Since John “Bane” Mackay dropped the Mackay surname in the mid 15th century, there have been over 20 generations of Bane/Bayne/Bain descendants.
If you think that each generation would have many siblings, it would not take long before the number of descendants reached into the millions.
For example, if there were 4 brothers in the first generation and they each had 4 sons the next generation would have 16, and if each of them had 4 sons the following generation 64 then 256 and so on.
The same principal works on our ancestors i.e. we have 1 set of parents, 2 sets of grandparents, 4 sets of great-grandparents, 8 sets of great-great grandparents and so on.
It would not take many generations back before we get to the amount of possible ancestors being greater than the population at the time, so what causes this and how do we work our how many of us there really is?
The basic answer is down to inter family (cousin) marriages whereby they may have the same grandparents, great-grandparents or possibly even common ancestors further back. Each common ancestor reduces the amount of shared ancestors hence reduces the total amount of possible ancestors.
We can see this happening on most of the trees, whereby second cousins married, or people with the same name who may have shared a common ancestor further back married.
If we assume that there are 20 generations of Bain families and there were 4 children in each generation by the 10th generation there would be over one million, so by the 20th generation this could have been expected to rise exponentially, however the principal above and cousin marriages along with the reduced family size in the latter period of time would have reduced this number substantially.
The following posts are good at explaining the process in a little more depth for those of you that would like more detail.
This is not an area of speciality, just one of those curious quirks I noticed during research, but it does means I still do not have a way of estimating the amount of us Bain’s, therefore if anyone has any ideas or knows the figure, please share.