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18 march 2019
The first half of Jan Zalasiewicz and Mark Williams' Skeletons reads much like an old-fashioned up-the-evolutionary-ladder narrative, tracing the development of the animal skeleton from the dawn of life to the Anthropocene. Or not so much up-the-ladder as along-the-branches, because this section is structured much like the cladistically-organized hall of vertebrates at the American Museum of Natural History.
But then we get to Man the Upright halfway through, and one wonders: where do we go from here? Surely the pinnacle of creation – sorry, of natural selection – is achieved once you're bipedal and have opposable thumbs. But at that juncture, Zalasiewicz and Williams start to expand laterally from humans and their near-relatives to consider "skeleton" in its broadest possible senses. One begins to realize that the framework of the Earth itself is provided by a vast concatenation of the skeletons of living and once-living beings.
Arthropods and many other invertebrates have external skeletons, and vertebrates (and a few other creatures like sea urchins and starfish) have internal skeletons. But those animal frameworks provide just three of Zalasiewicz and Williams' ten chapters. From animals, they range to plants (considering wood as a type of skeleton, and noting the presence of silica in many plants in the form of phytoliths, which give many stalks and stems their toughness). They look at coral and other kinds of reefs, which form the backbones of many an island and outline entire continents at times: skeletons visible from space. They examine the tiniest of skeletons, those of plankton and meiofauna, which in a living example of the sorites paradox, amount to a staggering amount of biomass, one tiny organism at a time. They look at skeletons in the air and skeletons in the fossil record. Zalasiewicz has speculated elsewhere about the extremely far future of Earth and thus naturally speculates here about the kinds of skeletons that will provide fossils for observers long after we're gone. And the authors conclude with a look at possible skeletons on other worlds, which may take chemical or technological forms that would surprise us.
In other words, Skeletons is the kind of book that thinks outside the box, or the rib cage if you prefer. Its big-picture musings are just the thing to get your mind working about the realities that surround us, but are both too large and small, too ephemeral and too slow-moving, for us to perceive. The soil is full of worms, tiny skeletal creatures live between grains of sand, the seas are astonishingly alive, and the air itself is full of organisms – and most of them, if they grow large than a cell (and sometimes no larger), need some sort of hard structure lest they immediately be gobbled up by a better-armored neighbor. This is popular science at its best.
Zalasiewicz, Jan, and Mark Williams. Skeletons: The frame of life. Oxford: Oxford University Press, 2018.