It’s a boy! No, wait…

Babies born apparently female in Salinas, Dominican Republic, are turning into men at puberty due to a genetic deformity. Above, Catherine and his cousin Carla, who is currently undergoing the transition

This condition of gender transition is so common that the children of Salinas afflicted with it are referred to as Guevedoces, or ‘penis at 12 years’.

Around two per cent – or one in 90 – babies from Salinas, marked above on the map, are thought to be born with the condition, which occurs due to a missing enzyme during pregnancy

This unusual condition was first discovered and described in the 1970s when a scientist from Cornell visited the island.

Babies usually form male sex organs after around eight weeks in the womb, with the change triggered by hormone dihydro-testosterone. A handful of babies, however, do not have the enzyme that triggers the hormone surge and consequently they will not form male genitalia until they reach puberty, when there is another surge of testosterone.

BBC Two’s Countdown to Life – The Extraordinary Making of You explores this remarkable example of human diversity and admits that sometimes even the most complex, crucial to our species processes can occasionally go wrong.