Recent research has suggested a global reproductive crisis could be in the offing, with researchers in Israel saying average sperm counts may have more than halved in the past 40 years. But a study published last month appears to call this narrative into question. Ian Sample is joined by the Guardian’s science correspondent Nicola Davis to unpick why these studies have come to different conclusions – and what could be causing the crisis, if declines are as dramatic as they appear. Help support our independent journalism at theguardian.com/sciencepod