4.2 Caveat lector

It is easy to read Origin and satisfy oneself that co-dynamic interaction across two space-time scales (event and conjuncture) generates emergent, species-like patterns on a third, deep-time scale. It is also easy to establish that non facit saltum seems to imply almost-linear dynamics and time-asymmetry. Descent explicitly couples two of these three-level Darwinian systems, each with a different space-time signature, and uses them to explain the emergence of co-operative and compassionate behaviour. But we have no reason to believe Darwin would have found our account of selective fields, cross-scale lock-in, negative feedback and emergence helpful. He was certainly not interested in circumstances where evolution could become gridlocked by cross-scale lock-in and negative feedback, and resisted all attempts to persuade him to relax those continuity assumptions and admit the possibility of stick-slip dynamics.

Thomas Henry Huxley, who by this time was convinced that non facit saltum had been a mistake, would probably have been more alive to the possibility that multi-scale dynamics could become grid-locked in a way that would generate a saltatory dynamic, but Huxley was no theoretical biologist. He was scathing in his rebuttal of theory, describing logical consequences as 'scarecrows for fools and signposts for wise men' (Huxley 1874). His approach to evolutionary dynamics was empirical.

Darwin and Huxley did not anticipate developments in 20th-century complexity theory, but they had operationalised all the concepts needed to describe situations where pairs of evolutionary systems, each with its own hierarchy of three-level dynamics, could either interfere with each other to create a gridlock of cross-scale constraints or reinforce each other to emerge as a new species of dynamic system. However, it took biologists the better part of 100 years to put all these pieces together and get the model past the paradigmatic veto and into publication (Eldredge and Gould 1972; Gould and Eldredge 1977). Once such a model is in place, it becomes possible to explore the scope for locally linear, equilibrium-seeking dynamics punctuated by symmetry-breaking events and synergetic multipliers that allow new types of system dynamics to emerge in that characteristic, non-linear way.