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By this time, the MDCs have either advanced to Stage 4 or are still stuck in Stage 3. In the fourth stage of Demographic Transition, birth rates have  basically stopped moving and are close to equaling the death rates. When this happens, it is called Zero Population Growth; there's no growth or decline. Life expectancy is about 82 years.

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Toward the close of Stage 2, most countries experience the

Industrial and Medical Revolution sometime in Stage 3. For  these countries (MDCs), they have falling birth rates while the death  rates remain as they were. For other countries (LDCs), these advances come later. Life expectancy is now at most 78 years.

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So after giving birth a lot and dying quite a bit, things start to change toward Stage 2. Death rates begin to lower as the Agricultural Revolution hits. People stop wandering as nomads and settle as farmers. This provides opportunity for health to improve as well as diet. Farms mean more people are needed to help. That causes birth rates to remain high, leading to slight population growth. Life expectancy was at most 70 years old, a major improvement.

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The world was in Stage 1 for a while and with a few exceptions has since exited that stage. In Stage 1, our birth rates would've been much higher than they are now as well as high death rates. People at this time were still chasing their food and had yet to discover agriculture. The environment ruled their every move. Life expectancy was low; early man had no knowledge if they would be alive the next day. Overall, there's minimal population growth.