Figure 2

Biological Big Bangs and the emerging pattern of tree-like evolution: transitions between rapid and slow phases of evolution in the history of life. The transition between the rapid, inflationary, and slow, tree-like, phases of evolution is shown by the red line and denoted BBB. The similarity to the depiction of Big Bang events in the evolution of the multiverse in Fig. 3 is deliberate. I. The pre-cellular BBBs. The squiggles of different colors denote genetic elements in the primordial gene pool, and arrows denote recombination/fusion processes. The emerging trees are those of individual genes and virus-like agents. The emergence of the proto-archaeal (A) and proto-bacterial (B) cells is shown as well. II. Origin of the major bacterial lineages. The rounded rectangles show proto-bacterial cells with leaky membranes (broken lines). The arrows denote extensive horizontal gene transfer. The colored shapes denote emerging bacterial lineages (trees) with tighter membranes (solid lines). A similar schematic for the origin of archaeal lineages is not shown. III. Origin of the eukaryotic supergroups. The irregular shapes show proto-eukaryotic cells that already harbored mitochondria derived from α-proteobacteria (dark green shapes inside – shown to derive from one of the bacterial trees supposed to correspond to the proteobacterial lineage) and have evolved nuclei (red spheroids, so colored to emphasize the archaeal connection). The archaeal ancestry of eukaryotes is denoted by a broken arrow (the intermediate, inflationary phase is omitted). Arrows show secondary symbioses with other bacteria or primitive eukaryotes (colored shapes) that are postulated to give rise to the eukaryotic supergroups (trees).