Mitchell Ryan Distin

Change is the fundamental idea of evolution. Explaining the extraordinary biological change we see written in the history of genomes and fossil beds is the primary occupation of the evolutionary biologist. Yet it is a surprising fact that for the majority of evolutionary research, we have rarely studied how evolution typically unfolds in nature, in changing ecological environments, over space and time. While ecology played a major role in the eventual acceptance of the population genetic viewpoint of evolution in the synthetic era (circa 1918-1956), it held a lesser role in the development of evolutionary theory until the 1980s, when we began to systematically study the evolutionary dynamics of natural populations in space and time. As a result, early evolutionary theory was initially constructed in an abstract vacuum that was unrepresentative of evolution in nature. The subtle synthesis between ecology with evolutionary biology (eco-evo synthesis) over the past 40 years has progressed our knowledge of natural selection dynamics as they are found in nature, thus revealing how natural selection varies in strength, direction, form, and, more surprisingly, level of biological organization. Natural selection can no longer be reduced to lower levels of biological organization (i.e., individuals, selfish genes) over shorter timescales but should be expanded to include adaptation at higher levels and over longer timescales. Long-term and/or emergent evolutionary phenomena, such as multilevel selection or evolvability, have thus become tenable concepts within an evolutionary biology that embraces ecology and spatiotemporal change. Evolutionary biology is currently suspended at an intermediate stage of scientific progress that calls for the organization of all the recent knowledge revealed by the eco-evo synthesis into a coherent and unified theoretical framework. This is where philosophers of biology can be of particular use, acting as a bridge between the subdisciplines of biology and inventing new theoretical strategies to organize and accommodate the recent knowledge. Philosophers have recommended transitioning away from outdated philosophies that were originally derived from physics within the philosophical zeitgeist of logical positivism (i.e., monism, reductionism, and monocausation) and toward a distinct philosophy of biology that can capture the natural complexity of multifaceted biological systems within diverse ecosystems—one that embraces the emerging philosophies of pluralism, emergence, and multicausality. Therefore, I see recent advances in ecology, evolutionary biology, and the philosophy of biology as laying the groundwork for another major biological synthesis, what I refer to as the Second Synthesis because, in many respects, it is analogous to the aims and outcomes of the first major biological synthesis (but is notably distinct from the inorganic and contrived progressive movement known as the extended evolutionary synthesis). With the general development of a distinctive philosophy of science, biology has rightfully emerged as an autonomous science. Thus, while the first synthesis legitimized biology, the Second Synthesis autonomized biology and afforded biology its own philosophy, allowing biology to finally realize its full scientific potential.

Evolvability—which, in its broadest sense, means any causal factor that influences an evolutionary system’s ability to evolve (e.g., epistatic interactions, constraints, standing genetic variation)—could be the most significant addition to evolutionary theory since neutral theory in the 1980s, and Hansen and colleagues’ Evolvability: A Unifying Concept in Evolutionary Biology? (2023) is a major step forward for the maturation of the concept of evolvability. According to Hansen and colleagues, since evolvability research exploded onto the scene in the 1990s, the concept has developed divergently within the fields of evolutionary developmental biology, evolutionary quantitative genetics, paleobiology, and computational biology. No comprehensive attempt has so far been made to synthesize the expansive plurality of conceptions of evolvability. For this reason alone, I believe Hansen and colleagues' Evolvability: A Unifying Concept in Evolutionary Biology? (2023) is the steppingstone from which all future conceptual and empirical research on evolvability must build on. However, despite the acknowledged success of Hansen and colleagues (2023), the onerous tasks of maturing the concept of evolvability and successfully integrating it into modern evolutionary theory are now within reach but are still left incomplete.

Advances in the empirical sectors of biology are beginning to reveal evolvability as a major evolutionary process. Yet evolvability’s theoretical role is still intensely debated. Since its inception nearly thirty years ago, the evolvability research front has put a strong emphasis on the non-genetic mechanisms that influence the short-term evolvability of individuals within populations by causing phenotypic heterogeneity, such as developmental trait plasticity, phenotypic plasticity, modularity, the G-P map, robustness, and/or epigenetic variation. However, genetic evolvability mechanisms such as mutation or recombination have a deeper history in evolutionary thought that is often overlooked by those in the evolvability research front, with recent evidence suggesting that species switch to genetic evolvability mechanisms when short-term evolvability strategies fail to relieve selective pressures. For this reason, a causal distinction must be made between genetic evolvability and the more recently emphasized non-genetic (or evo-devo) evolvability to allow for its maturation as a central explanatory concept. I conclude by arguing that the anachronisms of the scientific process are the main culprit behind recent divisions in biology and likely beyond. To streamline theoretical progress, we need to build a new science with new underlying philosophies like restricted pluralism.