Thursday, January 22, 2009

A Paradigm Shift In Evolutionnary Theory ?

The modern interpretation of evolutionnary theory, known as Neodarwinsim, has put too much emphasis on some aspects of the theory: Competition, Adaptation, and Genes. Those themes became popular among evolutionnary scientists and eclipsed many others. The great evolutionnary biologist Ernst Mayr stated that there are four major components to the theory:

Common origin
Evolution by Random variations

The last two processes are thought to result in the survival of the fittiest.

Only the common origin stands outside scientific scrutiny today. And while random variations are not disputed, their role in evolution has been questioned by, among others, Lynn Margulis who advocated symbiogenesis, instead of random genetic variations, as the main factor in evolution. Selection and Adaptation, which are interdependant in Neodarwinism, leading to the survival of the fittiest, were seen by the late evolutionnary biologist Stephen Jay Gould as anthropomorphic concepts borrowed by Darwin from the social sciences of his time. Gould used to stress at the beginning of many of his talks that selection by adaptation and survival of the fittiest didn't work well for Adam Smith but worked for Darwin. As a matter of fact, Darwin, in a first draft of the theory, didn't mention fitness and adaptation. For a very long time, Darwin was reluctant to publish his book 'The origin of species by means of natural selection', he needed to fill some gaps in the explanation, and these gaps came from the social sciences at a time when Darwin was pressed by his friends to go ahead and publish his theory unless Wallace, who had the same intuition about evolution, was going to publish before him.
Gould found that the modern interpretation of two apsects of the theory of evolution, selection and adaptation, by emphasising the role of random variation of the gene to suit the environment, and later to suit the gene itself, according to Dawkins' 'selfish gene', has a teleological feature. This is a negative statement since science and nature have no goals, no intention. Only humans, and God, have purpose. For Gould, there is no goal in Nature, not even adaptation, there are only chance, accident, and contingency.

At the heart of this modern interpretation of Darwin's theory there is an old definition to a concept not well understood, the concept of Species. For a very long time, the concept of Species was understood from the standpoint of interbreeding: animals fronm the same Species are those who can interbreed. There were some recognised minor exceptions, but they were still exceptions. However, a new study is going to shake this definition and with it probably the edifice of the modern interpretation. This new study is not the only one to question the old definition of Species. Lynn Margulis, who studied bacteria, showed that small organisms, like bacteria, swap their genes very frequently. This process is the last step in symbiotic life, when symbiosis between two Species is long enough to change the phenotype of both organisms when they are not in symbiosis,and when it leads to some mix of genes in the new organism. Indeed, says Margulis, because of frequent gene swap in bacteria, one can affirm that there are no Species in bacteria. Margulis was one of the few evolutionnary biologists working at the margins of the Neodarwinist paradigm, claiming that Neodarwinism neglected data from small organisms and from symbiotic life, in the interpretation, and concerned itself only with big animals and competition. For her, small organisms, and symbiogenesis tell us a different story on Evolution. A story of cooperation instead of competition.

Indeed, the new study suggests that:
As more and more genes were sequenced, it became clear that the patterns of relatedness could only be explained if bacteria and archaea were routinely swapping genetic material with other species - often across huge taxonomic distances - in a process called horizontal gene transfer (HGT)...As it became clear that HGT was a major factor, biologists started to realise the implications for the tree concept. As early as 1993, some were proposing that for bacteria and archaea the tree of life was more like a web. In 1999, Doolittle made the provocative claim that "the history of life cannot properly be represented as a tree" (Science, vol 284, p 2124). "The tree of life is not something that exists in nature, it's a way that humans classify nature," he says

Horizontal Gene Transfer (HGT) is opposed to the classical vision of Gene Transfer, which is the vertical one in the Tree of life of Darwin, the vertical descent of Species.
Interbreeding is swapping genes. And swapping genes between unicellular animals, even unicellular eukaryotes, when it happens in multicellular and big animals is called hybridisation. Most scientists concerned with big animals think that hybridisation is an exception. But that's not the fact. The fact is that hybridisation concerns more than 10% of multicellular eukaryotes (i.e. organisms). And genetic studies of big animals are revealing that HGT is happening in big animals also as ''ever more incongruous bits of DNA are turning up in multicellular genomes''.

Last year, for example, a team at the University of Texas at Arlington found a peculiar chunk of DNA in the genomes of eight animals - the mouse, rat, bushbaby, little brown bat, tenrec, opossum, anole lizard and African clawed frog - but not in 25 others, including humans, elephants, chickens and fish. This patchy distribution suggests that the sequence must have entered each genome independently by horizontal transfer (Proceedings of the National Academy of Sciences, vol 105, p 17023).

And what exactly does this mean for the tree of life of Darwin and for the Theory of Evolution ?

...downgrading the tree of life doesn't mean that the theory of evolution is wrong - just that evolution is not as tidy as we would like to believe. Some evolutionary relationships are tree-like; many others are not.
That's one reassuring point of view.

And the one that is not reassuring:
"Our standard model of evolution is under enormous pressure. We're clearly going to see evolution as much more about mergers and collaboration than change within isolated lineages."
Rose goes even further. "The tree of life is being politely buried, we all know that," he says. "What's less accepted is that our whole fundamental view of biology needs to change." Biology is vastly more complex than we thought, he says, and facing up to this complexity will be as scary as the conceptual upheavals physicists had to take on board in the early 20th century.

If we reconsider Mayr's components for Darwin's theory (listed above), we may end up with a completely different picture:

Common origin
Evolution, not so much by random variations, but by Horizontal Gene Transfer (HGT), or interspecies breeding, or symbiogenesis
Selection and adaptation by survival of the fittiest are replaced by cooperation.

Exit Richard Dawkins, Daniel Dennett, Steven Pinker, Jean-Pierre Changeux, and all those ultradarwinists that stressed vertical descent and competition. Enter Stephen Jay Gould, Lynn Margulis, and a new era of cooperative and messy Biology, a solidary world. The change of paradigm is certain. However, one might ask at the beginning of this economic and ecological crises if the new paradigm is not, yet again, influenced by what is going on in our human world...

New Scientist, 21 January, 2009. 'Why Darwin was wrong about the tree of life'

UPDATE 1: February, 10th, 09: Darwinism must die so that Evolution may live.
UPDATE 2: February, 10th, 09: The old paradigm is resisting.

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