Mendel's Demon ensures this. This book covers the whole history of life. It cuts a wide swath. Ridley argues that life, rather than being a most unlikely, freakish accident, is highly probable, given the chemistry of the prebiotic earth. Part of his evidence is the short interval between the origin of the earth and the appearance of life.
Life is probable, complex life improbable.
If there is life elsewhere, or if our own tape had been rerun, complexity may well not have arisen. The essence of life is the capacity to evolve by natural selection. In successive chapters, Ridley discusses the role of selection in the evolution of gene number, mutational meltdown, and adjustment of mutation rates. Surprisingly, there has not been much change in the frequency of mutational errors since the origins of multicellularity. A major change in complexity was evolution of the eukaryotic cell, containing seperate nuclear, mitochondrial, and plastid systems.