Science is an accumulative body of knowledge, and what was once an astounding breakthrough quickly becomes background information. Three pages in a standard A-level biology textbook can teach you about the helical structure of DNA, whose discovery won a Nobel Prize for Crick and Watson fifty years ago, while two paragraphs are enough for John Scott Haldane’s century-old work in understanding how we breathe. Yet Haldane deserves to be celebrated not only for his discoveries, but for the manner in which he practised science. Nothing demonstrates his approach better than the way he made the miner’s canary a safety device.

Any tiny creature would have served as well. Investigating mine explosions and sewer poisonings in the late nineteenth century, where carbon monoxide and other lethal gases lurked invisibly in the air, Haldane himself usually carried a mouse. With