Around the world, fertility rates are dropping. The rate for each generation to replace itself is an average of 2.1 births per woman - and many countries are well below that figure. Does it matter? Surely reducing the population will make the Earth's resources go further? In this edition of Weekend One on One we hear from Associate Professor Michael Giarrusso from the University of Texas, who says unless this trend is reversed, the world’s population will peak in the next 40 to 60 years and then plummet, causing major global issues.