The Tree of One Percent

"As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications." - Darwin's tree of Life

The article "The Tree of One Percent" by Tal Dagan and William Martin discusses the limitations of the tree of life model for understanding microbial evolution. The tree of life is a branching diagram that depicts the evolutionary relationships between all living things. It is based on the assumption that all life evolved from a common ancestor through a series of bifurcations, or lineage splittings.

However, lateral (Horizontal) gene transfer (LGT aka HGT) is a common process in microbial evolution. LGT is the horizontal transfer of genes between unrelated organisms. It can occur through a variety of mechanisms, such as conjugation, transformation, and transduction. LGT can have a significant impact on microbial evolution, as it allows organisms to acquire new genes and traits from other organisms.

NeoDarwinism was based on Gregory Mendel's vertical (sexual) transmission.

Dagan and Martin argue that LGT is so common in microbial evolution that it makes it difficult to construct a tree of life that accurately reflects the evolutionary relationships between all microbes. They estimate that only 0.1% to 1% of each microbial genome fits the tree of life model. This suggests that the vast majority of microbial genes have been transferred laterally between organisms at some point in their evolutionary history.

Dagan and Martin propose a number of alternatives to the tree of life model for understanding microbial evolution. One alternative is the symbiotic tree model. This model proposes that the ancestor of eukaryotes originated by the endosymbiosis of one prokaryote in another prokaryote host. Endosymbiosis is a process in which one organism comes to live inside another organism. The different groups of eukaryotes arose by subsequent separate endosymbiotic events involving various prokaryotes.

Dagan and Martin also propose a number of other models for understanding microbial evolution, such as the network model and the mosaic model. 

These models are more complex than the tree of life model, but they are better able to account for the complex evolutionary processes that occur in microbes.

The article "The Tree of One Percent" is an important contribution to the debate about how to understand microbial evolution. It highlights the limitations of the tree of life model and proposes a number of alternative models that are better able to account for the complex evolutionary processes that occur in microbes.

The article provides is a discussion of the role of lateral gene transfer (LGT) and endosymbiosis in microbial evolution, and their implications for the concept of a tree of life.

What are LGT and endosymbiosis?

  • LGT is the process by which genetic material is transferred between organisms that are not parent and offspring. This can happen in a variety of ways, such as through conjugation, transformation, and transduction. LGT is very common among prokaryotes, and it is thought to play a major role in their evolution.

  • Endosymbiosis is the process by which one organism takes up residence inside another organism. This can be a mutually beneficial relationship, or the endosymbiont can become parasitic. Endosymbiosis is thought to have played a major role in the evolution of eukaryotes, as the mitochondria and chloroplasts are thought to have originated as endosymbiotic bacteria.

How do LGT and endosymbiosis affect the tree of life?

LGT and endosymbiosis can both make it difficult to reconstruct the evolutionary relationships between organisms using traditional phylogenetic methods. This is because LGT and endosymbiosis can lead to the transfer of genes between organisms that are not closely related.

As a result, some biologists have argued that the concept of a tree of life is not appropriate for describing microbial evolution. They argue that the evolutionary relationships between microbes are more complex and interconnected than can be represented by a single tree.

What is the "tree of one percent"?

The "tree of one percent" is a term used to describe the tree of life that is constructed using only the genes that are 

The article you have provided is a discussion of the role of lateral gene transfer (LGT) and endosymbiosis in microbial evolution, and their implications for the concept of a tree of life.

What are LGT and endosymbiosis?

  • LGT is the process by which genetic material is transferred between organisms that are not parent and offspring. This can happen in a variety of ways, such as through conjugation, transformation, and transduction. LGT is very common among prokaryotes, and it is thought to play a major role in their evolution.

  • Endosymbiosis is the process by which one organism takes up residence inside another organism. This can be a mutually beneficial relationship, or the endosymbiont can become parasitic. Endosymbiosis is thought to have played a major role in the evolution of eukaryotes, as the mitochondria and chloroplasts are thought to have originated as endosymbiotic bacteria.

How do LGT and endosymbiosis affect the tree of life?

LGT and endosymbiosis can both make it difficult to reconstruct the evolutionary relationships between organisms using traditional phylogenetic methods. This is because LGT and endosymbiosis can lead to the transfer of genes between organisms that are not closely related.

As a result, some biologists have argued that the concept of a tree of life is not appropriate for describing microbial evolution. They argue that the evolutionary relationships between microbes are more complex and interconnected than can be represented by a single tree.

What is the "tree of one percent"?

The "tree of one percent" is a term used to describe the tree of life that is constructed using only the genes that are universally distributed among all genomes. This tree is thought to represent the core evolutionary relationships between organisms, but it is very incomplete, as it excludes all of the genes that have been transferred by LGT or endosymbiosis.

What are the implications of the "tree of one percent"?

The discovery of the "tree of one percent" suggests that LGT and endosymbiosis have played a major role in the evolution of all life. It also suggests that the traditional concept of a tree of life is not sufficient to describe microbial evolution.

Conclusion

The article concludes by arguing that biologists should abandon the tree of life as a working hypothesis for microbial evolution. It argues that the evolutionary relationships between microbes are more complex and interconnected than can be represented by a single tree.

Ultimately, biologists need to be open-minded about the nonDarwinian possibility that the evolutionary relationships between microbes may not be able to be represented by a single tree or network model. It is possible that the evolutionary relationships between microbes are so complex and interconnected that they cannot be fully described by any single model.

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