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New Evolutionary Research Disproves Living Missing Link Theories

Genetic research proves worm has evolved to be less sophisticated than its ancestors

Evolution is not a steady march towards ever more sophisticated beings and therefore the search for the living "missing links" is pointless, according to findings published by a team of researchers led by Dr. Hervé Philippe of the Université de Montréal's Department of Biochemistry.

"Aristotle was the first to classify organisms – from the least to the most sophisticated. Darwin's theory of evolution continued this idea, with the concept of a hierarchy of evolution. This way of thinking has led researchers and skeptics alike to look for less sophisticated ancestors in order to prove or disprove evolution," Philippe explained. "What we now know is that evolution does not happen in a single direction – when people talk about a missing link, they're generally excluding the possibility of more sophisticated ancestors."

The researchers compared the genomes of two kinds of marine worms with simple morphology – Xenoturbellida and Acoelomorpha – with those of other animals. They demonstrated that their previous position at the base of the bilateral symmetry animal group – that includes insects, mollusks and vertebrates – was inaccurate. "Instead, we determined that Xenoturbellida and Acoelomorpha are closely related to the complex deuterostomes, which is a major lineage containing sea urchins, humans and sharks," Philippe said. "I've put them in that order intentionally because it seems strange, which demonstrates our tendency to always put organisms in order of complexity." The findings mean that the worms had evolved from a more sophisticated ancestor through major simplifications.

"We did already know that most parasitic organisms had evolved to be less sophisticated than their ancestors – they lost certain abilities that they no longer needed. The independently living Xenoturbellida and Acoelomorpha do not fall in this category," Philippe said. The research is a striking example for the important role of secondary simplification in evolution and is part of 20 year project that is nearing completion. The findings were published in Nature on February 10, 2011.

Une récente étude sur l'évolution réfute les théories sur le chaînon manquant vivant

La recherche génétique prouve que certains vers marins ont évolué vers une complexité réduite, comparativement à celle de leurs ancêtres

MONTRÉAL, le 10 février 2011 – Selon des découvertes publiées par une équipe de chercheurs dirigée par le professeur Hervé Philippe, du Département de biochimie de l'Université de Montréal, l'évolution n'est pas une marche constante vers des êtres de plus en plus sophistiqués et, par conséquent, la quête de chaînons manquants parmi les espèces vivant aujoud'hui n'est pas pertinente. « Aristote a été le premier à classifier les organismes, du plus simple au plus complexe. La théorie de l'évolution de Darwin a étendu cette notion, ajoutant l'idée d'une classification hiérarchique des organismes. Cette façon de penser a conduit des scientifiques – et des sceptiques – à chercher des ancêtres moins complexes, de manière à prouver ou réfuter l'évolution », a expliqué monsieur Philippe. « Ce que nous savons maintenant, c'est que l'évolution ne se produit pas dans une seule direction. Quand les gens parlent d'un chaînon manquant, ils mettent généralement de côté la possibilité d'ancêtres plus complexes que les espèces actuelles. »

L'équipe internationale de chercheurs a comparé les génomes de deux espèces de vers marins présentant une morphologie simple, les Xenoturbellida et les Acoelomorpha, avec ceux d'autres animaux. Ils ont démontré que leur ancienne position à la base du groupe des animaux à symétrie bilatérale – comprenant insectes, mollusques et vertébrés – n'était pas appropriée. « À la place, nous avons déterminé que les Xenoturbellida et les Acoelomorpha font partie des deutérostomiens, une sous-division importante réunissant les oursins, les humains et les requins », a ajouté le professeur Philippe. « L'ordre de ces trois groupes est intentionnel, cela semble étrange, mais démontre notre tendance à toujours ranger les organismes par ordre de complexité. » Cette découverte signifie que l'évolution de ces vers marins, à partir d'un ancêtre plus complexe, s'est déroulée à travers d'importantes simplifications.

« Nous savions déjà que la plupart des organismes parasitaires ont évolué pour devenir moins complexes que leurs ancêtres; ils ont perdu certaines aptitudes dont ils n'ont plus besoin. Les Xenoturbellida et les Acoelomorpha, qui vivent de façon indépendante, ne font pas partie de cette catégorie », a déclaré Hervé Philippe. Réalisée dans le cadre d'un projet s'échelonnant sur près de 20 ans et touchant à sa fin, l'étude est un exemple frappant du rôle important de la simplification secondaire dans l'évolution. Les résultats ont été publiés le 10 février 2011, dans Nature.

William Raillant-Clark | Newswise Science News
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