The Sleepwalkers: A History of Man's Changing Vision of the Universe

by Arthur Koestler

New ideas are thrown up spontaneously like mutations; the vast majority of them are useless crank theories, the equivalent of biological freaks without survival-value. There is a constant struggle for survival between competing theories in every branch of the history of thought. The process of ‘natural selection’, too, has its equivalent in mental evolution: among the multitude of new concepts which emerge only those survive which are well adapted to the period’s intellectual milieu. A new theoretical concept will live or die according to whether it can come to terms with this environment; its survival value depends on its capacity to yield results. When we call ideas ‘fertile’ or ‘sterile’, we are unconsciously guided by biological analogy. The struggle between the Ptolemaic, Tychonic, and Copernican systems, or between the Cartesian and Newtonian views of gravity, was decided by those criteria. Moreover, we find in the history of ideas mutations which do not seem to correspond to any obvious need, and at first sight appear as mere playful whimsies – such as Apollonius’ work on conic sections, or the non-Euclidian geometries, whose practical value became apparent only later. Conversely, there are organs which have lost their purpose and are yet carried over as an evolutionary legacy: modern science is full of appendices and rudimentary monkey-tails.