From Aristotle to Darwin and Schrödinger to Marie Curie, understanding life has been a scientific and philosophical goal since humans were first able to conceptualise their subjectivity. Sam McKee argues that there is no point in searching for life in other worlds when we do not know what it is on our own planet. Many a debate today centres around a dispute over the definition of life, whether that be abortion politics, assisted suicide or evolutionary biology. McKee argues that we must focus on the definitional question of life before we look for it elsewhere, and to do so we must ask new questions.

I sat recently with a Mars rover engineer, who was enthusiastically sharing with me the search for life’s signature on the surface of the red planet. As a board member of the Mars Society UK, these engineers and astrobiologists are our eyes and ears. On the drive home, it struck me how difficult we seem to find it today to define life: whether that be in evolutionary biology in a Linnaean manner, in the politics of an abortion debate, or in philosophy in the ongoing disputes over whether we possess free will or moral agency. The new humanist calls for assisted suicide show our struggle over those that are functionally living, yet not maintaining a quality of life as they had previously been. Life is both a present reality and something of a spectrum that is hard to pin down.

SUGGESTED VIEWING The mystery of emergence With Suchitra Sebastian, Hilary Lawson, Philip Goff, Jack Symes