Darwin’s central idea is fantastically simple. In its most distilled form, it reflects the principle that things which are best equipped to stick around tend to, well, stick around. What many find difficult to wrap their heads around is how such a simple process could have resulted in creatures so mind-bogglingly complex that they produce theories of their own existence–and then argue over them. Could a seemingly blind and purposeless process, unknowingly chugging along across eons, result in the miraculous and self-aware phenomenon of Twitter warfare exhibited today by specimens of evolutionary theorist?

Modern estimates have it that your ancestors may have spent their first two billion years of existence bumbling around the mouths of deep-sea volcanoes as some sort of proto-bacterial sludge. The eventual transition to eukaryotic life occurred when primitive prokaryotic cells were sequestered by an enveloping membrane, and their independent functions became subservient to a higher-level autonomy. This new form of cellular life found itself much better equipped to exploit the resources of its environment. Fast-forward another billion or so years to the origin of multicellular life, and a similar pattern emerges: the sacrifice of lower-level autonomy in the service of synergistic outcomes at a supervening level. John Maynard Smith and Ëors Sathmáry were the first to draw attention to such significant discontinuities in evolutionary history as the origins of chromosomes, multicellularity, sex, eusociality, and language, terming them major transitions.

Over the long history of life on earth, the most consequential events have been those in which organisms came to embody new levels or modalities of existence. This poses an explanatory problem for orthodox Darwinism. The question becomes, if natural selection is a process incapable of anticipating effects from causes, how do we account for repeated transformations in which functionality is apparently sacrificed in favor of effects unanticipatable from the perspective of genes, organisms, or evolution itself. If we could describe such a mechanism, would it act alongside (or intermittently with) that of natural selection, subsume the mechanism of natural selection, or would it be encompassed by the mechanism of natural selection? Does the mechanism of major or hierarchic transitions supply a new causal model of evolution, or merely add explanatory nuance to our existing model of evolution by natural selection?

Over the years, evolutionary theorists have posed a variety of mechanisms to account for these transitions, few with the success or conceptual rigour of Terrence Deacon. Deacon’s model begins with the duplication of a functional element within the evolving system, leading to redundancy. Relaxation of selective pressures which maintain the function of one such redundant element leads its function to degrade. The function of this component is allowed to wander, in effect, conducting an exploration of possibility space. As the function of the redundant component freely morphs away from its prior occupation, it may assume a functional role complementary to the role of its non-degraded counterpart. What emerges is a synergistic dynamic at a higher level. Selection will then act to maintain this newly distributed function, or higher-order autonomy.

Deacon’s account provides a mechanism by which lower-level autonomy might plausibly be sacrificed to produce synergistic dynamics at a higher level without recourse to any prior anticipation of complementation or synergistics. Though Deacon’s model of hierarchic transitions in no way contradicts the tenets of evolution by natural selection, it may supply a new and critical piece to the grand puzzle of how the complexity of you and me could have grown out of inert matter.

To learn more about Deacon’s work on hierarchic transitions, you can check out the lecture he gave on the topic for the EvoS Seminar Series: