8.1 By the mid nineteenth century several scientific currents were causing a profound change in man’s understanding of his relation with nature. Copernicus, Kepler and Galileo had shown Mankind was no longer the centre of the universe. Newton had begun to show how a few powerful laws governed motion throughout the universe. Humboldt had electrified the world with his exploration of nature, gathering a vast amount of evidence of not just the variety of nature, but the surprising similarities found across the world.

8.2 The great age of the earth was beginning to be appreciated as Hutton and Lyell showed how small changes over vast tracts of time could have produced the similar layers of rock formations seen throughout the world. Whole extinct prehistoric worlds had been discovered and demonstrated by Cuvier with fossils of animals unknown to man. And then Linnaeus had supplied the tools for scientists across the world to discover, document and disseminate their ideas about the family relationships between species. But great as their contributions were to the study of nature, neither Linnaeus or Cuvier strayed from their detailed and meticulous observation of the variety of species, living and extinct, to venture an explanation of how this variety came about. Still the law of motion of living nature evaded science. However, there were some intriguing suggestions, for instance from James Hutton, who had even suggested natural selection as a possible mechanism affecting the adaption of life forms to their environment:

"...if an organised body is not in the situation and circumstances best adapted to its sustenance and propagation, then, in conceiving an indefinite variety among the individuals of that species, we must be assured, that, on the one hand, those which depart most from the best adapted constitution, will be the most liable to perish, while, on the other hand, those organised bodies, which most approach to the best constitution for the present circumstances, will be best adapted to continue, in preserving themselves and multiplying the individuals of their race." – Investigation of the Principles of Knowledge, volume 2.

8.3 Richard Dawkins raises the question: What delayed humanity’s tumbling to that luminously simple idea which seems, on the face of it, so much easier to grasp than the mathematical ideas given to us by Newton two centuries earlier? In answer he suggests Ernst Mayr’s reason: it was not ignorance, but the presence of another fundamental concept, Platonic essentialism, which blinkered scientists – the idea that all mortal creatures are but mere shadows of their ideal essences. Or put another way, all creatures great and small were created in one original, perfect form.

8.4 Georges Cuvier, surprisingly given his otherwise profound insight into the history of life on earth, is a good example.  The notion that animals could change their body types when convenient Cuvier found absurd.  He lampooned the idea that “ducks by dint of diving became pikes; pikes by dint of happening upon dry land changed into ducks; hens searching for their food at the water’s edge, and striving not to get their thighs wet, succeeded so well in elongating their legs that they became herons or storks”  He was attacking the current best notion of how species came about, the idea of transformisme  championed by his senior colleague at the Museum of Natural History Jean-Baptiste Lamarck. 

8.5 Cuvier’s counter argument was a version of Platonic essentialism.  At the heart of his understanding of anatomy was a notion he termed “the correlation of parts”.  By this he meant that the components of an animal all fit together and are optimally designed for its particular way of life.  For instance an animal with hooves must necessarily be a herbivore, since it has “no means of seizing its prey”.  Were any one of these parts to be altered, the functional integrity of the whole would be destroyed. An animal that was born with, say, teeth or sense organs that were somehow different from its parents’ would not be able to survive, let alone give rise to a whole new kind of creature.

8.6 Having dismissed transformisme – the notion that one species could change to another in response to their environment, Cuvier was left with a gaping hole. He had no account of how new organisms could appear, nor any account of how new organisms could appear, nor any explanation of how the world could have come to be populated by different groups of animals at different times.

8.7 So surrounded by deeply ingrained philosophical antipathy to the notion of evolution, fervent religious animosity and the withering opinion of at least one of the leading scientists of the age, it is not surprising that Darwin stepped carefully as he trod the path in search of the unifying law behind the development of all forms of life, everywhere in all time. And so it was to take him more than twenty years from when he first sketched a tree of life in his notebook and doodled the words "I think" before he published "On the Origin of Species" in 1959 with what Daniel Dennett has described as the single best idea anyone had, ever.

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