Final answer:
The hidden momentum of population growth is caused by population age structure, which occurs due to the demographic transition, where a society progresses from high to low birth and death rates. The delayed decline in birth rates after a drop in death rates leads to continued population growth due to a large number of youths. The demographic transition model explains this phenomenon, with economic development playing a significant role.
Step-by-step explanation:
The hidden momentum of population growth is primarily caused by population age structure. This concept, known as demographic momentum, refers to the tendency of a population to continue growing after a fertility decline due to a disproportionately young age distribution. In essence, even when fewer children are being born, the large number of young people reaching reproductive age can still lead to a growing population.
To understand this phenomenon, it is essential to look at the demographic transition model which details the shift from high birth and death rates to low birth and death rates as a society progresses economically and socially. During the early stages of this transition, death rates fell due to improvements in healthcare and living conditions. However, birth rates initially remain high, leading to a surge in population. It is only later that birth rates begin to fall, often as a response to higher standards of living and increased educational and employment opportunities, particularly for women. This lag between falling death rates and falling birth rates creates a period where the population growth rate remains positive and sizable.
The demographic transition highlights the interplay between economic development, birth rates, and population growth. An increase in a nation's income can lead to a reduced growth rate as higher incomes often increase the opportunity cost of having children, thereby contributing to a decline in birth rates. Importantly, although these processes can help to stabilize population growth, they often require considerable time and investment before they take full effect.