The evolutionary unfolding of life on Earth is a breathtaking story. Driven by the creativity inherent in all living systems, expressed through three distinct avenues – mutations, the trading of genes, and symbiosis – and honed by natural selection, the planet's living patina expanded over billions of years and intensified in forms of ever-increasing diversity. The story has been told many times. For a beautiful, detailed, and sophisticated account we recommend the book Microcosm by Lynn Margulis and Dorion Sagan (1986). Rather than retelling the whole story, we shall concentrate on its beginning, the origin of life, in this chapter, and on its most recent stage, the evolution of the human species in Chapter 11.

Oparin's molecular evolution

What can science say about the origin of life on Earth? It is fair to say from the start that we do not have an answer to the question on how life originated on Earth. It remains one of the great mysteries on scientists’ agenda. It is generally accepted that life on Earth originated from inanimate matter via a very long series of chemical steps which brought about a spontaneous and continuous increase of molecular complexity and functionality, until the emergence of the first compartmentalized structures (protocells) capable of making copies of themselves at the expense of their surroundings (see Figure 10.1). It was a Russian chemist, Alexander I. Oparin (1894–1980), who put these ideas in writing, in a short, seminal book, The Origin of Life, published in Moscow in 1924.