArmandoR1b
05-08-2016, 03:39 AM
........) but it demonstrates your point. at this level the average generation length is 29 yrs but 34 for my paternal line.

.......

One issue that affects this is men can go on having children for longer than women and are more likely to find new partners after the death of a spouse.
But it would be extremely unusual for every generation in the past 10 generations, and even more so over hundreds or thousands of generations, for every generation the father to have been 45 or 50 years old. Over time the average smooths out especially when multiple studies are used. At one time I had put all of the studies together at http://www.isogg.org/wiki/Generation_length#Studies_of_average_generation_le ngth and got 32.5 years per generation.

jdean
05-08-2016, 09:08 AM
But it would be extremely unusual for every generation in the past 10 generations, and even more so over hundreds or thousands of generations, for every generation the father to have been 45 or 50 years old. Over time the average smooths out especially when multiple studies are used. At one time I had put all of the studies together at http://www.isogg.org/wiki/Generation_length#Studies_of_average_generation_le ngth and got 32.5 years per generation.

Exactly, everybody's line is a mixture of eldest, youngest and everything in-between. I use 3 generations per 100 yrs for convenience.