In the early 1990s it became apparent that hormone-related effects explained some of the strange phenomena being observed in both wildlife (e.g. decreased length of alligators’ penises) and humans (e.g. decreased sperm count). The hormones concerned were not natural, but instead were oestrogen (female sex hormone) mimic pollutants and food components. How do these pollutants, such as the polycarbonate plastic monomer, bisphenol-A, and natural food components such as genistein from soy, switch on the oestrogen receptor and result in biochemical feminisation? What does this mean for fertility in New Zealand and elsewhere? What motivates someone to measure the length of an alligator’s penis anyway? Ian will discuss studies in humans and animals, and will wander off into the world of computer-aided modelling of the oestrogen receptor which reveals all!