Volume 375, Issue 9709, 9 January 2010-15 January 2010, Pages 104-105
Comment
The post-Darwinist rhizome of life
Didier Raoult
URMITE CNRS-IRD UMR 6236, Faculté de Médecine, Unité des Rickettsies,
13385 Marseille, France
Available online 8 January 2010.
In 2009, with the 200th anniversary of Darwin's birthday, the concept of Darwinism became so popular that it was celebrated in most biological journals. However, the Darwinist theory of evolution is associated with the scientific knowledge and outdated beliefs of the 19th century. The theory is characterised by a description of life as a tree in which all living organisms are thought to have a single ancestor and where each node represents a common ancestor (Darwin's tree).1 Such a theory was characteristic of the vision comprising the hierarchy and dichotomy of the 19th century. The demonstration of species segregation with no crossing over was instrumental for later racist theories based on Darwin's work, called social Darwinism. The structure of our current knowledge base has changed substantially. The internet has been developed since 1989 and, according to theories proposed by post-modernist philosophers,2 the giant Wikipedia encyclopaedia is more akin to a rhizome than a tree, the latter being more representative of the French encyclopaedia from the 18th century.
In the 21st century, the genomic revolution has brought about an important change in the way we think about life, which has forced us to reconsider the way we describe evolution.[3] and [4] Genomic data have gradually accumulated and show that there were multiple original sources of the genetic information of living organisms, with inheritance occurring not only vertically but also laterally.5 Such lateral gene transfer, initially observed only in bacteria, was quickly identified in all living organisms. For example, the human genome is a mosaic of genes with eukaryotic, bacterial (in the mitochondria and the nucleus), and viral origins. Bacteria have genes that originated from eukaryotic, archaeal, and viral organisms. Giant viruses also have chimeric genomes of different origins.6 The number of recent and massive gene-transfer events has been exemplified by the recent discovery of the integration of practically the entire Wolbachia bacterial genome into its eukaryotic host.7 Finally, many genes have been found to be purely selfish and multiply in different organisms.4
Thus we cannot currently identify a single common ancestor for the gene repertoire of any organism. Comparative genome analysis shows not only a substantial level of plasticity in the gene repertoire, but also provides evidence that nearly all genes, including ribosomal genes, have been exchanged or recombined at some point in time. Overall, it is now thought that there are no two genes that have a similar history along the phylogenic tree.
Moreover, there are some genes that do not have a single history, due to the occurrence of intragenic recombinations. Therefore the representation of the evolutionary pathway as a tree leading to a single common ancestor on the basis of the analysis of one or more genes provides an incorrect representation of the stability and hierarchy of evolution. Finally, genome analyses have revealed that a very high proportion of genes are likely to be newly created through gene fusion, degradation, or other events, and that some genes are only found in one organism (named ORFans).8 These genes do not belong to any phylogenic tree and represent new genetic creations.
A post-Darwinist concept of the living species can be proposed, to integrate the theories of multiplicity and de-novo creation. In accordance with the theory on the evolution of human societies proposed by Deleuze and Guattari,2 I believe that the evolution of species looks much more like a rhizome (or a mycelium) (figure). Consequently, this view of evolution resembles a clump of roots that considers the occurrence of multiplicities. Emerging species grow from the rhizome with gene repertoires of various origins that will allow, under favourable environmental conditions, the multiplication and perpetuation of this species. As such, potential new species and new genes are continuously appearing. The success of the species and thus their overall evolution depend mainly on the fitness of the species within their particular environmental conditions at a particular time. The disappearance of a species is not necessarily associated with the disappearance of the genes of its repertoire and each gene can continue along its own history.4 I suggest we respect the revolutionary mind of Darwin and allow the theory of evolution itself to evolve from a tree to a rhizome.
Figure. Rhizome of life
Roots of genes of living species are shown according to current classification of organisms: eukaryotes (red), bacteria (blue), viruses (green), archaea (yellow). In purple are genes without identified origin (ORFans). At the surface, in form of mushrooms, are the current species, containing mixture of genes of different origin. Colour of mushroom envelope is determined by origin of core genome of the species.
View Within Article
I thank Christelle Forzale for help with the figure. I declare that I have no conflicts of interest.
References
1 C Darwin, On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life, John Murray, London (1859).
2 G Deleuze and F Guattari, Rhizome: introduction, Éd de Minuit, Paris, France (1976).
3 EV Koonin, Darwinian evolution in the light of genomics, Nucleic Acids Res 37 (2009), pp. 1011–1034. View Record in Scopus | Cited By in Scopus (15)
4 R Dawkins, The selfish gene (3rd edn.), Oxford University Press, Oxford, UK (2006).
5 WF Doolittle and E Bapteste, Pattern pluralism and the tree of life hypothesis, Proc Natl Acad Sci USA 104 (2007), pp. 2043–2049. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (84)
6 D Raoult and P Forterre, Redefining viruses: lessons from Mimivirus, Nat Rev Microbiol 6 (2008), pp. 315–319. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (27)
7 E Callaway, Genomes within genomes, Nature 449 (2007), p. 6. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (1)
8 CM Fraser, JA Eisen and SL Salzberg, Microbial genome sequencing, Nature 406 (2000), pp. 799–803. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (75)
The Lancet
Volume 375, Issue 9709, 9 January 2010-15 January 2010, Pages 104-105
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NOTA DESTE BLOGGER:
O conceito de Árvore da Vida qua Darwin, kaput! Otras cositas mais no artigo que devem mexer na crença dogmática da onipresente, onipotente, e onisciente seleção natural. Gente, o oba-oba, as louvaminhices, e beija-mão e beija-pé de Darwin ainda não acabaram (dia 14 de fevereiro é aniversário do homem que teve a maior ideia que toda a humanidade já teve), e a turma dissidente já está tirando umas casquinhas do nosso guru de Down.
Os ídolos foram feitos para destruição. Onde foi mesmo que eu li isso? Darwin-ídolo será destruído.
Quem viver, verá... Quem será o Finéias de Darwin no Brasil???
O conceito de Árvore da Vida qua Darwin, kaput! Otras cositas mais no artigo que devem mexer na crença dogmática da onipresente, onipotente, e onisciente seleção natural. Gente, o oba-oba, as louvaminhices, e beija-mão e beija-pé de Darwin ainda não acabaram (dia 14 de fevereiro é aniversário do homem que teve a maior ideia que toda a humanidade já teve), e a turma dissidente já está tirando umas casquinhas do nosso guru de Down.
Os ídolos foram feitos para destruição. Onde foi mesmo que eu li isso? Darwin-ídolo será destruído.
Quem viver, verá... Quem será o Finéias de Darwin no Brasil???
