There is no firm theoretical reason to expect evolutionary lineages to increase in complexity with time, and no empirical evidence that they do so. Nevertheless, eukaryotic cells are more complex than prokaryotic ones, animals and plants are more complex than protists, and so on. This increase in complexity may have been achieved as a result of a series of major evolutionary transitions. These involved changes in the way information is stored and transmitted. The impressive body of work on the major evolutionary transitions (initiated by Maynard Smith and Szathmáry) in the last 25 years has helped improve the theory considerably, although a 2D account (evolution of informational systems and transitions in individuality) remains. Significant advances include the concept of fraternal and egalitarian transitions (lower-level units like and unlike, respectively). Multilevel selection, first without, then with, the collectives in focus is an important explanatory mechanism. Transitions are decomposed into phases of origin, maintenance, and transformation (i.e., further evolution) of the higher level units, which helps reduce the number of transitions in the revised list by two so that it is less top-heavy. After the transition, units show strong cooperation and very limited realized conflict. Some of the transitions can be recursive (e.g., plastids, multicellularity) or limited (transitions that share the usual features of major transitions without a massive phylogenetic impact, such as the micro- and macronuclei in ciliates). During transitions, new units of reproduction emerge, and establishment of such units requires high fidelity of reproduction (as opposed to mere replication).
We at ETI continue to focus on the following issues: transition from chemistry to biology (molecular replicators and spatial structure, early metabolism and chromosome evolution), eukaryotic origins (especially of mitochondria), general replicator theory (from molecules to memes), evolutionary origin and dynamics of information-handling subsystems (immune and nervous systems), eco-evolutionary emergence of language (in hominins and robots), language as a biological system.