Final answer:
Population growth rates are highest when the median age is low and a country is in Stage 2 of the demographic transition, where high birth rates coincide with rapidly declining death rates due to better living conditions and healthcare.
Step-by-step explanation:
Overall population growth rates are most likely to be highest when the median age of a population is low, and a country is in stage 2 of the demographic transition. During the second stage of demographic transition, countries experience high population growth rates because while the birth rate remains high, improvements in medical care and nutrition lower the death rate. This results in a burgeoning population due to a wider base of younger individuals and an increase in life expectancy.
Stage 2 of the demographic transition is characterized by a demographic shift where countries move from a pre-industrial to an industrial society. This stage sees a significant reduction in infant mortality and an increase in life expectancy. The surplus of cheap labor often leads to urbanization as people move from rural areas in search of employment in growing cities, contributing to an expansive population pyramid.
As the demographic transition progresses, high birth rates persist, whereas death rates decrease rapidly, leading to a substantial net population growth. Ultimately, countries transition through the stages, with Stage 2 being the most dynamic in terms of population expansion, while subsequent stages see stabilization and eventual decline in growth rates.