Evolutionary Transitions

The evolution of life in our biosphere has been marked by several major innovations. These major complexity shifts include the origin of the genetic code, cells, symbiosis, multicellularity and programmed death, up to the emergence of non-genetic information, sight, language or even consciousness. Understanding the nature and conditions for their rise and success is a major challenge for evolutionary biology. Each of these transitions involved the integration of autonomous elements into a new, higher-level organization whereby the formerly isolated units interact in novel ways, losing their original autonomy.

The pioneering work of Maynard Smith and Szathmáry provided a well-defined set of case studies in which some regularities are common to all transitions: a reduced replicative potential of the units that now belong to a higher-order entity, the emergence of division of labour, and the presence of new forms of dealing with information. But a fundamental question remains open: are these transitions unique, rare events, or do they instead have universal traits that make them almost inevitable when the right pieces are in place? Are there general laws of evolutionary innovation?

In order to approach this problem under a novel perspective, we have proposed the concept of Synthetic Major Transitions as a unifying framework. The idea is that a parallel class of evolutionary transitions can be explored involving the use of artificial evolutionary experiments where alternative paths to innovation can be studied. Using synthetic biology, evolutionary robotics and artificial life, we can recreate past biological events but also explore alternative possibilities — transitions that are not necessarily related to standard evolutionary paths, but that do involve ways to generate major innovations starting from simpler systems.

Among our current projects, we study pathways leading to synthetic multicellular aggregates exhibiting fitness advantage under given environmental conditions, combining both genetic engineering and experimental evolution. Multicellularity is a crucial innovation that has taken place independently at least 25 times in the history of life on our planet. Uncovering the rules associated with this transition has been partially achieved through comparative biology, palaeobiology and genomic studies, but an alternative path is the use of synthetic approximations. We have shown, for example, that simple models involving multistability, differential adhesion and selective environments can lead to the emergence of proto-organisms with nested substructures and internal environments — the basic ingredients of organismality.

At the origins-of-life end of the spectrum, we study protocell dynamics, the emergence of early replicators and cooperators, error thresholds and information loss, and the potential for "order for free" as the basis for the emergence of life. These problems are necessarily closer to physics and systems chemistry than any other transition, and we approach them using phase transitions and bifurcations as central organizing concepts. Symmetry breaking and percolation provide the mathematical framework for understanding key steps in the origins of life, from molecular chirality to the first self-replicating chemical networks.

We believe that studying these synthetic transitions not only helps us understand the underlying laws that predate the rise of major innovations, but also provides an arena where other issues — such as how difficult certain transitions are to occur, or whether entirely new transitions might exist — can be rigorously explored.