From a single cell--a fertilized egg--comes an elephant, a fly, or a human. How does this astonishing feat happen? How does the egg "know" what to become? How does it divide into the different cells, the separate tissues, the brain, the fingernail--every tiniest detail of the growing fetus? In this Very Short Introduction, renowned scientist Lewis Wolpert shows how the field of developmental biology seeks to answer these profound questions. A distinguished developmental biologist himself, Wolpert offers a concise and highly readable account of what we now know about development, discussing the first vital steps of growth, the patterning created by Hox genes and the development of form, embryonic stem cells, the timing of gene expression and its management, chemical signaling, and growth. Drawing on scientific breakthroughs in genetics, evolution, and molecular biology, he illuminates processes that are deeply rooted in evolutionary history, revealing how information is held in genes whose vital timing in switching on and off is orchestrated by a host of proteins expressed by other genes.