The global human population has been growing exponentially for the last few centuries:
At first glance, the number of people here now (over 7 billion) seems about the same as the number of people who lived throughout history before the 20th century. That wouldn’t seem to leave room for any past lives.
However, past population figures are easily misunderstood. They tell us only how many people were alive at different points in time, not how many different people actually lived (and died) over a period of time.
Fertility and mortality rates affect this number a great deal.
We can calculate the number of lives born over a given period from an estimate of the number of births per head of population per year. Currently that figure is about 20 births per year for every 1,000 people. (And in ancient history it was more like 80.)
So for example, the average population may have been 1.4 billion in the 19th Century, but that doesn’t mean that just 1.4 billion people lived between 1800 and 1899. In fact, almost 6 billion people were born in the 19th century. In the 20th century, there were another 13 billion lives.
According to estimates by the Population Research Bureau, about 60 billion have been born since 1 AD. And stretching back into prehistory, at least another 47 billion were born before that. This adds up to 107 billion. That’s a conservative estimate, but it’s still enough to give each of us alive today at least 14 past lives.
There is another important factor in the relationship between reincarnation and world population.
The number of people living now, or at any other point in history, tells us nothing about the actual number of souls involved, as we don’t know how many are ‘off-world’, between lives. What if, say, there are actually 10 billion souls reincarnating on Earth, but only a percentage of those are ever present on the planet at the same time? (E.g., over 70% at present.)
So it’s not that the number of souls must have increased. Perhaps all that has increased is the proportion of souls being on Earth at the same time.