Of all that surrounds us, life seems to be the most inexplicable. We are used to the fact that it is always around us and in ourselves, and we have lost the ability to be surprised. But go into the forest, look as if you were seeing them for the first time, at the trees, grass, flowers, birds and ants, and you will be overcome by a feeling of helplessness in the face of the great mystery of life. Is there really something in common in all this, something that unites all living beings, whether it be a person or a microbe invisible to the eye? What determines the continuity of life, its rebirth again and again from generation to generation? These questions are as old as the world, but it was only in the second half of the 20th century that it was possible to get answers to them for the first time, which, in fact, turned out to be not too complicated and, most importantly, dazzlingly beautiful. How they were obtained and what they consist of is described in this book. The central place in the science of molecular biology, which is designed to answer the eternal question: "What is life?", is occupied by the DNA molecule. It will be mainly discussed. The author paid much attention to those questions in the solution of which physics and mathematics play a particularly important role. This distinguishes this book from many others devoted to DNA.