Perspectives on the Phylogenetic Tree

Ring of Life Models

Others have proposed abandoning any tree-like model of phylogeny in favor of a ring structure, the so-called “ring of life” (Figure). This is a phylogenetic model where all three domains of life evolved from a pool of primitive prokaryotes. Lake, again using the conditioned reconstruction algorithm, proposes a ring-like model in which species of all three domains—Archaea, Bacteria, and Eukarya—evolved from a single pool of gene-swapping prokaryotes. His laboratory proposes that this structure is the best fit for data from extensive DNA analyses performed in his laboratory, and that the ring model is the only one that adequately takes HGT and genomic fusion into account. However, other phylogeneticists remain highly skeptical of this model.

Illustration shows a ring with the words “pool of primitive prokaryotes” in the middle. Three arrows point outward from the ring, pointing at the three domains, Bacteria, Archaea, and Eukarya, indicating that all three domains arose from a common pool of prokaryotes.
According to the “ring of life” phylogenetic model, the three domains of life evolved from a pool of primitive prokaryotes.

In summary, we must modify Darwin's “tree of life” model to include HGT. Does this mean abandoning the tree model completely? Even Lake argues that scientists should attempt to modify the tree model to allow it to accurately fit his data, and only the inability to do so will sway people toward his ring proposal.

This doesn’t mean a tree, web, or a ring will correlate completely to an accurate description of phylogenetic relationships of life. A consequence of the new thinking about phylogenetic models is the idea that Darwin’s original phylogenetic tree concept is too simple, but made sense based on what scientists knew at the time. However, the search for a more useful model moves on: each model serves as hypotheses to test with the possibility of developing new models. This is how science advances. Researchers use these models as visualizations to help construct hypothetical evolutionary relationships and understand the massive amount of data that requires analysis.