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Flat refusal
The last word– IS ANYBODY THERE? I have two parents, four grandparents, eight great-grandparents, and so on. If I drew a family tree going back 10 generations, I would have to make space for a top line of 1024 ancestors. At 30 generations I would expect to see a line of over a billion ancestors. If I tried to research my family back 40 generations (only about 1000 years) I would be searching for the names of vastly more people than have ever lived. This is impossible, of course, but everyone has two parents, so what exactly is wrong with my reasoning?
The simple answer is that people marry their cousins or half-cousins. If you can have shared ancestors at the close proximity of cousin level, then imagine the number of shared ancestors there would be going back 40 generations. Although the calculation is strictly correct, it makes the mistake of assuming that all the names on that family tree are unique, when in fact there will be individuals that appear many times over. For example, if your parents were cousins you would only have six great-grandparents and not eight; and at the 10th generation point, assuming no other shared lineage, there would be 768 grandparents not 1024. Although people tend not to marry their cousins, you would only ever have to go back a handful of generations to find common ancestors, and the further back you go, the more repetition there would be. Jim Rogers Maidstone, Kent, UK Questions and answers should be kept as concise as possible. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and a fax if you have one. Questions should be restricted to scientific enquiries about everyday phenomena. The writers of all answers that are published will receive a cheque for £25 (or the US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted
Instead of starting in the present day and working back, start back in time and work forward. Two young couples are marooned on an uninhabited desert island. With plenty of food and not much to do, they have 10 children each – equal numbers of boys and girls – who later pair up and have 10 children each. The island population is now 124, made up of 100 children, 20 parents and 4 grandparents; and not as the questioner suggested, 200 parents and 400 grandparents. The reasoning is valid only if no one is related. But, as on the island, vast numbers of us share common ancestors. In fact, because the questioner has a British-sounding name, he is possibly a distant cousin of mine… Gordon Black Hamilton, South Lanarkshire, UK One way to resolve this problem is to examine a detailed family tree. A good example is that of the UK’s Prince Charles, as given in The Lineage and Ancestry of HRH Prince Charles, Prince of Wales by Gerald Paget (published by Charles Skilton, 1977). His parents are third cousins because each has Queen Victoria and Prince Albert as two of their 16 greatgreat-grandparents. This means that Charles has 30 and not 32 different great-great-great grandparents. It gets more complicated. Two of the great-great-grandparents of Queen Elizabeth (Charles’s mother) are also Prince Philip’s great-grandparents so the number of Charles’s forebears is further reduced. Paget attempted to identify all 262,142 individuals who comprise 17 generations of Charles’s family. by readers in any medium or format. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK (fax +44 (0) 20 7611 1280) or by email to [email protected] (all correspondents should include their postal address in order to receive payment for answers). If you would like a complete list of all unanswered questions please send an SAE to LWQlist at the above address.
Memorable answer? The Last Word and New Scientist have teamed up with Crucial Technology (www.crucial.com/uk) and will be awarding each successful author a 512MB Gizmo! overdrive.
070127_R_Lastword.indd 149
Last Words past and present, plus a full list of unanswered questions, are available on New Scientist’s website at www.newscientist.com
He succeeded with all but 83,800. Of those he did identify he discovered not 178,342 individuals, but just 11,306. The difference (167,036) was due to duplication by intermarriage. So the number of ancestors is only 6 per cent of what might have been expected. This proportionate reduction increases the further back you look. Go back far enough and we are all twigs at the bottom of the same tree. J. R. Johnstone Nedlands, Western Australia
“If your parents are first cousins this immediately duplicates a quarter of your ancestral tree” People marry people they know from similar geographical, religious or social backgrounds – so marrying cousins is common. If your parents are first cousins this instantly duplicates a quarter of your ancestral tree. Allowance must also be made because the length of a generation is variable. Oldest sons of oldest sons breed faster than youngest sons of youngest sons because they can pack more generations into a century. Add to this cases where someone has an elderly father and a teenage mother and the generations rapidly get hopelessly mixed. The same person could be your grandfather on one branch of the family tree, and your great-great-grandfather on another. If you tried to trace every branch back a dozen generations you would actually end up with a complex network. The smaller the population of target ancestors the more convoluted it becomes. While most people in the past stayed in one place,
a small percentage such as soldiers, sailors and members of parliament were mobile, ensuring cross-breeding nationwide over a period of centuries. It is more revealing to calculate the probability of a given person who was living hundreds of years ago being your ancestor. When writing for the Society of Genealogists, I built a computer model to give approximate figures for dates in the past. In England the population fell to its lowest level for centuries at the time of the Black Death in 1348-49. My model revealed that if you have English blood in your veins, the chances are high that any named survivor of the plague is your ancestor (assuming they had children). Go back to 1066 and the model shows that everyone then living in England who had descendants is your ancestor and mine – and every other descendant (including the majority of readers of New Scientist worldwide) is our cousin. Something similar no doubt goes for all Europeans whose ancestry dates back to the time of Charlemagne (AD 742 - 814). Further back, the Roman armies in England included many from the Middle East and Africa, ensuring an even wider spread of ancestors. Chris Reynolds Tring, Hertfordshire, UK
THIS WEEK’S QUESTION Flat refusal Why are fizzy drinks such as lemonade, cola or champagne far more appealing than the same liquid once it has gone flat? Olaf Lipinski Bad Homburg, Germany
WHY DON’T PENGUINS’ FEET FREEZE? The latest collection from The Last Word, answering some of the world’s most baffling questions Available in bookstores and online at www.newscientist.com/lastword3.ns
17/1/07 3:48:20 pm
The simple answer is that people marry their cousins or half-cousins. If you can have shared ancestors at the close proximity of cousin level, then imagine the number of shared ancestors there would be going back 40 generations. Although the calculation is strictly correct, it makes the mistake of assuming that all the names on that family tree are unique, when in fact there will be individuals that appear many times over. For example, if your parents were cousins you would only have six great-grandparents and not eight; and at the 10th generation point, assuming no other shared lineage, there would be 768 grandparents not 1024. Although people tend not to marry their cousins, you would only ever have to go back a handful of generations to find common ancestors, and the further back you go, the more repetition there would be. Jim Rogers Maidstone, Kent, UK Questions and answers should be kept as concise as possible. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and a fax if you have one. Questions should be restricted to scientific enquiries about everyday phenomena. The writers of all answers that are published will receive a cheque for £25 (or the US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted
Instead of starting in the present day and working back, start back in time and work forward. Two young couples are marooned on an uninhabited desert island. With plenty of food and not much to do, they have 10 children each – equal numbers of boys and girls – who later pair up and have 10 children each. The island population is now 124, made up of 100 children, 20 parents and 4 grandparents; and not as the questioner suggested, 200 parents and 400 grandparents. The reasoning is valid only if no one is related. But, as on the island, vast numbers of us share common ancestors. In fact, because the questioner has a British-sounding name, he is possibly a distant cousin of mine… Gordon Black Hamilton, South Lanarkshire, UK One way to resolve this problem is to examine a detailed family tree. A good example is that of the UK’s Prince Charles, as given in The Lineage and Ancestry of HRH Prince Charles, Prince of Wales by Gerald Paget (published by Charles Skilton, 1977). His parents are third cousins because each has Queen Victoria and Prince Albert as two of their 16 greatgreat-grandparents. This means that Charles has 30 and not 32 different great-great-great grandparents. It gets more complicated. Two of the great-great-grandparents of Queen Elizabeth (Charles’s mother) are also Prince Philip’s great-grandparents so the number of Charles’s forebears is further reduced. Paget attempted to identify all 262,142 individuals who comprise 17 generations of Charles’s family. by readers in any medium or format. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK (fax +44 (0) 20 7611 1280) or by email to [email protected] (all correspondents should include their postal address in order to receive payment for answers). If you would like a complete list of all unanswered questions please send an SAE to LWQlist at the above address.
Memorable answer? The Last Word and New Scientist have teamed up with Crucial Technology (www.crucial.com/uk) and will be awarding each successful author a 512MB Gizmo! overdrive.
070127_R_Lastword.indd 149
Last Words past and present, plus a full list of unanswered questions, are available on New Scientist’s website at www.newscientist.com
He succeeded with all but 83,800. Of those he did identify he discovered not 178,342 individuals, but just 11,306. The difference (167,036) was due to duplication by intermarriage. So the number of ancestors is only 6 per cent of what might have been expected. This proportionate reduction increases the further back you look. Go back far enough and we are all twigs at the bottom of the same tree. J. R. Johnstone Nedlands, Western Australia
“If your parents are first cousins this immediately duplicates a quarter of your ancestral tree” People marry people they know from similar geographical, religious or social backgrounds – so marrying cousins is common. If your parents are first cousins this instantly duplicates a quarter of your ancestral tree. Allowance must also be made because the length of a generation is variable. Oldest sons of oldest sons breed faster than youngest sons of youngest sons because they can pack more generations into a century. Add to this cases where someone has an elderly father and a teenage mother and the generations rapidly get hopelessly mixed. The same person could be your grandfather on one branch of the family tree, and your great-great-grandfather on another. If you tried to trace every branch back a dozen generations you would actually end up with a complex network. The smaller the population of target ancestors the more convoluted it becomes. While most people in the past stayed in one place,
a small percentage such as soldiers, sailors and members of parliament were mobile, ensuring cross-breeding nationwide over a period of centuries. It is more revealing to calculate the probability of a given person who was living hundreds of years ago being your ancestor. When writing for the Society of Genealogists, I built a computer model to give approximate figures for dates in the past. In England the population fell to its lowest level for centuries at the time of the Black Death in 1348-49. My model revealed that if you have English blood in your veins, the chances are high that any named survivor of the plague is your ancestor (assuming they had children). Go back to 1066 and the model shows that everyone then living in England who had descendants is your ancestor and mine – and every other descendant (including the majority of readers of New Scientist worldwide) is our cousin. Something similar no doubt goes for all Europeans whose ancestry dates back to the time of Charlemagne (AD 742 - 814). Further back, the Roman armies in England included many from the Middle East and Africa, ensuring an even wider spread of ancestors. Chris Reynolds Tring, Hertfordshire, UK
THIS WEEK’S QUESTION Flat refusal Why are fizzy drinks such as lemonade, cola or champagne far more appealing than the same liquid once it has gone flat? Olaf Lipinski Bad Homburg, Germany
WHY DON’T PENGUINS’ FEET FREEZE? The latest collection from The Last Word, answering some of the world’s most baffling questions Available in bookstores and online at www.newscientist.com/lastword3.ns
17/1/07 3:48:20 pm