The 21-year-old American son of two lesbians has written a book about his parents’ relationship and the life lessons they have taught him.

Zach Wahls, an environmental engineering student from Iowa City, Iowa, was conceived using IVF and donor sperm in 1991.

A younger sister followed and they grew up raised by their two moms, biological mother Terry Wahls, known as ‘tall mom’, and non-biological mom Jackie Reger, who Wahls calls ‘short mom’.