Wills is a biologist and the author of many accessible books, such as The Runaway Brain, while Bada is a director of exobiology research at NASA. They have joined forces here to provide an engaging account of one of the greatest questions we can ask: how did life begin?

The book is subtitled Darwin and the primeval soup, yet Darwinism is about how living things evolve: about the origin of species, not the origin of life itself. Here is yet another instance of how profoundly valuable Darwin's idea is. The authors show how a kind of proto-Darwinism could throw light on the earliest days of biochemistry, given that evolution is "extremely good at sorting things out":

"It is difficult for us to imagine any sort of Darwinian evolution in the absence of genes. But if the sorting-out capability could somehow be de-coupled from the reproductive capability, then at least some aspects of Darwinian evolution might apply to molecules other than genes." (p.111)

DNA is a familiar enough item for anyone who reads newspapers, and RNA may be recalled from school science lessons. PNA is a newcomer: peptide nucleic acid was put together by Danish researchers, who were trying to make a simple kind of nucleic acid that would bind to parts of the RNA of the AIDS virus and block its replication. It is replication, though, that is the key element of any feasible model of how we got from plain old chemistry to biochemistry, the stuff of life.

By the time we reach PNA, we are half-way through the book, and have enjoyed huge journeys through both the history of the Earth and the history of science. We are then introduced to another charming possibility: the spreading-slime hypothesis, whereby some kind of accumulation of molecules and their differential deaths may have paved the way for those bags of chemicals thought to be precursors of the first cells.

Later on we encounter SLiME: Subsurface Lithoautotrophic Microbial Ecosystem, which denotes communities of bacteria apparently thriving deep inside the rock of the Earth's crust. These organisms might have no need of energy from the Sun, living instead on hydrogen and other gases. This kind of possibility leads to discussions of life on other planets and places, such as in the sub-surface oceans of some of Jupiter's moons.

Researchers have not yet reached the point where some kind of proto-Darwinism can accelerate the development of life in a test-tube. The authors conclude this engrossing survey of testable ideas about the origins of life with these words:

"...life on Earth is not some unlikely accident. Life may even have appeared more than once during the early history of our planet. And it is hard to imagine [is it?] that it has not appeared in many other parts of the universe . Soon, we are confident, it will appear in a test tube. And our world will never be the same." (p.260)