Evolution does not proceed in mighty anatomical jumps but through a process of gradual change, by transforming – very slightly – a gene, cell or bone so that it acts to a new purpose. In this way, a new species is eventually created, albeit one that still carries the hallmarks of its evolutionary predecessors. This inner connection stretches over the aeons, from fish to humans.
Neil Shubin (http://www.neilshubin.com/books.html and http://en.wikipedia.org/wiki/Neil_Shubin) explains how we can see these biological stigmata today. ‘Our hands resemble fossil fins, our heads are organised like those of long-extinct jawless fish and major parts of our genome still look and function like those of worms and bacteria.’ We are all shark siblings, in short.
The thesis is intriguing and although not entirely new, it is made fresh and accessible by Shubin’s laidback, rather chatty style, not to mention his admirable sense of the ridiculous and his catalogue of dotty anecdotes – an Arctic fossil dig turned to panic at the sight of approaching polar bears that, on closer inspection, were revealed to be large Arctic rabbits, and the marooning of his team on a remote Canadian river bank where they promptly found, by fluke, the fossil of a tritheledont, an extraordinarily rare, 200-million-year-old ‘part mammal, part reptile’.
Through this narrative Shubin, a paleontologist and evolutionary biologist at The University of Chicago (http://www.uchicago.edu/), outlines his case for the imprint of our aquatic ancestors. The evidence is in the form of fossil amphibian fins that demonstrate a structural affinity with human hands; teeth, first discovered in ancient jawless fish, that evolved into modern mammary and sweat glands; and genes, which control our eyes and ears, that correspond directly to DNA found in primitive jellyfish. If nothing else, the scope of Your Inner Fish is certainly ambitious. The real value of this book goes beyond biology. In demonstrating how anatomical features are co-opted in the natural selection of species, the author demolishes the concept of ‘intelligent design’. From the pages of Your Inner Fish, it is clear that if a supreme being were responsible for creating life on Earth, his work would be actionable in a court of law. Far from being the perfectly crafted handiwork of a deity, our bodies are jerry-rigged patchworks of old bones, cells and genes bolted on to old frameworks that creak and groan at every opportunity. Men suffer hernias because their spermatic cords, inherited from ancient fish ancestors, leave them susceptible to gut tissue spilling through muscle walls, for example, while the evolution of the voice box has left us vulnerable to all sorts of breathing and swallowing ailments. Or consider hiccups. Spasms in our diaphragms, hiccups are triggered by electric signals generated in the brain stem. Amphibian brain stems emit similar signals, which control the regular motion of their gills. Our brain stems, inherited from amphibian ancestors, still spurt out odd signals producing hiccups that are, according to Shubin, essentially the same phenomenon as gill breathing. Similarly, modern lifestyles leave us vulnerable to predispositions to obesity, heart attacks and haemorrhoids because we have the genes of hunter-gatherers who lived active, not sedentary, lives. Then there is our sense of smell. Three per cent of our DNA is devoted to receptors that give us a sense of smell. The same is true for all other mammals, including rats, dogs and cats, except that in humans, a third of this material, the equivalent of about 300 genes, has been rendered useless by recent mutations. We no longer rely on our sense of smell, so its genetic roots have atrophied.
So if we are created in a divine image, why fit us out with hundreds of useless, redundant smell-receptor genes in the first place? It’s hardly the handiwork of a supremely intelligent designer. For an infallible deity, God appears to have made an awful hash of corporeal design. The simpler explanation is that we are the products of a long and convoluted evolutionary history. Shubin makes his case well and I, for one, am happy to cherish the fish within!
256 pages in Penguin paperback edition
ISBN 978-0141027586
Neil Shubin