Final answer:
To keep a population stable over time, a Total Fertility Rate (TFR) higher than the global 'average' TFR of 2.5 is needed.
Step-by-step explanation:
To keep a population stable over time, the Total Fertility Rate (TFR) needs to be equal to the replacement level, which is slightly greater than two. In this case, the global 'average' TFR is 2.5, which is greater than the replacement level. Therefore, a TFR of more than 2.5 is needed to keep the population stable over time.