Book excerpt: Spontaneous generation of living organisms-life arising without progenitor or seed-was a common belief in the time of Aristotle. Over the next two thousand years, support for spontaneous generation slowly retreated to its final stronghold: spontaneous formation of the first living organism. From recently acquired insights into the complexity of the simplest organisms, Tan and Stadler specify requirements for spontaneous formation of life and evaluate the prospects for natural processes to satisfy these requirements. The Stairway to Life is a thought-provoking inquiry that breaches the final stronghold of spontaneous generation.