Bacterial Evolution and Involution

Fernando Baquero, Kenneth Timmis

In biology, the concept of evolution is often linked to an increase in directional complexity driven by particular selective landscapes. In contrast, involution is understood as the loss of adaptive gains achieved through evolution, leading to de-adaptation to the environment and eventually to extinction. However, the microecological heterogeneity of spaces occupied by bacteria necessarily makes evolution a diversifying force, gradually producing more specialized variants. The fit between the environment and adapted bacteria results in the loss of function of genes not required for adaptation, which become a burden on bacterial replication and initiate reductive genetic evolution, which can be considered an involution. Therefore, evolution produces involution. At this stage, involutionary entities start to collaborate with each other, creating novel entities at a higher hierarchical level, as may occur with the microbiome. Alternatively, the involutionary entity exploits higher organisms, such as eukaryotic cells, at the expense of losing its bacterial ontology and being converted into organelles. Therefore, involution produces evolution. Involutory intermediates may give rise to novel evolutionary trajectories. These trade-offs can be studied in experimental evolutionary models.