A popular riposte to the idea of evolution is the so-called ‘argument from design’. The discovery of a pocket watch on a hillside leads naturally to the inference of the existence of a watchmaker. The intricacy of its many elegantly machined parts, all working together so harmoniously to tell you the time, speaks of organisation and planning. And so, when we see the many examples of beauty and perfection in the natural world, we must, by analogy, infer the existence of a cosmic designer. The elegance of the natural world – how bees, for example, are supremely adapted for pollination, or cats for catching mice, or the human eye for seeing – speaks strongly to this appearance of design. 

As science has progressed from natural history down to the microscopic world, design seems all the more evident. Consider the small set of genes in the common gut bacterium Escherichia coli, which switch themselves on in the presence of lactose, all the better to digest it, but switch themselves off