I know that Margaret was my 7 x great grandmother on my birth father's tree and that she was the second wife of David Sandeman who married her in 1716 shortly after his first wife died. Their twelve children over the 18 years between 1717 and 1735 were Catherine, Robert, David, John, William, George, Margaret, Jean & Patrick (twins), Janet, John and Thomas. All good, strong British names. Possibly one of them could not only name his or her siblings, but also had details of their children and, even more surprisingly, their children's children, to such an extent that they could count those who were living and those who had died. Wow !
In this day and age we all have lists of ancestors and descendants at out fingertips on our PCs but this was 1778. It was long before the first commercially available typewriter or the first telephone or anything resembling a spreadsheet, so how did this person collect the information and record it ? I don't have the answers other than the obvious that it must have been collected by verbal communication and then hand written in a form which could be updated as more individuals were born and died. Quite a task for anyone. The Sandeman family was certainly one which was reasonably wealthy, probably educated, but even with that background you would need to be a meticulous record keeper with a handle on all the goings on within each branch of the family to record all the births, marriages and deaths. I doff my cap to whoever this person was as they were obviously an early example of what became known as a 'genealogist'.