For all McCain clan members, here is a link to a very useful TMRCA (time to most recent common ancestor) calculator. It is calibrated a .002, which should be adjusted for our family. Using subgroups in our family the actual mutation rate is closer to .004, or even .005. To be conservative I use the .004. With this tool you can get an estimate of when your particular branch of the clan ties into the others. Generally, at the .004 setting the generation next to the 60% probability is correct, give or take a generation. We know this using those subgroups that have very good paper records and go back some seven or eight generations. We ran the calculation for them knowing the actual generation back, so it was how we arrived at the .004 mutation rate.
As you use the calculator, you will see we all seem to come from one McCain family circa mid 1600s. It is very possible we all descend from James McKeen or his father. James had two wives in his life (not at the same time fortunately) and the best estimate is 22 children. Some of these are accounted for, but most are not. James McKeen (his and his brother's descendants) are a DNA match to the Port Hall and St Johnston McKeans. We can follow them from 1630 onward. This is the line that has the often mentioned in lore William McKean the soldier.
Anyroad, enjoy: TMRCA Calculator
Comments and feedback welcomed.