What is reincarnation?

It is well known scientific fact that over time, the animal population including human population increases. How does a colloquially scientific religion explain reincarnation if populations increases? Don't give copout answers or rhetorical impulses that I have already heard about this question from many people who were sometimes practising buddhists and buddhist monks. This is an important question that needs rational scientific answers and not wishful thinking. EDIT: No thanks for the copouts. And for guy who said something like it will be the dominant theory if not for the monotheistic religions, no thanks for the royal copout. You should learn how to not be hostile towards my questions Messer's Copouts. Don't be angry. Give rational answers and not the ones where I have read more on it to understand. The answer that I have to read on it more is the biggest copout. Every religion uses that to keep its people in abject poverty. Picture of poor tibetan buddhists here.