By Neil Shubin
Allen Lane £20, 240 pages
FT bookshop price: £16
If you want to understand the evolutionary history of man and other animals, and read no other account this year, read this splendid monograph. And if you subscribe to “creationist” tendencies, read it also and repent your sorry ways.
In 240 profoundly fascinating pages, Neil Shubin, fossil-hunter, comparative anatomist and developmental zoologist, explains the origins of the constituent parts of every living body. He traces the tortuous path from the simple, free living cells which fought for survival in the primeval slime to the most sophisticated animal known to science: man.
On the way, he explains the mechanism of evolution in a manner which makes it instantly comprehensible and gives the lie to those who would claim that life is too complex to have arisen by chance. He also explains why the eyes of the inebriated slide inexorably to the right (it's called nystagmus) and how he panicked at two in the morning in a laboratory with 25 dead bodies for company, inadvertently locking his house keys in the lab as he fled.
Your Inner Fish is, perhaps, a rather trite title for such a magisterial work. It refers to Shubin's contention – and indeed the contention of most evolutionary biologists – that life began in the sea, evolving over billions of years to create fish-like creatures. Some of which took to the land to avoid their predatory contemporaries; hard teeth, all the better to bite and dismember the prey, evolved before hard skeletons. All mammalian organs, he argues, can be traced back to their fishy equivalents.
Shubin's basic proposition is encapsulated in what he calls the biological “law of everything”: that every living thing on the planet has parents. This innocuous, quite banal statement conceals a great profundity: that no structure in the living world arises de novo. And not only every creature but also every limb, every organ and every tissue is derived from an earlier form – and in the process, may go through a transformation which renders the relationship between one and the other hard to understand.
He describes, for example, the discovery of the origin of the bones of the mammalian middle ear. Comprising three separate bones, the malleus, the incus and the stapes, this structure is unlike that of any other class of animal: reptiles and amphibians have one bone while fish have none. So where, Shubin asks, did our middle-ear bones come from? The answer was provided in 1837 by the German anatomist Karl Reichert. He had been following the development of gill arches, swellings around the base of the embryonic head, in mammals and reptiles. He was astonished to find that two of the ear bones in mammals corresponded to pieces of the jaw in reptiles. Shubin writes: “The conclusion was inescapable: the same gill arch that formed part of the jaw of a reptile formed ear bones in mammals. Reichert proposed a notion that even he could barely believe – that parts of the ears of mammals are the same thing as the jaws of reptiles”.
As a fossil hunter, Shubin distinguished himself by leading an expedition to the Arctic in 2004 which uncovered the remains of a fish with a wrist, a creature with part fin, part limb. Named Tiktaalik (Inuktitut for “large freshwater fish”), it was the first fossil to show characteristics which placed it midway between land and sea; in its time, Tiktaalik probably propelled itself along the bottom of streams and ponds or navigated mudflats along the riverbank, supporting its body on its strange, limb-like fins.
We all suppose that fossils are found by accident. Hill walkers find dinosaur bones sticking out of hillsides: schoolchildren pick up ostracoderm skeletons on the beach. And such discoveries do happen. But Shubin explains that the professionals do all they can to weigh the odds in their favour. Expeditions are planned in as much detail as a military campaign. The hunters choose their terrain carefully, looking for rocks of the right age, the right type to preserve fossils and rocks that are exposed at the surface. But even he admits that serendipity plays a big part in a successful hunt.
Shubin's book is packed with the evidence to support his contention that everything innovative or apparently unique in the history of life “is really just old stuff that has been recycled, recombined, repurposed or otherwise modified for new uses”. It's not a new notion, but rarely has it been expressed so clearly and with such good humour.
Alan Cane is the FT's science correspondent.
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