It has become a cliché to say that when Charles Darwin published On The Origin of Species in 1859, he turned our view of the world on its head. But this is quite literally the case, for as the philosopher Daniel Dennett explains in his absorbing read Darwin’s Dangerous Idea, Darwin’s theory of evolution threatened to invert the ‘cosmic pyramid’ or ‘great chain of being’ (that traditionally placed God at the top, Creator of all things), by suggesting that design, or at least a semblance of it, could manifest by itself out of mere ordered matter if only given time. This, of course, was the philosophical implication, but Darwin himself was far more modest in his writing, diligently side-stepping the loaded question of how life itself began to demonstrate how the wonderful variety of life on Earth could have descended from earlier, simpler, pre-existing organisms through an algorithmic process he dubbed natural selection, and which avoided the need for an omniscient Creator, guiding the process along.
Despite over 150 years of accumulated evidence, the truth of evolution is still difficult for many people to accept, but nowhere in our exhibitions are its paradigm-changing qualities more succinctly expressed than in this fascinating (and quite frankly, bizarre) artwork by William Cobbing, on display in Medicine Now. Entitled ‘Palindrome’, it is a modified artificial skeleton of a human, with its parts reversed – it has a skull for a pelvis, and a pelvis for a skull. ‘What has this got to do with evolution?’ I hear you say. Well, when it comes down to it, rather a lot.
Cobbing was inspired by a book by the late author J. G. Ballard, ‘The Atrocity Exhibition’, wherein one of the characters, a doctor called Travis, imagines that ‘the bones of the pelvis may constitute the remains of a last sacral skull.’ In a scientific sense this is utter tripe, but what Cobbing has quite cleverly revealed in this artwork is that many parts of our bodies, when they originally evolved in our ancestors, may have served a very different purpose. Genetic research has suggested that our fingers and toes, for instance, may have originally evolved as the fins of fish that swam in the oceans over 100 million years ago. If this seems completely ridiculous, then genetics has shown the very same genes are perhaps responsible. An innocuous-sounding gene called HoxD-13 is present both in the DNA of four-limbed animals with a spinal cord (tetrapods), and a type of antipodean fish called Australian lungfish. In the fish, it controls the growth of the upper fins from the lower fins, but in animals, it controls the growth of fingers and toes from hands and feet, or claws from paws elsewhere. (Mutations in this gene are known to lead to the development of fused or extra digits.) The ubiquity of this gene means that it is highly unlikely it evolved independently in every single species that possesses it. Rather, it eludes to the common descent of all tetrapods (including us) from organisms that swam in our seas hundreds of millions of years ago.
Clues to our fishy ancestry also come from evolutionary developmental biology. Even without knowledge of DNA, genes or chromosomes, Darwin knew that embryonic development provided a tantalising hint as to our evolutionary origins. In The Descent of Man (1871), Darwin compared the embryos of dogs and humans at equivalent stages of development to demonstrate our (albeit distant) common ancestry. He pointed out the atavisms or evolutionary throwbacks expressed in foetuses that betray our common ancestry, which are later hidden as the embryo develops further, such as an ancestral tail. We now know that as fish and human embryos develop, genes are activated which control the development of structures called pharyngeal arches. In humans they become part of the pharynx, but in fish they go on to support the gills (this observation has led to the rather amusing assertion that human embryos have gills, which, I’m sorry to report, is not the case).
In a slightly different sense, our genome is chock-a-block with palindromes – sequences of DNA bases that read the same back to front, and which have been linked with the multiplication of oncogenes, genes responsible for cancer.
Chris Sirrs is a Visitor Services Assistant at Wellcome Collection. Look out for our special ‘Darwin’ themed tours of the Medicine Man and Medicine Now galleries on the Wellcome Collection tours page.