His team studied 100 children, from early in the womb to the age of seven, to see how testosterone levels have affected their development. They found that even 24 hours after being born, boys - who have up to ten times as much testosterone as girls - were showing less interest in people and more interest in mechanical objects than females.
At 12 months, babies with higher levels of the hormone in the womb had poor eye contact with their parents.
And at 18 months, children with high pre-natal testosterone could not talk or had a limited vocabulary while other youngsters spoke up to 600 words.