The candidates were divided into two teams, males versus females.

They usually start life as females but later develop into males.

The most important is that about 60 percent of the genetic male children raised as female have retransitioned into males.

These hatch out into males, a process known as adelpho-parasitism.

Frogs that had been observed to lay eggs were able to change, over a period of months, into complete males.

These then develop into either females or males and mating takes place.

All ballan wrasses are female for their first eight years before a few change into males.

These eggs are in general viable, developing into males.

However, if two fish start to mature into males at the same time one will become the dominant male.

Females transform into males between the ages of 7 and 14.