Counting the ancestors

 

Madam, – Congratulations on your excellent “Ancestors” supplement. But I have a problem. When we were celebrating the year 2000, I tried to explain to my grandchildren the process of person to parents to grandparents to greatgrandparents in numbers 2, 4, 8, 16, etc.

One of the bright sparks asked me, how many individual ancestors would he have for the year 1000. Feeling very full of myself and noting that I could introduce a little maths into the discussion, I explained the concept of 2 squared, 2 cubed, etc, and 2 to the power of the number of generations. Taking a generation at 30 years, 2 to the power of 30 for 1000 years ago. Hey presto.

However the same bright spark grabbed his calculator and found that he would need 1.1 million ancestors living in the year 1000 to beget him. As far as I knew the population of Ireland in the year 1000 was around 300,000. He asked me where did the other 700,000 ancestors come from. I was flummoxed

Since then, I have reasoned that an individual could marry twice, and the numbers of required ancestors could be fewer. But I am still wondering. Brian Boru must have been one of the million ancestors. Ryan Tubridy does not have a unique claim! Could a genealogist please help? I must be missing something. – Yours, etc,

Prof NOEL MULCAHY,

Lochlua,

Ballina/Killaloe, Co Clare.