Look at it this way.
If generation 1 has eight children and each succeeding generation has 8
children, then by generation 3 you have 512 people. In three generations
you have an increase of 6400%. If your generations start early, say
around 16-18 years of age, you could have 5 generations in 100 years,
and now you're talking 32,678 people >from one original pair of two
people after 100 years. Let's say only half of these people managed to
reproduce at these rates, you're still looking at about 16,300 people
from two original ancestors. So it does not take long for populations togrow geometrically even when a significant proportion of offspring did
not reproduce at the rates shown above.
I hope this helps your understanding of the population growth in that area.
From: "David Goldman" <firstname.lastname@example.org>
I haven't well understood how the Jewish population seemingly grew so much into the
19th century in places such as Podolia where they were about 10% of the population
at the beginning of the 19th century in the wake of the effects of the Khmelnitsky
uprisings and massacres in the 1640s.