Today, we learned population pyramid which can reveal a lot of information. If the population pyramid of a country really looks like a pyramid, that means the country has high-percent people who are young, just like lots of African countries. So population of those countries will grow fast and never decrease. Compare with those countries, Russia has lower-percent pre-reproduction people whose age is 0-14, higher-percent reproduction people and old age people. So the population pyramid of Russia looks more like a rectangular. That's the main difference between advanced country and developing country.

We can know birth rate, death rate and actual population of a country from pyramid. There are certain ways that can influence population pyramid, like industrialization, natural disaster and educated woman. Industrialization can provide people with good living condition, medical care and long expectancy. Educated woman results that woman will spend more energy on working instead of boring kids. That's why population pyramid of advanced country looks more like a rectangular.