The Biological Big Bang - EV Koonin



The article Biological Big Bang (BBB) model is a hypothesis proposed by Eugene Koonin to explain the major transitions in evolution. These transitions are periods of rapid evolution that lead to the emergence of new levels of biological complexity, such as the origin of cells, the origin of multicellularity, and the origin of complex animals.

The BBB model posits that these transitions are characterized by two phases: an inflationary phase and a consolidation phase. The inflationary phase is a period of rapid genetic innovation, during which there is extensive exchange of genetic information between different lineages. This exchange can occur through processes such as horizontal gene transfer, recombination, and fusion. The result of this phase is a vast diversity of new forms, from which the major classes of entities at the new level of complexity emerge.

The consolidation phase is a period of slower evolution, during which the new forms are tested and refined.

The BBB model has been applied to a number of major transitions in evolution, including:

  • The origin of cells

  • The origin of multicellularity

  • The origin of complex animals

  • The origin of eukaryotic cells

  • The origin of the RNA world

The BBB model has been met with some criticism, but it has also been praised for its ability to explain the rapid and dramatic changes that occur during major transitions in evolution.

Here are some of the key features of the BBB model:

  • It is a two-phase model, with an inflationary phase and a consolidation phase.

  • The inflationary phase is characterized by rapid genetic innovation and extensive exchange of genetic information.

  • The consolidation phase is characterized by the gradual refinement of new forms.

  • The BBB model has been applied to a number of major transitions in evolution.

The Biological Big Bang (BBB) model is a radical departure from the neo-Darwinian paradigm. In neo-Darwinism, evolution is seen as a gradual process of genetic change driven by natural selection. The BBB model, on the other hand, proposes that major evolutionary transitions, such as the origin of cells, multicellularity, and sexual reproduction, occurred in sudden bursts of innovation.

Koonin argues that these bursts of innovation were made possible by the emergence of new genetic and epigenetic mechanisms that allowed for the rapid exchange of genetic information. These mechanisms included the evolution of mobile genetic elements, such as transposons and retroviruses, and the development of new ways of regulating gene expression.

The BBB model has had a significant impact on the way we think about evolution. It has forced us to reconsider the role of chance and contingency in evolution, and it has opened up new avenues of research into the mechanisms that drive major evolutionary transitions.

Here are some of the key differences between the BBB model and neo-Darwinism:

  • The BBB model emphasizes the importance of sudden bursts of innovation, while neo-Darwinism emphasizes the gradual accumulation of small changes.

  • The BBB model sees major evolutionary transitions as being driven by the emergence of new genetic and epigenetic mechanisms, while neo-Darwinism sees them as being driven by natural selection.

  • The BBB model is more speculative than neo-Darwinism, as it relies on mechanisms that have not yet been fully characterized.

Overall, the BBB model is a radical departure from the neo-Darwinian paradigm. It has the potential to revolutionize our understanding of evolution, but it also needs to be further tested and refined.

Article snippets:


Major transitions in biological evolution show the same pattern of sudden emergence of diverse forms at a new level of complexity

The relationships between major groups within an emergent new class of biological entities are hard to decipher and do not seem to fit the tree pattern that, following Darwin's original proposal, remains the dominant description of biological evolution

The cases in point include the origin of complex RNA molecules and protein folds; major groups of viruses; archaea and bacteria, and the principal lineages within each of these prokaryotic domains; eukaryotic supergroups; and animal phyla

In each of these pivotal nexuses in life's history, the principal "types" seem to appear rapidly and fully equipped with the signature features of the respective new level of biological organization

No intermediate "grades" or intermediate forms between different types are detectable.

The first, inflationary phase is characterized by extremely rapid evolution driven by various processes of genetic information exchange, such as horizontal gene transfer, recombination, fusion, fission, and spread of mobile elements.

These processes give rise to a vast diversity of forms from which the main classes of entities at the new level of complexity emerge independently,

It is proposed that bacterial and archaeal phyla emerged independently from two distinct populations of primordial cells that, originally, possessed leaky membranes, which made the cells prone to rampant gene exchange; and that the eukaryotic supergroups emerged through distinct, secondary endosymbiotic events

Origin of viruses

there is no evidence of a common ancestry for all viruses

Origin of cells

This severely complicates the reconstruction of a cellular ancestor of archaea and bacteria and suggests alternative solutions

Origin of the major branches (phyla) of bacteria and archaea

The division of the archaea into two branches, euryarchaeota and crenarchaeota is better established but even this split is not necessarily reproduced in trees, and further divisions in the archaeal domain remain murky

Origin of the major branches (supergroups) of eukaryotes

relationship between them remaining unresolved

Origin of the animal phyla

The Cambrian explosion in animal evolution during which all the diverse body plans appear to have emerged almost in a geological instant is a highly publicized enigma


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