Reports of falling sperm counts and testosterone levels have fuelled fears over chemicals, pollution and modern lifestyles. But how much do scientists agree on what is affecting male fertility? The world is unwittingly walking into a male reproductive crisis, scientists warned this week as they presented data that revealed an apparent halving of average male testosterone levels over the past 50 years. “It is mind-blowing that testosterone has declined by 50%,” Prof Hagai Levine, who led the work