So to recap,  we have these four stages of transition: in the first stage, we have high death rates and high birth rates, and they are matched, so that the population remains stable; in the second stage, the death rate plunges as new technology, uh, improvements in standards of living, increased nutrition, medicine, sanitation, and so on, mean that more children reach adulthood and adults live longer this leads to a big boom in the population because the family sizes stay the same just as many children are born as before; and then there is the stage when the birth rate decreases and it comes down to match the new, low death rate; and finally, in the final stage, stage four, we see a balance between these two, so we have a new higher population because we've gone through this population boom but the population is no longer increasing. 