For a population to replace itself over the long run, women need to have about 2.1 children on average: slightly more than 2, because a few more boys than girls are born and not every child reaches adulthood. The UN estimates that around two-thirds of humanity already lives in a country where fertility is below that level. The club now includes India, China, Brazil and the United States.
That's the estimate from a WHO-led study published in The Lancet in 2024, covering the half-century since the Expanded Programme on Immunization was launched in 1974. It works out to about six lives saved every minute, mostly infants. The measles vaccine alone accounts for around 60% of those lives.
According to the World Gold Council, about 216,000 tonnes of gold have been mined in all of human history. Because gold is so dense (19.3 tonnes per cubic metre), it would fit in a cube about 22 metres on each side, roughly the height of a seven-storey building. Strikingly, about two-thirds of it has been mined since 1950.