My roommate and I were discussing half-lives last night, and this theory was borne from that discussion...
First, a quick was to visualize half-life for those that don't fully understand it...
Imagine a group of 16 kids. These kids have a half life of 70 years. Here is what that means: In 70 years, 8 of those kids, at random, will be dead. Now, you have 8, 70 year olds. In 70 years, 4, at random, will be dead, leaving you with 4, 140 year olds. After another 70 years, you will have two more deaths on your hands, but you will also have two 210 year olds sticking around. Another 70 years pass, you have one death, and remaining is a 280 year. If you introduce another 15 people and wait 70 years, when 1/2 the group has died, the chance that the now 350 year old is still around is just as likely as everyone else still being around.
Now, imagine Jacob has a half-life. Jacob keeps bringing people to the Island, but he is the only one that remains. The candidates are people that contain elements that represent him. Perhaps Jacob IS 108, and 4, 8, 15, 16, 23 and 42 is best permutation to total the 108 to replace him. Once that group was aligned, he was able to decay, as it were, and move on. The list of names, numbers, etc. are all people that need to come, as a group, to replace Jacob. Only when the proper combination is achieved properly can the sample group decay. Jacob finally found the right mix, and he was able to die.
The MIB and Jacob, in this case, would need to be unique and distinct from one another, otherwise, one or the other would have 'decayed' already in the presence of one another.
There have been episodes entitled The Constant, The Substitute,
and The Variable, which all relate to an equation. Is it too far fetched to think that these weren't also hints? Perhaps Dharma did what Jacob had been trying to do so long when they solved the Valenzetti Equation...