The model approximates what happened to birth and death rates in England and Wales, and to some extent the demographic experience of most developed nations. In stage one both birth and death rates are high and there is relatively little natural increase. In the second stage death rates drop but birth rates remain relatively high, and there is an increase in the rate of natural increase from one year to the next. Total population soars. In stage three death rates level off and it is birth rates that decline.
Natural increase slows, though population continues to grow.
In stage four, which is where many of the world's more developed countries find themselves today, both birth and death rates are low. There is little natural increase, and total population grows slowly if at all.