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1. A really good book on the Cambrian Explosion of life forms is Stephen Jay Gould’s Wonderful Life
   (1989) — written for a non-scientific audience.

   Especially amusing is the description of the puzzles that discoverers had to solve when looking at the preserved fossils found in the Burgess Shale in Canada. What they assumed were the heads of animals turned out to be their rear ends; what they assumed were legs turned out to be spikes; what they assumed were two or three different creatures mashed together turned out to be one single creature — hence the names Anomalocaris and Hallucigenia. You can almost hear their frustration, in the names!

   Suppose that we could replay life’s tape from late Precambrian times, and that the flat quilts [body shapes] of Ediacara won on their second attempt, while metazoans [the cretures we’re descended from] were eliminated. Could life have ever moved to consciousness along this alternative pathway of Ediacara anatomy? Probably not. Ediacara design looks like an alternative solution to the problem of gaining enough surface area as size increases. . . . Modern life followed the path of evolving internal organs . . . to provide the requisite surfaces. . . . In a second solution, . . . organisms may not be able to evolve internal complexity. . .

   If Ediacara represents this second solution, and if Ediacara had won the replay, then I doubt that animal life would have ever gained much complexity, or attained anything close to self-consciousness. The developmental program of Ediacara creatures might have foreclosed the evolution of internal organs, and animal life would then have remained permanently in the rut of sheets and pancakes — a most unpropitious shape for self-conscious complexity as we know it.

   …

   Wind the tape of life back to Burgess times, and let it play again. If Pikaia [the first known creature with a spinal cord] does not survive in the reply, we are wiped out of future history — all of us, from shark to robin to orangutan. And I don’t think that any handicapper, given Burgess evidence as known today, would have granted very favorable odds for the persistence of Pikaia.

   And so, if you wish to ask the question of the ages — why do humans exist? — a major part of the answer, touching those aspects of the issue that science can treat at all, must be: because Pikaia survived the Burgess decimation. This response does not cite a single law of nature; it embodies no statement about predictable evolutionary pathways, no calculation of probabilities based on general rules of anatomy or ecology. The survival of Pikaia was a contingency of “just history.”

   — Gould

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   • Just one easy question. Which came first, the single-cell protozoan, or DNA?

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     • Only God knows.

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