The Californian team noticed that a particular type of this receptor appeared to be highly active during pregnancy and the period after birth in mice.

BBC: Chemical clue to baby blues found

While some would prefer to leave things in the hands of their carers, many more would prefer to play an active role in making decisions about the birth.

BBC: Antenatal advice 'perpetuates C-section myths'

In America, as in most rich countries, longer life expectancies and lower birth rates will leave relatively fewer active workers to support the growing number of pensioners.

ECONOMIST: The perils of privatisation