There are four primary reasons for multiple births. "It runs in the family" (inherited on the mother's side) and a higher propensity within some ethnic groups; Nigeria has the highest multiple births rates in the world, for example, with Japan among the lowest. However, neither of these are increasing the overall number of multiple births.
The world is ageing rapidly. As fertility falls and life expectancy grows, the num-ber of older people in both the developed and developing world is soaring. By 2050, there will be more than 2 billion people aged over 60 on this planet, out-numbering children below the age of 15 and accounting for 21.5% of the global population.
Together with migration, urbanisation, climate change and population growth, ageing is a transformative phenomenon affecting our world. One of the effects of rapid population ageing across the world is that we are entering the era of the 'age bulge', when the older population increases in size relative to younger people.