Is it good for there to be both males and females of our species? This question seems highly fanciful, and a long way from the ethical questions that health professionals face on a daily basis. However, philosophical thought experiments like this sometimes help to clarify questions that are of much broader relevance. In this case, the prospect of an all-female planet focuses our attention on what it means to be normal or abnormal, on the nature and implications of the different behaviour of men and women, on the political ramifications and resonances of bioethical debate, and on our obligations to future generations.

The possibility of an all-female world has featured in recent debates about enhancement—the use of medical technologies to enhance the capacities and characteristics of humans beyond what is considered normal. Philosopher Rob Sparrow has provocatively suggested that since females have a longer lifespan and are able to bear children, supporters of enhancement should support the deliberate selection of only female …