In 1950, the global fertility rate was an average of 4.7 children, but today that has dropped to 2.4.
This is due to increased access to contraception and that women are opting to pursue careers and tackle the subsequent debt from school before considering children.
World events such as the 2008 recession also played a role in hampering population growth.
US-based research group, the Brookings Institution, predicts there could be 500 000 fewer babies born in 2021 due to the pandemic.
According to the University of Washington's Institute for Health Metrics and Evaluation, 23 countries, including Japan and Spain, are expected to see their populations halve by 2100.
In an inverted age structure where the old outnumber the young, there are concerns about who will take care of seniors.
This can also have a detrimental effect on a country's workforce and productivity.
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