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Ardipithecus : le singe descend de l'homme !

2009-11-28T19:01:30Z

Non ce n'est pas une blague ou une hypoth�se philosophique saugrenue. Mais la cons�quence d'une d�couverte scientifique qui a fait le tour du monde sans qu'on ne mesure sa r�elle port�e.

Qu'a-t-on a d�couvert ? Une �quipe scientifique internationale a mis � jour Ardi, le squelette d'une hominid�e vivant en �thiopie il y a 4,4 millions d'ann�es. Publi� dans un dossier sp�cial de la revue am�ricaine, Science, en date du 2 octobre, le cas Ardi fait aussit�t le tour de la presse mondiale, de l'�dito du New York Times � 20 minutes en passant par Al Jazeera (voir les liens infra). Beaucoup plus vieille que Lucy (2,5 M), Ardi r�v�le que notre plus vieil anc�tre �tait d�j� bip�de : il marchait sur ses deux pieds et non � quatre pattes.

En quoi cela bouleverse-t-il notre vision des origines ? Jusqu'ici on s'imaginait que l'homme, issu de la m�me branche que les grands singes, s'�tait diff�renci�, en se dressant sur ses pieds (vers 2,5 millions d'ann�es). Si l'anc�tre commun de l'homme et des singes, que l'on se repr�sentait comme un grand singe, �tait d�j� debout, alors, il faut inverser le sch�ma de l'�volution.

La d�couverte d'Ardi r�fute-t-elle la th�orie de l'�volution de Darwin ? Les cr�ationnistes am�ricains et musulmans se sont d�j� empar�s du cas de Ardi pour clamer que Dieu avait cr�� l'homme � son image - debout. En r�alit�, si Ardi bouleverse le sch�ma de l'�volution, il confirme le principe darwinien d'une origine animale de l'humanit� et d'une diff�renciation des esp�ces s'adaptant � la modification de leur milieu.

En quoi cela nous concerne-t-il directement ? Ardi nous prive du grand �v�nement qui permettait de penser l'�mergence de l'humanit�. Si la station droite - associ�e au d�veloppement de l'outil et du cerveau - ne suffit plus � distinguer l'homme et l'animal, alors il faut se forger une nouvelle id�e du propre de l'homme sur la base d'un partage de l'ensemble de ses comp�tences avec les grands singes.

En mettant en perspective la cas de Ardi, Philosophie magazine montre dans num�ro � para�tre jeudi 25 novembre que c'est toute notre vision des origines qui est boulevers�e et interroge les sp�cialistes (pal�ontologues, �thologues et philosophes) sur leur conception renouvel�e du propre de l'homme. Avec Yves Coppens, Franz de Waal, Dominique Lestel, Peter Singer, Etienne Bimbenet, Robert Legros et Pascal Engel.

L'�v�nement

1er octobre : une conf�rence de presse est tenue � Washington aux �tats-Unis, et simultan�ment � Addis-Abeba en �thiopie.

2 octobre : parution du num�ro sp�cial de Science consacr� � Ardipithecus ramidus. 11 articles, r�dig�s par 47 scientifiques venant de 10 pays diff�rents, y exposent les r�sultats de plus de quinze ann�es de recherche. On d�couvre en particulier qu'Ardi - surnom donn� au squelette le plus complet qui a �t� retrouv� - �tait d�j� capable de se tenir debout. On trouve sur le site du Guardian une reconstitution saisissante de la marche d'Ardi.

La couverture de l'�v�nement dans la presse

La presse internationale s'empare aussit�t de l'information : la d�couverte phare est relay�e dans la journ�e par : � le New York Times, dans un article du 1er octobre et qui lui consacre m�me son �ditorial le 7 � Time � National geographic � The Guardian � Le Monde � Sciences et Avenir � l'Express � 20 minutes

puis dans les jours suivants par : � Courrier international (reprenant le Washington Post) � France soir � Les �chos � Le Figaro

La pol�mique avec les cr�ationnistes

Cette d�couverte, et notamment la d�claration du biologiste Owen Lovejoy, « l'homme ne descend pas du singe », jette aussit�t le trouble : elle est relay�e sans pr�caution par certains journaux, tel que le Metro canadien.

3 octobre 2009 : Al Jazeera fait part de la d�couverte d'Ardi sous le titre « Ardi r�fute la th�orie de Darwin » Le docteur en g�ologie Zaghloul El-Naggar y affirme que « les Occidentaux reviennent � la raison, apr�s avoir trait� les origines de l'homme dans une perspective mat�rialiste et ni� la religion ». Il ajoute que l'�ge de la Terre n'exc�de pas 400 000 ans et que l'�ge de Ardi (4,4 millions d'ann�es) est exag�r�. Le m�me jour, sur son site, le philosophe am�ricain anti-cr�ationniste Richard Dawkins attire l'attention sur cette r�cup�ration.

Les cr�ationnistes am�ricains ne sont pas en reste

6 octobre : le cr�ationniste am�ricain Chris Esparza, qui �crit pour le Dallas Christian Living Examiner, titre son article « le plus vieux squelette humain r�fute la th�orie du cha�non manquant »

7 octobre : la journaliste Ann Gibbons, de Science, publie un article qui r�tablit, contre les cr�ationnistes, le sens de la d�couverte scientifique : le dernier anc�tre commun que nous partageons avec le chimpanz� ne ressemblait pas � un chimpanz�, on ne peut donc pas prendre mod�le sur les singes actuels pour se repr�senter notre lointain anc�tre.

Ressources p�dagogiques :

� pr�sentation, en fran�ais, du num�ro sp�cial de Science sur le site de l'Aaas (American Association for the Advancement of Science) � compte-rendu de la d�couverte et nombreuses ressources sur la Pr�histoire � de nombreuses vid�os et reconstitutions sur le site de la cha�ne Discovery Channel, qui a consacr� un documentaire exceptionnel � la d�couverte d'Ardi (diffus� aux �tats-Unis le 11 octobre) � site Web consacr� par Science � Ardi � toujours sur le site de Science, une vid�o de l'analyse d'Ardi avec l'interview de son principal d�couvreur, Tim White � National Geographic : nouveau sch�ma de l'�volution et exploration des parties du corps de Ardi

Le singe descend de l'homme

2009-11-27T09:45:48Z

C'est un coup de tonnerre dans le monde scientifique, une th�orie surprenante vient de voir le jour.

Nous la devons � C.Owen Lovejoy. Ce n'est pas un inconnu. Il a collabor� d�j� aux travaux sur le squelette de la c�l�bre Lucy. Celle-ci avait 3millions d'ann�es. Ce qui n'est pas le cas d'Ardi, ce squelette d�couvert r�cemment. Cette femelle (ardipithecus ramidus) a �t� d�couverte par Tim White et son �quipe en Ethiopie, en 1992. lien Le 2 octobre dernier, c'est la revue « sciences » qui lan�ait le pav� dans la mare : selon C.Owen Lovejoy et son �quipe de scientifique, Ardi (pithecus) �tait plus vieille que Lucy d'1,4 millions d'ann�es. D'une hauteur de 1,20 m�tre pour un poids de 50 kg, Ardi est donc � ce jour notre plus vieil anc�tre connu. Elle avait des mains plus petites que celles des grands singes, et son cerveau, assez petit, �tait de la taille de celui d'un singe bonobo. Capable de se balancer de branche en branche, avec ses 4 membres, elle pouvait �galement se d�placer debout. Nous savions d�j� que nos anc�tres �taient noirs, ce qui a �t� prouv� par des �tudes fond�es sur l'ADN, et que j'avais relat� dans un article paru dans AgoraVox. lien Mais voici venir le meilleur. Lovejoy pr�tend que ce serait le singe qui descendrait de l'homme et non le contraire. Il affirme : « les gens ont tendance � croire que nous descendons de quelque chose qui ressemble � un singe. En fait, c'est plut�t le contraire : les singes descendent de quelque chose qui ressemble plut�t � un humain, enfin, d'une lign�e commune qui a donn� l'humain. Une id�e trop populaire est que les humains sont des sortes de chimpanz�s modifi�s ; En �tudiant Ardi, nous avons appris surtout que nous ne pouvons apprendre ou mod�liser l'�volution humaine � partir de l'�tude des chimpanz�s et des gorilles ». La th�orie classique disait que notre anc�tre avait d�cid� de se mettre debout lorsqu'il � quitt� la foret, et avait choisi la plaine. Dans le cas d'Ardi, �� ne tient pas, car il s'av�re qu'elle vivait dans un environnement bois�. Si elle continuait a vivre dans les arbres alors qu'elle �tait bip�de, c'�tait pour se nourrir, et pour le sexe. lien En effet, si l'on observe les chimpanz�s, on s'aper�oit qu'ils doivent se mesurer les uns aux autres pour gagner le cœur de la belle. Lorsqu'un male est moins puissant, il doit devenir plus fut�, et va proposer une nourriture app�tissante � la femelle afin de la s�duire ; Lien. Dans le cas d'Ardi cette strat�gie �tait dangereuse, car le postulant s'exposait ainsi aux pr�dateurs, et les males pouvaient avoir bien plus de chances de succ�s s'ils pouvaient tenir la nourriture entre leurs mains. Il leur fallait donc pour cela se d�placer sur deux jambes. Ensuite, il fallait s�duire la belle lorsque le male dominant avait le dos tourn�. Selon Lovejoy, « la bip�die aurait donc comme principale origine le sexe ». Cette th�orie venant d'un « Love-Joy », ne devrait pas surprendre ! Et pourtant nous pourrions bient�t envier les chimpanz�s. Dans un article paru dans le monde, le 4 d�cembre 2007, Elise Barthet raconte une exp�rience �tonnante faite par le professeur Tetsuro Matsuzawa. lien Il affirme « beaucoup de gens croient na�vement que les humains sont les cr�atures les plus intelligentes sur cette plan�te. La recherche que j'ai fait prouve tr�s clairement qu'ils se trompent » La m�me exp�rience a �t� r�alis�e avec d'un cot� 12 �tudiants, et de l'autre 6 chimpanz�s. En 1/5�me de seconde une s�rie de chiffres de 1 � 9 dispos�s d'une mani�re al�atoire, apparait sur un �cran tactile. Les chiffres sont remplac�s ensuite par des carr�s blancs. Il faut donc restituer un � un les chiffres dans un ordre croissant. Les performances des chimpanz�s ont largement d�pass� celle des �tudiants, en mati�re d'exactitude et de vitesse. Le professeur Matsuzawa va plus loin en sugg�rant que « les �tres humains �taient probablement dot�s � l'origine des m�mes capacit�s de m�morisation que les chimpanz�s. Ils auraient perdu cette qualit� au fil de l'�volution, renon�ant � leurs anciennes comp�tences pour en acqu�rir de nouvelles ». Alors, comme disait un vieil ami africain : « la m�re du plus fier des coqs n'�tait jamais qu'un œuf au d�part ».

Ink found in Jurassic-era squid

2009-08-20T06:12:55Z

Ink found in Jurassic-era squid

The specimen is now in the British Geological Survey collection Palaeontologists have drawn with ink extracted from a preserved fossilised squid uncovered during a dig in Trowbridge, Wiltshire.

The fossil, thought to be 150 million years old, was found when a rock was cracked open, revealing the one-inch-long black ink sac.

A picture of the creature and its Latin name was drawn using its ink.

Dr Phil Wilby of the British Geological Survey said it was an ancient creature similar to the modern-day squid.

"The structure is similar to ink from a modern squid so we can write with it," he said.

'Medusa effect'

The find was made at a site which was first excavated in Victorian times where thousands of Jurassic fossils with preserved soft tissues were found.

Dr Wilby, who led the excavation, said : "We think that these creatures were swimming around during the Jurassic period and were turned to stone soon after death. It's called the Medusa effect."

It is difficult to imagine how you can have something as soft and sloppy as an ink sac inside a rock that is 150 million years old

Dr Phil Wilby Experts believe one possibility is that thousands of the creatures congregated in the area to mate before being poisoned by algae in the water.

Remains of a different species of squid have also been found, suggesting the carcasses attracted predators to feed on them and they in turn also died.

Dr Wilby said : "They can be dissected as if they are living animals, you can see the muscle fibres and cells.

"It is difficult to imagine how you can have something as soft and sloppy as an ink sac fossilised in three dimension, still black, and inside a rock that is 150 million years old."

The specimen is now in the British Geological Survey collection in Nottingham.

Part of the ink sac has been sent to Yale University in America for more in-depth chemical analysis.

The Mystery Ape of Pleistocene Asia

2009-06-25T11:59:04Z

The mystery ape of Pleistocene Asia Russell L. Ciochon

Russell L. Ciochon is chair of anthropology at the University of Iowa, Iowa City, Iowa 52242, USA. This Essay is based on a contribution to the book Out of Africa I : Who, When and Where ? (eds, Fleagle, J. G. et al. Springer, 2009). Email : russell-ciochon@uiowa.edu

Fossil finds of early humans in southeast Asia may actually be the remains of an unknown ape. Russell Ciochon says that many palaeoanthropologists - including himself - have been mistaken.

Fourteen years ago, a Nature paper by my colleagues and I described a 1.9-million-year-old human jaw fragment from Longgupo in Sichuan province, China1. The ancient date in itself was spectacular. Previous evidence had suggested that human ancestors arrived in east Asia from Africa about 1 million years ago, in the form of Homo erectus. Longgupo nearly doubled that estimate. But even more exciting - and contentious - was our claim that the jaw was related to H. habilis, a species of distinctly African origin. If this descendant of H. habilis had arrived so early into southeast Asia, then it probably gave rise to H. erectus in the Far East, rather than H. erectus itself sweeping west to east.

For many years, I used Longgupo to promote this pre-erectus origin for H. erectus finds in Asia. But now, in light of new evidence from across southeast Asia and after a decade of my own field research in Java, I have changed my mind. Not everyone may agree ; such classifications are always open to interpretation. But I am now convinced that the Longgupo fossil and others like it do not represent a pre-erectus human, but rather one or more mystery apes indigenous to southeast Asia's Pleistocene primal forest. In contrast, H. erectus arrived in Asia about 1.6 million years ago, but steered clear of the forest in pursuit of grassland game. There was no pre-erectus species in southeast Asia after all.

The Longgupo site, discovered in 1984, lies 20 kilometres south of the Yangtze River in eastern Sichuan. At the beginning of the Pleistocene (1.8 million to 10,000 years ago) this cave sat near the northern range of a subtropical forest as rich with life as any in contemporary Africa. Unsurprisingly, the mammalian fossils dug up from Longgupo belonged to the subtropical Stegodon-Ailuropoda fauna found throughout the subtropical forested region south of China's Qinling Mountains (see map). The name comes from two common members - the extinct elephant-like Stegodon and the bear-like giant panda, Ailuropoda. It includes primates such as the extinct giant ape Gigantopithecus, as well as the ancestors of the living orangutan (Pongo) and gibbon (Hylobates).

But Longgupo also yielded a mystery jaw fragment, including the fourth premolar and the first molar. Although obviously primate, the worn enamel surfaces made precise classification difficult. Some had called it an ape whereas others saw an early human. In 1992, colleagues and I were invited to Longgupo to provide a reliable age determination and to help understand the palaeoanthropology.

The 1.8-million-2-million-year-old jaw was smaller than that of any known orangutan, living or extinct. We also compared it with primate dental fossils from the site of Lufeng, in neighbouring Yunnan province. Lufengpithecus was of the right size and general morphology, but the age was wrong : Lufeng and similar sites belonged to the late Miocene period, about 7 million-9 million years ago. Some possible stone tools found at the site seemed to support a human classification. Asian H. erectus was the obvious possibility, but the size, tooth proportions and root structure were not quite right. Dissatisfied with the usual regional comparisons, we looked to Longgupo's possible links with early African humans such as H. habilis, whose Great Rift Valley fossils are as old as 2.3 million years. Our Nature announcement1 thus presented the Longgupo jaw as a newcomer to the Stegodon-Ailuropoda fauna : an African hominin more primitive than H. erectus.

Pre-erectus claims We weren't the first or last to suggest that a pre-erectus African hominin migrated to east Asia. In the 1940s and 1950s pre-erectus African claims were made for fossils from Sangiran, on Java, Indonesia. Early in Sangiran's long history of H. erectus discoveries, a couple of massive jaws seemed similar to those of South African australopiths - they were coined 'Meganthropus'. But as more fossils were discovered at Sangiran, it became clear that the Meganthropus jaws were merely a local variant of H. erectus.

More than a decade later, with some distance from the subject, the teeth looked distinctly more ape-like. Just this year, claims for a pre-erectus African in Asia have also surfaced to explain the evolution of Indonesia's Homo floresiensis, popularly known as the Liang Bua 'hobbit'. Discovered in 2003, and dated to just 95,000 to 17,000 years ago, the Liang Bua skeleton is a diminutive species significantly different from all other known humans. The discoverers proposed that the diminutive H. floresiensis evolved from a southeast Asian H. erectus group that became isolated on Flores : faced with limited resources, the erectus group dwarfed to match the small-island conditions. However, recent studies of Liang Bua wrist and foot bones reveal primitive anatomies reminiscent of H. habilis or Australopithecus, again leading some to propose a pre-erectus African origin for the species. The problem is that no comparable wrist or foot bones are known for H. erectus, making it impossible at this time to exclude a local variant of H. erectus as the ancestor of the Liang Bua 'hobbit'.

So our claim of a pre-erectus African hominin living in east Asia fell into a long line of such arguments. It was met with healthy scepticism. We were first faced with the response that Longgupo was an orangutan, but we were able to show that the two teeth lay significantly outside the orangutan range of variation2, 3. Later, we had to field a serious proposal that Longgupo belonged to Lufengpithecus4, 5. Although the age disparity remained troubling, the dental similarities could not be denied. I began to imagine a mystery ape as a possible solution to the problem.

W. FERNANDES Then in spring 2005, I met with Wang Wei, director of the Guangxi Natural History Museum, to examine his collection of 33 primate teeth from Mohui cave in Bubing Basin, south China. Wang's excavations produced an excellent sample of the Stegodon-Ailuropoda fauna. Quickly I could see that 15 teeth were those of Gigantopithecus, and 10 were probably Pongo. The remaining eight specimens did not fit with any known east Asian Pleistocene primate.

Some 15 years earlier, I had worked hard to show that Gigantopithecus had crossed paths with H. erectus ; I wrote a book in 1990 proposing this relationship (Other Origins : The Search for the Giant Ape in Human Prehistory) and a few years later had documented evidence of the species' co-existence. In my mind the two were firmly linked. But more than a decade after the discovery, with some distance from the subject, the teeth in Wang's lab looked distinctly more ape-like than hominin.

Teething problems Without the assumption that Gigantopithecus and H. erectus lived together, everything changed : if early humans were not part of the Stegodon-Ailuropoda fauna, I had to envision a chimpanzee-sized ape in its place - either a descendant of Lufengpithecus, or a previously unknown ape genus. The Mohui mystery teeth surely belonged to an unknown ape, as did Longgupo, and other human-like teeth often identified from similar cave fossils. Although I no longer consider the Longgupo jaw to be human, the two stone tools still stand as described. They must have been more recent additions to the site.

The mystery ape concept is bolstered by looking at definitive H. erectus finds in east Asia. Our knowledge comes mainly from two sites : Zhoukoudian near Beijing, which lies well north of the primal forest, and Sangiran in Java, which lies well south of it. Each site represents hundreds of thousands of years of H. erectus occupation : Sangiran beginning as early as 1.6 million years ago, Zhoukoudian beginning about 780,000 years ago6. Neither site preserves Stegodon-Ailuropoda fauna or mystery ape teeth. Homo erectus, it seems from this perspective, hunted grazing mammals on open grasslands, and did not or could not penetrate the dense subtropical forest. In fact, there is no record of early hominins living in tropical or subtropical forested environments in Africa or Asia.

In resolving the mystery, two other Asian sites come to mind : Jianshi (Hubei province, China) and Tham Khuyen (Lang Son province, Vietnam). At both sites, teeth labelled variously as Australopithecus, H. erectus and Meganthropus are most likely to be the mystery ape instead. Others have come to similar conclusions7 ; a 2009 paper identifies a tooth from Sanhe Cave (Chongzuo, Guangxi province, China) as belonging to an unidentified ape8.

In this call to reassess historical assemblages, it is worth remembering the story of 'Hemanthropus'. Legendary fossil collector Ralph von Koenigswald created this hominin taxon in 1957, based on isolated fossil teeth found in apothecary shops across southeast Asia. Von Koenigswald viewed Hemanthropus as a distant relative of African Australopithecus. Later research revealed that these were worn or atypical orangutan teeth and Hemanthropus was quickly abandoned. But, had von Koenigswald actually discovered evidence of the mystery ape ? In October 2005, I examined the original Hemanthropus collection. Among the many worn orangutan teeth I found several small ape teeth that very closely resembled the mystery ape teeth from Mohui. Perhaps von Koenigswald was the first to lay hands on the mystery ape.

The question remains : is there only one mystery ape or possibly more ? It seems that there was as much diversity of apes in the southeast Asian Pleistocene as in Africa today. In modern Africa there is one large ape (the gorilla) and two smaller apes (the chimpanzee and bonobo) ; in Asia during the Pleistocene and recent times, we have one very large ape (Gigantopithecus), one large ape (the orangutan), at least one smaller ape (mystery ape) and finally a tiny ape (the gibbon).

The next step is to consider the mystery ape fossils as a group and see how they fit into the evolutionary history of the range of southeast Asian apes. Wang will head up this team effort, along with Chinese and international colleagues, including myself. Museum collections holding potential mystery-ape evidence will be examined, including those in Hanoi, Jianshi, Beijing and Frankfurt. Wang's ongoing excavations at cave sites in Guangxi's Bubing Basin are yielding new evidence with every passing day. Possibly, there will be a chance to announce a new southeast Asian fossil ape in some future issue of this journal.

Orangutans to replace chimpanzees as our closest relatives

2009-06-22T14:30:51Z

A quick heads up for those interested in human evolutionary history : In Journal of Biogeography Grehan and Schwartz presents evidence for the hypothesis that the closest living relative of humans is the orangutan, and not the chimpanzee.

The phylogenetic tree of the relationship of these four apes would then look like figure B, rather than the usual one in figure A :

My own beautiful cladograms.

Their conclusion is based on morphological data, rather than molecular data (DNA), and they counter that the well-known percentages of DNA that humans share with other apes are "primitive retentions" (older traits with a deeper evolutionary past shared by a larger group of species). Humans share 98.4% with chimpanzees, 97.5% with gorillas, and 96.5% with orangutans.

The morphological data on which their study is based include features of anatomy, reproductive biology, and behavior. For example, among the great apes only humans and orangutans have thick tooth enamel, long hair, male facial hair, concealed ovulation, a preference for private, face-to-face mating, and an ability to construct shelters and beds.

No doubt this is going to cause a fair amount of debate in the scientific community. Which is great. Stay tuned.

Reference : John R. Grehan and Jeffrey H. Schwartz (2009). Evolution of the second orangutan : phylogeny and biogeography of hominid origins Journal of Biogeography, in press.

Could the orang-utan be our closest relative ?

2009-06-18T22:25:57Z

17 June 2009 by Graham Lawton

Magazine issue 2713.

Are we the "third chimp" or the "second orang" ? Controversial new research suggests that we may be more closely related to the orang-utan than realised.

THESE days, we tend to accept without question that humans are "the third chimpanzee". The term, coined by author Jared Diamond, refers to the notion that our closest relatives are the two chimpanzee species - the common chimp and the bonobo. But could we actually be "the second orang" - more closely related to orang-utans than chimps ?

That is the controversial claim made this week by Jeffrey Schwartz of the University of Pittsburgh in Pennsylvania and John Grehan of the Buffalo Museum of Science in New York (Journal of Biogeography, DOI : 10.1111/j.1365-2699.2009.02141.x, in press)

The idea flies in the face of mainstream scientific opinion, not least a wealth of DNA evidence pointing to our close relationship to chimps. Schwartz and Grehan do not deny the similarity between human and chimp genomes, but argue that the DNA evidence is problematic and that traditional taxonomy unequivocally tells us that our closest living relatives are orang-utans.

The researchers say the evidence of genetic similarity between humans and chimps is problematic Human evolution and phylogenomics researchers have so far given the paper a rough reception. Some declined to comment on it, saying they did not want to dignify the paper. One described it as "preposterous nonsense" and another as "loopy".

Others were less dismissive, though, agreeing that at least some of the ideas were worth discussing, if only to confirm the overwhelming evidence in favour of the orthodox view.

The Journal of Biogeography's editors defended the decision to publish the paper, arguing that it is the best way to subject Schwartz and Grehan's argument to proper scientific scrutiny. Editor Robert Whittaker told New Scientist he had done some "soul searching" but eventually decided it was best to air the ideas.

In the orthodox account of human origins, our species belongs to a group of African apes that also includes chimps, bonobos and gorillas. Chimps and bonobos are our closest living relatives, sharing a common ancestor with us up to about 6 million years ago (see diagram). This version of events is strongly supported by DNA evidence showing that the human genome sequence is most similar to that of the chimp, followed by gorillas, with orangs the least similar of the three.

Schwartz and Grehan say that genome similarities cannot be taken as conclusive evidence of the closeness of our evolutionary relationships to the other great apes. In their scenario, around 13 million years ago, an orang-like ape lived across a huge swathe of land stretching from southern Africa to south-east Asia via southern Europe and central Asia (see map). This population evolved into different species, before extinctions in Europe and central Asia split the original geographical range and left rump populations in east Africa and south-east Asia. The African population evolved into the human lineage while the Asian one evolved into orang-utans.

In this scenario, the other African apes are a separate lineage that split off from ours long before 13 million years ago, making orangs our closest living relative and the chimps and gorillas more distant.

This claim hinges on two contentious arguments. One is that DNA sequence similarity is not necessarily an indicator of evolutionary relatedness. The other is that, biologically, humans are more like orangs than chimps.

The first of these is the most problematic, as almost everybody accepts genome sequences as the most reliable indicator of evolutionary relatedness. Humans share 98.4 per cent of their DNA with chimps, 97.5 per cent with gorillas and 96.5 per cent with orang-utans. This is widely taken as unassailable proof.

Grehan, however, argues that this is not scientifically justified. He points out that traditional taxonomy makes a distinction between two types of similarity - "derived novelties" and "primitive retentions". Derived novelties are traits shared by two closely related species and are taken to have evolved in a recent common ancestor. Primitive retentions are older traits with a deeper evolutionary past shared by a larger group of species.

The problem with molecular systematics, says Grehan, is it fails to distinguish between the two. "It does not matter that more DNA similarities may be found between humans and chimpanzees if these similarities are really primitive retentions," he says. The fact that humans and orang-utans are less genetically similar could be because orangs evolved more rapidly after splitting from a common ancestor with hominins.

Nonsense, says Maryellen Ruvolo, a human evolutionary biologist at Harvard University. "We know a lot about how DNA sequences change over time," and can distinguish between primitive retentions and derived novelties. Furthermore, she argues, the latest DNA sequence information indicates that humans share more derived novelties with chimps than with orang-utans.

David Reich, a geneticist at Harvard, agrees. "The molecular data overwhelmingly reject the notion that orang-utans are our closest relatives," he says.

The other half of the argument is a taxonomic analysis comparing the anatomies of humans, chimps, bonobos, orangs and 14 extinct species of ape. Based on this, Grehan and Schwartz argue that Homo species, orangs and australopithecines cluster into one "clade" with chimps and gorillas in another.

They say that many anatomical features we share with orang-utans appear to be recent novelties rather than primitive retentions. "There are a few features uniquely shared with chimps, but the bulk come out as [shared with] orangs," says Schwartz.

There are a few features shared with chimps but the bulk come out as shared with orangs These include features of anatomy, reproductive biology and behaviour. For example, among the great apes only humans and orangs have thick tooth enamel, long hair, male facial hair, concealed ovulation, a preference for private, face-to-face mating, and an ability to construct shelters and beds. Mainstream opinion is these are due to parallel evolution.

According to Robin Crompton, an anatomist at the University of Liverpool, UK, Grehan and Schwartz's selection of species for phylogenetic analysis is "strange", and misses out key extinct species such as Proconsul, considered to be the ancestor of all great apes. Even so, the paper appears to contain some good ideas, he says. "The biogeographic ideas are really quite interesting."

Ultimately, Grehan and Schwartz accept their claims are extraordinary but say they are worthy of proper consideration. "It's up for testing and debate," says Schwartz.

Chimps still new to the family The idea that chimps are our closest living relatives is so entrenched that it is easy to forget that the notion was only accepted into the story of human evolution relatively recently.

Darwin himself proposed that humans evolved in Africa and shared a common ancestor with chimps and gorillas. Later biologists disagreed, though, arguing that the human lineage was so different from the other great apes that it must have been evolving on a separate trajectory for many millions of years.

In the mid-1960s, palaeontologists Elwyn Simons and David Pilbeam proposed that an extinct ape called Ramapithecus, which lived in what is now India and Pakistan up to about 8.5 million years ago, was a close relative of humans and possibly a direct ancestor. This gained widespread acceptance until new specimens showed it had an orang-utan-like face, whereupon the idea was quickly dropped.

Around the same time, molecular techniques started hinting at a close affinity between humans and chimps. This has been the orthodox position for more than 30 years.

Not everybody accepts it, however. Jeffrey Schwartz of the University of Pittsburgh, Pennsylvania, has been arguing since the early 1980s that orangs are our closest living relatives (Nature, DOI : 10.1038/308501a0). His latest research paper continues that theme.

New Questions About Purpose of Big Brains

2009-06-11T15:59:41Z

New Questions About Purpose of Big Brains

By Robin Lloyd, LiveScience Senior Editor

posted : 04 June 2009 09:25 am ET

Group living, as opposed to a solitary life, apparently taxes the brain. In fact, sociality has made brains bigger over evolutionary time across numerous groups of animals, a lot of biologists and anthropologists have figured over the years.

This "social brain hypothesis" may pertain in some groups, but overall it's false when it comes to the natural history of carnivorous mammals such as cats, dogs, weasels, bears and their relations, two evolutionary biologists now say.

It's true that bigger brains - in such animals as whales, dolphins, primates and birds - are associated with greater behavioral flexibility and adaptability to new environments. But big brains relative to overall body mass (this ratio is referred to as encephalization) also take a lot of energy to maintain. And some brains tend to get smaller when animals are domesticated or are hunted less by other animals. So the overall trend has been hard to discern.

John Finarelli of the University of Michigan and John Flynn of the American Museum of Natural History in New York sought to work out the relationship on a bigger data set that anyone had previously devised - including 289 terrestrial carnivores, about half of which were fossil (extinct) species. They laid data on sociality, body mass and brain size over the evolutionary tree for all carnivores to investigate the relationship between brain size and sociality.

They found the relationship might hold up among living members of the Canidae family (wolves, foxes, coyotes and jackals), but that's about it. For instance, sociality should be widespread among musteloids (weasels, raccoons, skunks and red pandas) and bears, which have had brain to body mass ratio increases over the course of their evolution. But they aren't. All bears in fact are solitary and the musteloids are mostly "nonsocial."

And while brain size does scale up from small cats to large cats, hyenas are large-brained but also fairly solitary and mongooses are small-brained and usually social.

Overall, Finarelli and Flynn found at least six separate changes in brain sizes for the group across their evolutionary history.

"The idea that sociality played a causative role in the expansion of relative brain size is not valid for this clade [Carnivora] as a whole," the authors write in the May 25 early online issue of the journal Proceedings of the National Academy of Sciences.

Even in Canidae, it could be that increasing brain-size facilitated more social behaviors (rather than sociality causing increasing brain sizes), or perhaps canids evolved larger brains to enhance their social behaviors. Finarelli said he was surprised at how complicated the evolutionary transformations around brain size turned out to be. "I thought at the outset that there would end up being a few instances of increased encephalization, but the number of these, the fact that there were instances of decreased encephalization, and that consistent scaling parameters (that is, how fast brain volume changes as you add body mass) defined the changes in some groups was a pleasant surprise."

So why do brain sizes vary ? "That is the $64,000 question," Flynn told LiveScience. "Evolutionary change in encephalization is a widely observed phenomenon, but has been very hard to explain." And what about primates ? The relationship between sociality and brain size in this group remains untested, Flynn said.

"Increased brain size may mean different things to different groups, depending on unique evolutionary histories, ecologies, life history attributes etc.," he said. "That is to say, it might be that seeking simple, one-size-fits-all explanations across all mammals (or all amniotes [animals such as birds, mammals and reptiles that give birth to young inside eggs]) has been the problem all along. Nevertheless, seeking general explanations (and then testing them with all available data), within clades or across groups, is a valuable goal of evolutionary studies."

The research was funded by the National Science Foundation, AMNH, the Brown Family foundation Graduate Fellowship and the University of Michigan Society of Fellows.

Neandertals Babies Didn't Do the Twist

2009-05-04T13:16:57Z

By Ann Gibbons

ScienceNOW Daily News

20 April 2009

Giving birth is more difficult--and dangerous--for modern humans than for any other primate. Not only do human mothers have to push out babies with unusually big heads, but infants also have to rotate to fit their heads through the narrow birth canal. Now, a new virtual reconstruction of the pelvis of a Neandertal woman suggests that Neandertal mothers also had a tough time giving birth to their big-headed infants--but the babies, at least, didn't have to rotate to get out. Once upon a time, a major shift took place in the evolution of childbirth. Fossil female pelvises of a 1.2-million-year-old Homo erectus, a 3.1-million-year-old australopithecine, and a 500,000-year-old archaic modern human all contain oval birth canals that are widest transversely--from side to side--when viewed from the top. But modern women's birth canals, though also oval, change shape halfway down the birth canal so that they are widest from front to back at the bottom, near the pelvic outlet. This means that the baby has to rotate its head to fit as it moves through the birth canal. If a baby fails to rotate, another part of its body, such as its shoulders, hands, or feet, may obstruct the birth canal, which is painful and dangerous for the mother and infant.

Like many other researchers, paleoanthropologist Timothy Weaver of the University of California, Davis, thought the shift to this more complicated rotational birth predated the split between modern humans and Neandertals. That's because Neandertals, which lived until 30,000 years ago in Europe, also had big heads and, presumably, used the same evolutionary strategy to deliver their big-brained babies. But it has been difficult to test this idea. The only known female pelvis of a Neandertal, discovered in 1929 near Tabun, Israel, is fragmentary. Two earlier reconstructions of this partial pelvis suggested that Neandertals also had rotational birth, but the fossil is missing its sacrum and, hence, the birth canal.

Now, new tools have given Weaver a way to work around that problem. Collaborating with Jean-Jacques Hublin at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, Weaver got permission to make computed tomography-scans of the pelvis, which is kept at the British Museum in London. The two researchers were able to refit the pieces of the pubis, ischium, and ilium together in a three-dimensional, virtual reconstruction. They also used landmarks on the pelvic fragments to compare the pelvis to those of modern humans--and to predict the size and shape of the missing pieces, such as the sacrum and dimensions of the pelvic outlet.

The reconstruction suggests that the pelvis of the Tabun Neandertal was widest from side to side all the way down the birth canal, more like that of Homo erectus or australopithecines than modern humans. And that means that although Neandertal mothers still had difficult births because of their babies' large heads, their babies did not rotate in the womb, the team reports online today in the Proceedings of the National Academy of Sciences.

So why would our ancestors evolve such a complicated birth in the first place ? Other research shows that they had to balance pressures to adapt to the hot climate in equatorial Africa--and tall, slender-hipped humans thermoregulate in the heat better than short, stocky humans (whose physiology retains heat better in the frigid latitudes). By evolving a birth canal that is wide front to back, our ancestors were able to accommodate both narrower pelvises and the delivery of big-brained babies, suggests Weaver.

But it will take more than a virtual pelvis to convince other researchers. "I don't know if I believe the reconstruction," says paleoanthropologist Karen Rosenberg of the University of Delaware, Newark. She and others have questions about the accuracy of the reconstruction of the missing parts of the pelvis, which are critical for proving there was no rotation. "Given the poor preservation of the Tabun pelvis, ... this is a bold claim," says anthropologist Marcia Ponce de Le�n of the University of Zurich in Switzerland. She does agree, however, with one conclusion : "Birth was equally difficult in Neandertals as in modern humans," with or without a twist.

Twist and shout. This virtual reconstruction of a Neandertal pelvis suggests that Neandertal babies didn't rotate during birth.

CREDIT : TIMOTHY WEAVER AND JEAN-JACQUES HUBLIN

L'erreur de DARWIN

2009-04-05T23:39:18Z

Nouveaut�

�dition Le Jardin des livres

L'erreur de DARWIN

Dr Hans-Joachim ZILLMER

356 Pages

Sp�cialis� dans l'arch�ologie pr�-diluvienne, le Dr Zillmer nous emm�ne dans une enqu�te aux quatre coins du monde pour nous montrer que les arch�ologues classiques ont toujours trich�, en laissant de c�t� les d�couvertes « bizarres » qui ne collaient pas � la chronologie darwienne !

Comment en effet expliquer la pr�sence d'outils humains dans des strates aussi vieilles que celles du dernier �ge glaciaire ? Pourquoi l'antarctique n'�tait-il pas recouvert de glace auparavant ? Et surtout comment expliquer que les c�tes de l'antarctique figurent sur les cartes maritimes anciennes, comme si elles n'avaient jamais �t� recouvertes de glace ?

Comment expliquer aussi ce sceau sum�rien, vieux de 4 500 ans, qui montre l'emplacement de toutes les plan�tes du syst�me solaire alors qu'� l'�poque on ne pouvait m�me pas les distinguer � l'oeil nu ? Et comment justifier les traces de pas humains � c�t� de celles d'un dinosaure, d�couvertes par centaines dans les plaines texanes de la Paluxy River et ailleurs dans le monde ?

A toutes ces questions qui embarrassent la science politiquement correcte d'aujourd'hui, et � bien d'autres, ce livre r�pond de mani�re extraordinaire en mettant en pi�ces la th�orie de Darwin. Car le Dr Zillmer a �t� forc� de le reconna�tre gr�ce � toutes les d�couvertes « bizarres » du XXe et XXIe si�cles : la th�orie de Darwin ne tient pas...

Le Dr Hans-Joachim Zillmer est pal�ontologue-g�ologue de r�putation mondiale, et membre de l'acad�mie des Sciences de New-York.

les premiers chapitres sont en ligne : www.lejardindeslivres.com

Humans Walked On Modern Feet 1.5 Million Years Ago, Fossil Footprints Show

2009-04-05T23:14:35Z

ScienceDaily (Feb. 27, 2009) - Ancient footprints found at Rutgers' Koobi Fora Field School show that some of the earliest humans walked like us and did so on anatomically modern feet 1.5 million years ago.

The footprints were discovered in two 1.5 million-year-old sedimentary layers near Ileret in northern Kenya. These rarest of impressions yielded information about soft tissue form and structure not normally accessible in fossilized bones. The Ileret footprints constitute the oldest evidence of an essentially modern human-like foot anatomy.

Foot bones are rarely preserved because they are small, encased in flesh, and easily consumed by carnivores. Consequently, our knowledge of foot anatomy and function in early hominins is poor.

To ensure that comparisons made with modern human and other fossil hominid footprints were objective, the Ileret footprints were scanned and digitized by the lead author, Professor Matthew Bennett of Bournemouth University in the United Kingdom.

Published as the cover story in the Feb. 27 issue of the journal Science, the anatomical interpretation is the conclusion of Rutgers Professor John W.K. Harris* and an international team of colleagues.

The authors of the Science paper reported that the upper sediment layer contained three footprint trails : two trails of two prints each, one of seven prints and a number of isolated prints. Five meters deeper, the other sediment surface preserved one trail of two prints and a single isolated smaller print, probably from a juvenile.

In these specimens, the big toe is parallel to the other toes, unlike that of apes where it is separated in a grasping configuration useful in the trees. The footprints show a pronounced human-like arch and short toes, typically associated with an upright bipedal stance. The size, spacing and depth of the impressions were the basis of estimates of weight, stride and gait, all found to be within the range of modern humans.

Based on size of the footprints and their modern anatomical characteristics, the authors attribute the prints to the hominid Homo ergaster, or early Homo erectus as it is more generally known. This was the first hominid to have had the same body proportions (longer legs and shorter arms) as modern Homo sapiens. Various H. ergaster or H. erectus remains have been found in Tanzania, Ethiopia, Kenya and South Africa, with dates consistent with the Ileret footprints.

Other hominid fossil footprints dating to 3.6 million years ago had been discovered in 1978 by Mary Leakey at Laetoli, Tanzania. These are attributed to the less advanced Australopithecus afarensis, a possible ancestral hominid. The smaller, older Laetoli prints show indications of upright bipedal posture but possess a shallower arch and a more ape-like, divergent big toe.

Based on the size and the stride pattern of these newly discovered footprints, the team determined that the individuals responsible would have been approximately 1.75 meters (about 5'9") in height.

*Harris is a professor of anthropology at Rutgers, The State University of New Jersey, member of the Center for Human Evolutionary Studies and director of the Koobi Fora Field Project. Harris is also director of the field school which Rutgers University operates in collaboration with the National Museums of Kenya. From 2006 to 2008, the field school group of mostly American undergraduates, including Rutgers students, excavated the site yielding the footprints.

Journal reference : Robin Huw Crompton and Todd C. Pataky. What can fossil footprints reveal about the evolution of the human foot ? Science, 27 February 2009 ; 323 (5918), 1174 DOI : 10.1126/science.1170916 Adapted from materials provided by Rutgers University.