Gene Surfing

Adventures in Family History

Magic Numbers

Farmer BullshotThere are a certain numbers that are important to all of us – the speed of light, the golden ratio, prime numbers, the Fibonacci sequence and – my favourite – the number 34.

Okay, the number 34 is probably personal to me – it is the average number of years between generations in my family tree and is strangely accurate, although of limited use.

I was surprised by this number – I would have guessed that generations were about 25 to 30 years apart but it seems not to be the case, at least in my tree.

I was aware that in recent generations of the Sidney family the men in the family did not marry until their late 20’s but the average seems to fit over other branches of the family as well.

The longest branch I can trace is through the Codrington family and this, too, gives a similar result.

Generation Gap

A different number would be obtained if all of my family were descended from the first child in each generation – or, indeed, the last – but 34 seems to be an average based on several factors.

Historically most women marry between 18 and 25 and then have a period of between 10 to 20 years having children – it is only relatively recently that medical advances have allowed us to control the size of families, and for us not to need to have so many children as very few die in infancy.

The world average birth [fertility] rate has decreased from about 5 children for each woman to about 2.5 just in the last 50 years and in the U.K. is currently 1.9

Anne Stubbes (1575-1630), the wife of Robert Codrington, had 17 children before her husband became ill and died in 1618.

Joan Tregarthen (1498-1583) had 14 children by her first husband and then another 6 by her second.

It is not just the age of the women that needs to be taken into account – men seem to marry later in life, especially those who were well educated or were apprenticed for a number of years – and these are often the best documented.

Many of the Codrington family trained as lawyers and did not marry until they were about 30 when they had completed both University and their training at one of the Inns of London.

Obviously it was easier for men to make this sort of decision, but well connected or educated women sometimes delayed marriage – perhaps waiting for the right political or social match.

Most branches of my family I can trace back to about the 1600’s – the Sidneys, Radfords and Burnells – but my grandmother Emily is a “gateway ancestor” who opens up a link into the Codrington family and from there, through various marriages, to King John, William the Conqueror and Charlemagne.

Charlemagne is therefore my 34 x great-grandfather and is generation 36 – with parents and grandparents included.

And the generation number for him calculates as 1224 years meaning that, according to the 34 year rule, he should have been living in about 734 – in fact he was born just 8 years later in 742.

William the Conqueror is estimated as generation 28 (1006) and was born 1024.

King JohnKing John (either my 21 or 22 x great-grandfather) calculates exactly in between 1176 and 1142, having been born 1167.

More recently [?] Robert Codrington, born 1574, fits nicely as 9 x great-grandfather (1584) and my earliest direct Sidney ancestor, William Sidney, 4 x great-grandfather is estimated as 1754 – he was born 1750.

Taking these into account the number 34 may need a bit of tweaking but is close enough as a general guideline to the generation gap – at least for my family tree.

It certainly helps when either estimating the birth of an ancestor or checking whether or not some generations are missing from the branch of a tree, or are just incorrect.

Of course there are exceptions in between those that fit neatly and these can be up to 20 years from the calculated value.

Sir John Beaufort born 1373 should be generation 17 (1380) and my 15 x great-grandfather.

But he is actually my 17 x great-grandfather, and therefore generation 19.

The Charlemagne Assumption

charlemagneWhich leads us to another numeric problem and this is the belief that everyone alive now is descended from Charlemagne.

Using binary mathematics, it seems possible – even a certainty.

The logic seems to be that for every generation you have a specific number of ancestors, and at some point the number of ancestors is the same as the population – you are therefore related to everyone that ever lived.

Just like the grains of rice on a chess-board eventually reaching the moon, the number of ancestors doubles with each generation.

The population in 1900 was estimated as 1.6 Billion, so how far back would you need to go back so that the number of ancestors is equal to the world population?

Surprisingly you only have to go back about 1000 years.

In the year 1066 I would have had 268,435,456 ancestors, from my parents down to William the Conqueror, 25 x great-grandfather.

The world population at the time was 295,040,195 so it only took another generation for me to have more ancestors than is mathematically possible, yet alone reasonable.

And if you just use the population of England you only have to go back to about 1200 to run out of potential ancestors.

But what happens after this?

It doesn’t take many more generations to show that you have more ancestors than the number of people who have EVER lived on the planet.

This cannot be correct therefore a new calculation seems necessary – something that takes this into account.

It seems that for every generation there are a number of ancestors that are related through more than one family connection so you can never be related to all of the population, just a certain percentage.

This percentage of the population probably represents the social class that you belong to and this percentage will probably change based on circumstances, such as the plague – as an uneducated guesstimate I would expect any one person to be related to no more than 50% of the population at any point in the past.

The pattern would perhaps be more of a diamond shape than just an infinite triangle, with each family tree having a maximum capacity at some point in the past – and then you just end up with all the branches leading back to a limited number of ancestors.

Scientific research into mitochondrial DNA published in “The Seven Daughters of Eve”, identifies just 7 women from which we are all descended – the lines of all other women having failed to make it to the present day.

This is quite surprising  considering how many there are of us – currently seven Billion.

But it cannot be correct just to assume that everyone alive today is related to William the Conqueror just because the numbers say so – there are other factors to be taken into account.

Social divisions have been around for a long time and although these seems to have relaxed in recent generations, they still exist.

Religious and cultural differences also play a part in ensuring that we are separated into social streams – and have been for thousands of years.

Men and women still tend to marry others within the same social and cultural circles and this leads me to think that there has never been much of a cross-over between widely separated social classes – peasants and royalty are never likely to marry, although there is always the possibility of the higher social groups taking sexual advantage of the lower.

There are plenty of bastards in most royal dynasties.

The fortunes of families can go down as well as up and social boundaries can blur around the edges, but in my experience there is probably less social movement than I was expecting.

Close Relations

There is a belief that members of noble families – and those from Norfolk – often marry their cousins, but this does not seem to be the case.

Yes it does happen – and not specifically in noble families – and where there is a close family relationship this is often recorded as unusual, such as Queen Victoria.

In Kazakhstan you have to prove that you are not related by at least seven generations before you can marry, so you would learn your family pedigree from an early age.


But as I wander through the branches of the my tree the same family names – and sometimes the same person – appears many times.

It seems that I am related to the Plantagenet King John (both as 21st and 22nd great-grandfather) multiple times through several of his children.

Perhaps we all are and I am just lucky enough to be able to identify this fact?

But of course this issue is being addressed by recent DNA testing and results tend to confirm the original mathematical research done by Joseph Chang in 1999.

The most recent common ancestor of every European today (except for recent immigrants to the Continent) was someone who lived in Europe in the surprisingly recent past—only about 600 years ago. In other words, all Europeans alive today have among their ancestors the same man or woman who lived around 1400. Before that date, according to Chang’s model, the number of ancestors common to all Europeans today increased, until, about a thousand years ago, a peculiar situation prevailed: 20 percent of the adult Europeans alive in 1000 would turn out to be the ancestors of no one living today (that is, they had no children or all their descendants eventually died childless); each of the remaining 80 percent would turn out to be a direct ancestor of every European living today.

I still think there is some way to go with DNA based genealogy, but eventually we will all be able to give a DNA sample and get an accurate family tree going back thousands of years – but where is the fun in that?

Ultimately we all share the same common ancestors if you go back far enough – the challenge for genealogy is identifying where we all belong in this complex pattern.

Chris Sidney 2015





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