Last modified on Wed 3 Feb 2021 07.33 EST How does a single fertilised egg divide and morph into an embryo with head, tail, limbs and organs? That question was an inexhaustible source of fascination to the biologist Lewis Wolpert, who has died aged 91. With a twinkle in his eye, he told audiences it was not birth, marriage or death, but gastrulation – the stage in which a uniform ball of cells folds to become differentiated layers with the beginnings of a gut – that was “truly the most important time in your life”. Wolpert combined his interest in fundamental problems of development with a parallel career as a science communicator. He enjoyed performing in public, and brooked no compromise in his quest to persuade people that “science is the best way to understand the world”. He broadcast frequently on BBC radio and TV, and wrote a number of popular books. The best known of these, Malignant Sadness (1999), was a fiercely objective attempt to understand his own experience of a severe depression that he suffered at the age of 65. He gave the Royal Institution Christmas lectures in 1986, chaired the Committee on the Public Understanding of Science from 1994 until 1998, and won the Royal Society’s Michael Faraday prize (for science communication) in 2000.