The riddle of emergence – where do novel things come from?

It’s not true, that there’s nothing new under the sun. The universe is producing novelty all the time. Galaxies, stars, and planets, where none existed before. New elements, new molecules – life itself, with the explosion of new species, and eventually new minds, capable of new thoughts. New types of things at new levels of existence – discrete entities composed of smaller entities, arranged in specific ways. New systems with new properties and new causal powers, governed by new principles. So where does all this novelty come from?


The term emergence is often used to refer to the appearance of qualitatively novel states or processes or properties that arise when things are combined in certain ways. But as with many metaphysical terms, it means different things to different people and in different contexts, and it’s not always clear what, if anything, follows from its use. In particular, it is often not stated whether “emergence” simply refers to an observed phenomenon in need of explanation, or is supposed to be an element (or even the entirety of) such an explanation.


If we take life, or example, we can say that it emerged in the universe. This is a straightforward description of what happened – it didn’t used to exist and now it does. In a slightly different way, to say that, at any moment, life as an ongoing activity of an individual organism is an emergent phenomenon also seems uncontroversial – living things are made of components that are not themselves alive, but a whole organism is. On a finer scale, it seems equally unproblematic to say that living things have a suite of emergent properties that are qualitatively different from those of their components.


These usages are fairly unproblematic, on their face at least, but they’re also not particularly enlightening. What is the term supposed to actually imply about the new properties or about the relationship between the components and the higher-level system? Is it simply that the “whole is more than the sum of its parts”? That seems trivial, or worse, nonsensical. How could it be otherwise? Almost by definition, “wholes” have properties that derive not just from the isolated properties of their parts but from the way those parts are organised (not “summed”, whatever that might mean). That’s what makes something an entity, as opposed to, say, a pile.


Then what else is the term emergent meant to imply? It hints at complexity, non-linearity, and irreducibility, at hierarchical relationships, where new levels exhibit novel kinds of behaviour, and may even exert some kind of macroscopic or whole-part or top-down causation back onto the whole system. Those properties actually sound objective enough – they’re the kinds of things that complexity and information theory often deal with and can even quantify (e.g., 1, 2, 3). But is that it? Is emergent a synonym for that kind of complexity? There seems to be an added element that warrants the usage of the term, one that hinges on something else entirely: subjective, observer-dependent properties, like unexpectedness, unpredictability, or even interestingness. It’s not just that a system has new properties – it’s that they’re surprising, maybe even impressive.


Strong and weak emergence


David Chalmers has an interesting article probing the senses of emergence, especially the supposed distinction between “strong” and “weak” forms. This hinges mainly on whether the new properties are thought to be unpredictable in principle (the strong version) or are merely unexpected or difficult for us to predict in practice (the weak version).


For Chalmers, consciousness provides the only convincing example of a truly emergent phenomenon, in the strong sense. Here, something qualitatively completely novel and entirely unpredictable emerges from systems arranged in a certain way. Subjective experience seems to pop into existence in a way that is almost magical. It’s not just that it is irreducible to the workings of the physical brain – it’s that it’s not deducible from those workings. Nothing about the physical details could predict that subjective experience should arise from them.


I’m not convinced that’s completely right, though. If you look at the trajectory of evolution of cognitive control systems, you can see how metacognition and recursive self-reference could quite naturally and adaptively evolve and be selected for. Indeed, you could make a strong case that their emergence was in fact predictable. That said, it’s still not obvious why recursive self-reference has to feel like something. So, consciousness (really subjective experience at all) still seems like our best candidate for a truly strongly emergent phenomenon (though I’d be inclined to put life and agency in that category too).


Chalmers’ discussion of weak emergence highlights the importance of the sense of unexpectedness: “To capture this, we might suggest that weakly emergent properties are interesting, non-obvious consequences of low-level properties. This still cannot be the full story, though. Every high-level physical property is a consequence of low-level properties, usually in a non-obvious fashion” …


He goes on to suggest that “weak emergence is the phenomenon wherein complex, interesting high-level function is produced as a result of combining simple low-level mechanisms in simple ways. I think this is much closer to a good definition of emergence.” … [Note a similarity here to the idea of global dynamics emerging purely from local interactions, with no top-down coordination or control].


However: “This conclusion captures the feeling that weak emergence is a ‘something for nothing’ phenomenon”…


Finally, he suggests that “an appeal to principles of design should get us the rest of the way. We design the game of Life according to certain simple principles, but complex, interesting properties leap out and surprise us.”


That “something for nothing” aspect seems to capture what people really mean when they use the term emergence. But it is also obviously the most problematic aspect of the notion. Both weak and strong emergence both suppose that the property that is taken to be emerging really did not in any sense exist before the system in which it is observed came to be arranged in that particular way.


Discovery, not invention


I think in many cases this is a mistake. The instances of supposed emergence that most catch our attention are those where it’s not just true that some new dynamics arise, but where they enable some new functionality in the system. This doesn’t have to mean that those dynamics are invented or created de novo – in many cases, especially in living systems, they are discovered. They don’t just emerge from the lower level organisation. Quite the opposite, in fact – they often reflect systems principles that simply hold in the abstract and that constrain the organisation of the lower level components (because they confer some adaptive functionality that becomes selected for).


Evolution is in the design game. But it produces functional designs by exploration and selection, not by raw creation from the void. It’s not just luck that living systems have the functionalities they do. The principles that enable them exist and can be found by evolution.


For example, there are certain configurations of elements and relations that will constitute a filter, an amplifier, an oscillator, a clock, an evidence accumulator, a coincidence detector, a logic gate; that will execute gain control, or divisive normalisation, or stochastic resonance; that will extract principal components, or drive a low-dimensional manifold, or perform Bayesian inference. Those motifs are seen in gene regulatory circuits, in biochemical signal transduction pathways, and in neuronal circuits and systems. And of course they’re seen in our artificial designs as well. The medium doesn’t matter – the functionality is abstract.  


The principles at play are the subject of fields like cybernetics and control theory and information theory, as well as dynamical systems theories that encompass the dynamics observed in living systems, of self-organisation, attractors, criticality, phase transitions, and so on. It’s interesting to ask, on a meta level, whether these theories are built of elements that are fundamental – Platonic truths that simply hold true – or are themselves emergent, in the weak sense that they can be derived from theories about simpler things.


But whether the underlying principles are ultimately fundamental or not, we can still say that many of the functional properties we observe as we go from level to level in living systems are not so new after all. They’re common in fact – shared across many kinds of systems at many different levels. It’s not a matter of getting “something for nothing” – it’s a matter of finding something useful and hanging on to it.


In these cases, it’s not obvious that the term emergence really applies or offers any useful insights. The crucial difference with, say, the complex and surprising dynamics observed in cellular automata, is that the configurations and dynamics observed in living things are for something. They’re not arbitrary. They’ve been selected for robust functionality. While they may still be astonishing, they’re not unpredictable in the same sense. There’s an understandable logic to why they are the way they are. They’ve been through the filter of natural selection, which is in the business of making predictions – predictions that the world will continue to be more or less like it was in the past, and that functionalities that promoted survival will continue to be adaptive in the future.


Living organisms are made of many such subsystems, collectively configured to promote the survival and reproduction of the organism. And the dynamics we observe at the level of higher systems (composed of many subsystems) are equally relatable to the same kinds of abstract functional design principles. Evolution has explored that space of functionalities at each level and selected the ones that confer adaptive advantages. There is scope in this process for real novelties to arise, through new combinations of these functional primitives, but this still comes about through a process of exploration and selection, rather than naïve emergence. The novel functions don’t just pop into existence spontaneously or come for free – evolution has to do some design work to find and retain them.



Emergent dysfunction


To put a little twist in the tail, there is I think a paradoxical corollary to this way of thinking. While the functionalities embodied in the configurations of living systems have been selected for and are thus not arbitrary or unanticipated, patterns of dysfunction may well be. Natural selection will favour configurations that work and that confer some selective advantage. Along some lineages, that can lead to complexification of systems, notably the nervous system. The new selective advantages that come with increasingly sophisticated cognition may be strongly selected for, but the downside is that as systems get more complex, they may develop more ways to fail. Selection for robustness may not keep pace with selection for new or improved function.


The result, in our own species, may be a propensity for a minor proportion of individuals to develop emergent states of brain function that we recognise as psychopathology. Many psychiatric conditions are quite highly heritable, and seem to reflect the impact of genetic variants on the program of brain development. The striking aspect of many of the emergent pathological states is their qualitative novelty. We might simply have expected such insults to lead to either general or more specific decrements of cognitive functions. Instead, we get novel states like psychosis or mania or obsessive-compulsive disorder – not just less function, but a shift to a different regime altogether. In my book, such states – ones that are unanticipated outcomes of insults to complex systems selected for other functions – really do warrant being called emergent. (In line with the literature on “emergent failure modes” in systems engineering).


And in this case, thinking of pathological states in that way has important implications for how we think about the (very indirect and non-specific) relationship between gene functions and psychiatric symptoms.




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