A soul is never born, so it never dies…But population??

An unsolved question in my mind… If a soul is never born, so it never dies… then why the population increases gradually??? Actually in Holy book “Bhagwat Gita” it is mentioned…The translated version is like this “The soul is never born, so it never dies… It has neither past nor future… It is unborn, ever existing, permanent and ancient… Just as a man discards worn out clothes and puts on new clothes, the soul discards worn out bodies and wears new ones… It is a fact that which is born is certain to die and that the one which has died is bound to take birth… There is no need to worry for the unavoidable…” Whenever I thought about this concept… the only question comes in my mind is --If the soul only transfers from one body to another… then the total number of souls in the earth should be a constant factor… and if one soul belongs to one human beings… then the population should not increase… but it’s opposite… The population is growing rapidly? I discussed this thing with one of my friend… He said that- but the numbers of animals are decreasing from earth…they have also soul… good point… if you say like, then we have been believed that trees having life… they should have also soul… Small to small living objects having soul… even unicellular organism amoeba should have…Now I don’t have that much statistics to calculate the total number of souls in the earth… So I have to stop here my thought process… If anyone finds this thought an absurd one… forgive me for my limited knowledge and my logical thoughts which have no answers…