What are the causes of the exponential growth in population?

Question

What are the causes of the exponential growth in population?

Answer 1

If the fertility rate is greater than   the replacement level each generation increase by a factor g. This means that after n generations the population P=Po(1+g)^n which is exponential growth. However the fertility rate is most countries  is at or below replacement level so the population of world is not experiencing exponential growth and the growth we see is due to longer life expectancies which is not exponential.