Jim Wilson, of Dunedin, asks :-

I have a dilemma involving population growth.

As I trace my family tree I was aware that my ancestors doubled with every generation (two parents, four grandparents etc) I then came to the realisation that the number of ancestors would become a very large number relatively quickly. If I assume that each woman had a child when they were 20 years old. then, working backwards, the number of my ancestors far exceeds the "official" world population of about 200,000 in the year 7BC.

While I can understand that disease, war, famine and natural disaster must have accounted for many, I can not understand the significant difference between the two figures, can you help?

Ian Pool, a demographer at the University of Waikato and one of the authors of the book "The New Zealand Family From 1840", responded.

By definition, large families of the past have more descendants than small families; no one is descended from a family with no children. That is why we can all say honestly that our ancestral families were large, they were a biassed sample of all families of the past. They miss all the ones with "spinster aunts", where mothers died young at low parity, or where, like poor Queen Anne, they lost most or all of their children before they had grown to become parents themselves.

Thus, in the 1911 census of Pakeha New Zealand, by which time Pakeha mortality (especially child mortality) was the lowest anywhere, the modal family was one that had few or no children, but by contrast most of the children were members of families with 5 or more children, and they were likey to be the parents of future generations.

If we take Maori of the 1890s, 25 per cent of the girls born into Dame Whina Cooper's cohort would have died by age nine months and 50 per cent before their seventh birthday.

Thus genealogy can be both true and misleading, assuming that your research is conclusive. True about your family, as the chances are that you have descended from atypically large ones in the past, in which numerous children have survived to become adults. Misleading because it is not true of the population as a whole.