• L’orgasme féminin : un vestige de l’évolution

    Par trichard le 22 Octobre 2007 à 22:57

    M. Philippe Ciofi est neuroanatomiste à l'Institut François Magendie, INSERM U378, à Bordeaux.

    Pourquoi certaines femmes ont-elles des orgasmes, et d'autres non ? Dans un livre récent, la biologiste Elisabeth Lloyd défend une thèse controversée : comme les femmes n'ont pas besoin d'éprouver du plaisir pour avoir des enfants, cette capacité, qui n'est pas indispensable à la survie de l'espèce, se serait raréfiée chez elles.

    Extrait :
    Pourquoi les hommes et les femmes sont-ils inégaux face à l'orgasme ? Tous les hommes, peu ou prou, connaissent cette sensation de plaisir culminant, alors  que certaines femmes n'y goûtent jamais. Pourquoi la nature aurait-elle distribué les cartes de façon si inégale ?
    La question est moins anodine qu'il n'y paraît. La fonction de reproduction occupe une place centrale dans l'évolution des espèces, dont elle est à la fois le substrat et le moteur. Le substrat, car la vision classique de Darwin propose que les individus les plus aptes à se reproduire ont une plus grande descendance, descendance sur laquelle s'exerce la sélection naturelle. Le moteur aussi, car, pour être transmises de parents à enfants, les mutations génétiques aléatoires, qui introduisent les légères variations interindividuelles porteuses d'avantages adaptatifs, doivent toucher les ovules et les spermatozoïdes. [...]

    http://www.pourlascience.com/index.php?ids=TKbFZtMQVEmvZnXonclh&Menu=Cp&Action=2&idn3=550# 


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  • quelques empreintes fossiles de 315 Ma

    Par trichard le 18 Octobre 2007 à 21:15

    A feast of fossil footprints - October 17, 2007

    fossilfootprints.JPG
    Reptiles have been around a little longer than we thought, a stunning fossil find reveals. Footprints found in New Brunswick, Canada push back the date of the first reptiles, which evolved around 315 million years ago. “The evolution of reptiles was one of the most important events in the whole history of life,” said the fossil's finder Dr Howard Falcon-Lang, a paelontologist at the University of Bristol (BBC, Times).

    Previously the oldest evidence of reptiles was fossils found in 1859. The new footprints were found in the same region as the previous fossils but about a kilometre lower in the rock strata, meaning they are between one and three million years older. The findings are reported in the Journal of the Geological Society. “There were only a few species capable of making prints like this around at the time so we came up with a short-list of suspects. However, the prints showed that the hands had five fingers and scales, sure evidence they were made by reptiles and not amphibians,” said one of Falcon-Lang's co-authors on the paper Mike Benton (press release).

    In a strangely similar story researchers working in Germany are claiming to have found the oldest footprints positively identified, after fossils of two ‘reptile-like' animals from 290 million years ago were matched to fossil tracks (Live Science). Their results are published in the Journal of Vertebrate Paleontology.

    Image: Howard Falcon-Lang

    Posted by Daniel Cressey on October 17, 2007

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  • Néandertal aimait les fruits de mer

    Par trichard le 18 Octobre 2007 à 21:11

    An early taste for seafood - October 18, 2007

    It looks like Homo sapiens headed to the beach and engaged in ‘modern behaviours' such as eating seafood, making delicate knives, and grinding up shells to make paints some 40,000 years earlier than previously known (there's a host of stories on this today, see for example the New York Times and BBC).

    The earliest previous evidence for human use of marine resources was dated to around 125,000 years ago (followed by evidence of Neanderthals cooking shellfish in Italy about 110,000 years ago). Now Curtis Marean and colleagues report in Nature findings from a sea cave in South Africa suggesting people were living on the coast there around 164,000 years ago (Nature paper subscription needed; press release). The authors propose these coast-dwellers may have been driven to seafood to survive a cool, dry spell that turned most of Africa to desert.

    I have always thought that coastal living was one of the easier ways of life – with plentiful food, water, and a more moderate climate – so had assumed that early peoples would have flocked to the shore. But apparently the prevailing wisdom is that the earliest modern humans (some 150,000 to 200,000 years ago) preferred hunting inland game. “Shellfish was one of the last additions to the human diet before domesticated plants and animals were introduced,” team leader Marean (sadly pronounced 'mar-e-an' rather than ‘marine') told the NY Times.

    The African press doesn't seem to have done much with the story, though Reuters Africa reports: For early humans, a beach party and clam bake in S.Africa.

    Posted by Nicola Jones on October 18, 2007

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  • Empreinte de Tyrannosaurus rex : 76 cm

    Par trichard le 11 Octobre 2007 à 21:33

    T. Rex reigned in Hell Valley - October 10, 2007 / http://blogs.nature.com/news/thegreatbeyond/2007/10/t_rex_reigned_in_hell_valley.html

    t-rexalamy.jpgAn ultra-rare T. Rex footprint may have been found in the Badlands of Montana. Phil Manning, from the Manchester Museum, University of Manchester, claims a metre-square track he found in rocks called the Hell Creek Formation was left by that most iconic of dinosaurs around 65 million years ago. “It could only be made by one of the two species known from Hell Creek - either the Nanotyrannus or its bigger relative, Tyrannosaurus rex. The size of the footprint at 76cm in length suggests it is more likely to be the latter,” he told a BBC documentary.

    There is one previous claimed T. Rex footprint, discovered in New Mexico in 1983 and published 11 years later (see USGS). A number of news sources however are reporting this as the first ever found (PA, Daily Mail). A report on the fossil has apparently been submitted for peer review. Whether or not this is truly a T. Rex footprint will probably never be known. As Manning says: “Unless you come across an animal dead in its tracks you can't say for definite what left them.”

    A reportage piece on the hunt for the footprint is already up on the BBC website, and there is a video clip of the footprint on YouTube.

    Image: Alamy


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  • Suzhousaurus megatherioides

    Par trichard le 11 Octobre 2007 à 21:31

    Dinosaur of the day - October 09, 2007 / http://blogs.nature.com/news/thegreatbeyond/2007/10/dinosaur_of_the_day.html

    suzy.bmpThose who enjoyed Nature's recent feature on the Walking With Dinosaurs live experience currently touring America may be interested to know that a team including the palaeontologist featured in that article, Ken Lacovara of Drexel University, has just announced the discovery of a fearsome looking but apparently plant eating new dinosaur Suzhousaurus megatherioides. The team was led by Dr Hai-Lu You of the Chinese Academy of Geological Science and the research is published in Acta Geologica Sinica. In a press release, Lacovara describes the therizinosaurs, of which this is one, as being "characterized by feathered bodies, turkey-like heads, Edward Scissorhands-like claws, and plump pot-bellies."

    There's been some media pick up in Live Science and in the Pittsbugh papers, reflecting the local affiliation of another team member, Matt Lamanna of Carnegie Museum of Natural History. The Philadelphia Inquirer, though, seems to have passed on it. Meanwhile Fox News cuts to the chase with a classic headline over the Live Science piece: Funny-looking dinosaur found in China.

    What's more, Ken and his wife have just had a son. Congratulations!

    By Oliver Morton.

    Illustration: Mark A. Klingler, Carnegie Museum of Natural History.


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