Reincarnation

Some people believe in reincarnation, or the beleif that your soul is reborn into another body upon your death. In your next life, you could be reborn into a higher social standing as a reward for your good deeds, or you could be brought back as a pig as punishment. But if people's souls are constantly being brought back in different guises, how many souls are there out there? If each person has a soul, and is reincarnated the moment their old body dies, then the population should never grow. Every time someone dies, someone else should be born. This obviously isnt the case--After all, our population is steadily increasing.
Why assume that you have to be reborn the moment you die? For that matter, why assume that your past life has to have actually been in the past, or your future life at a later date. Time seems to be a fluid concept, not a linear one. For this reason, it makes sense that a person's next life could be anywhere and anywhen. My current life would be that of a high schooler in 2007. My next life could be that of an 18th-century accountant, and the one before that a doctor from 3994. Time is not an issue.
But if time is not an issue, is it not also possible to be reincarnated when your first life is still in progress? To me, it seems possible. I could be living out my 2007 high schooler life right now, and cooexisting with myself 534 incarnations down the road, when I am reborn as one of my classmates. If you look at it this way, its possible for every person who ever lived to be an incarnation of the same being. Beats being reborn as a mosquito.