Reproductive science has come a long way in recent years, but there's still plenty we don't understand - particularly around male fertility. The reliability and availability of data in this field has become more of a concern in light of a study published this year, suggesting that sperm counts worldwide have dropped 62% in the past 50 years. As yet there is no clear answer as to why that is. Professor Chris Barratt is one of the scientists working to change that. He's the Head of Reproductive Medicine at Ninewells Hospital and the University of Dundee Medical School, and has dedicated his career to better understanding male infertility; driving breakthroughs in how to study sperm dysfunctions – and most recently spearheading advances in developing a male contraceptive pill. Chris talks to Professor Jim Al-Khalili about his academic struggles as a youngster, the lecture that changed his life, his research into 'head-banging sperm' and why he believes a new male contraceptive could be a game-changer. Produced by Lucy Taylor.