Vir Angus en Leon

Brianvds

2013-11-04 at 15:34

Ek sou my nie te veel steur aan enigiets wat in Popular Mechanics gepubliseer word nie.

Die vroegste menslike voorouers, net soos die vroegste voorouers van alle lewe op Aarde, het sowat 3.5 miljard jaar gelede geleef.

Wat die tydskrif bedoel met 55 miljoen jaar gelede is nie vir my duidelik nie. Miskien bedoel hulle die vroegste primate? Dit is heeltemal moontlik dat dié oorspronklik uit Asië kom, maar dit maak geen verskil aan die feit dat mense uit Afrika kom nie.

Reply

Angus

2013-11-04 at 16:32

Beste Jan,

Hierdie skrywe van jou bewys so ? paar dinge. Eerstens is dit ? voorbeeld van hoe die mens reageer op inligting. As dit ooreenkom met wat hy glo, laat hy hom maklik aan die neus lei. Weerspreek dit wat hy glo, weier hy om dit eers in aanmerking te neem.

Verkillende wetenskaplikes, geoloë, argeoloë, paleontoloë, bioloë, genetici, se gesamentlike kennis wat hulle verkry het uit jarelange navorsing, dui daarop dat Homo sapiens sy oorsprong in Afrika het. Dit is teenstrydig met hoe Jan Rap dit insien, en daarom verwerp hy dit. ? Artikel verskyn in Popular Mechanics oor fossiele wat volgens die skrywer ouer is as Afrika-fossiele. Dit pas meer in die kraam van Jan Rap se denke, en dit word nou vir hom onteenseglike bewys dat Homo sapiens sy ontstaan in Asië het, en dat al daardie wetenskaplikes verkeerd is.

Dit bewys ook dat baie mense nog die wetenskap verkeerd verstaan. Natuurlik kan enige hipotese of teorie ondersoek en getoets word. Byvoegings, veranderings, ens. kan gemaak word, of indien dit verkeerd bewys word, kan dit geskrap word. Ek sou darem nie die Afrika-teorie met sy tonne navorsing, sommer wil skrap net vir ? artikel in Popular Mechanics nie. In hierdie tydskrif soek ek eerder artikels hoe om son- en windkrag in elektrisiteit om te skakel, of hoe om ? gadget te bou wat my meer kilometer per liter brandstof sal gee. Ek sal dit beslis nie onder ? man soos Dawkins se neus rondwaai en sê: “We! We! Jy’s verkeerd” nie. Dit sal ? gedugte span wetenskaplikes jarelange studie en navorsing verg, om die Afrika-teorie verkeerd te bewys.

Groete,

Angus

Reply

Wouter

2013-11-04 at 17:10

Hello,

Voltaire het dit gehad dat die terme van die debat eers moet bevestig word en net soos Jan Rap nie sy spreekwoordelike spinasie wil eet oor die afgelope 300 jaar se geskiedenis nie in Suid-Afrika nie, is die vraag wat is die moontlikheid dat Jan Rap die verloop van 55 miljoen sal reg kry.

Die terme van die debat voorheen het dit gehad oor die evolusie van die mens en die is deur 'n verskeidenheid van deelnemers hier bevestig as Afrika en is daardie ou, Dawkins.

Uit die argiewe van die New York Times word die volgende bevestig naamlik dat die studie aanvanklik in Nature gepubliseer was.

Die abstrak is soos volg en kan hier gevind word:

http://www.nature.com/nature/journal/v498/n7452/full/nature12200.html 

Nature 498, 60–64 (06 June 2013) doi:10.1038/nature12200

Received 01 February 2013 Accepted 18 April 2013 Published online 05 June 2013

Abstract

Reconstructing the earliest phases of primate evolution has been impeded by gaps in the fossil record, so that disagreements persist regarding the palaeobiology and phylogenetic relationships of the earliest primates. Here we report the discovery of a nearly complete and partly articulated skeleton of a primitive haplorhine primate from the early Eocene of China, about 55 million years ago, the oldest fossil primate of this quality ever recovered. Coupled with detailed morphological examination using propagation phase contrast X-ray synchrotron microtomography, our phylogenetic analysis based on total available evidence indicates that this fossil is the most basal known member of the tarsiiform clade. In addition to providing further support for an early dichotomy between the strepsirrhine and haplorhine clades, this new primate further constrains the age of divergence between tarsiiforms and anthropoids. It also strengthens the hypothesis that the earliest primates were probably diurnal, arboreal and primarily insectivorous mammals the size of modern pygmy mouse lemurs.

Ongelukkig is die koste tot toegang vir Nature redelik duur en het ek nie toegang tot dit nie, maar wel die New York Times wat die bevinding soos volg opsom, aangesien hulle wel toegang tot Nature het en is die New York Times se opsomming soos volg wat weer deur my soos volg opgesom word:

June 5, 2013

Palm-Size Fossil Resets Primates’ Clock, Scientists Say

By JOHN NOBLE WILFORD

A nearly complete skeleton of a tiny, ancient primate — one that weighed no more than an ounce, had a tail longer than its body and would fit in the palm of your hand — is the earliest well-preserved fossil primate ever found, dating back some 55 million years and dialing back the fossil record for primates by an impressive eight million years, a research team declared on Wednesday.

The finding adds weight to the evidence that primates originated in Asia — not Africa — and that they emerged relatively soon after the extinction of the dinosaurs, which happened about 66 million years ago.

The older date brings scientists closer to pinpointing a pivotal event in primate and human evolution: the divergence between the lineage leading to anthropoids — which include modern monkeys, apes and humans — and the one leading to tarsiers.In a report published in the journal Nature, an international team of paleontologists led by Xijun Ni of the Chinese Academy of Sciences in Beijing said that the skeleton, recovered from an ancient lake bed in Hubei Province in central China, set a new benchmark for the time that primates started roaming the planet.

The primate skeleton belongs to a species never seen before, one the researchers identified as the earliest known ancestor of tarsiers — a type of small, nocturnal primate living today in Southeast Asian forests. This unprepossessing early primate was even smaller than today’s smallest primate, the pygmy mouse lemur of Madagascar.

Dr. Ni said in a statement that the findings represent “the first time that we have a reasonably complete picture of a primate close to the divergence,” calling it “a big step forward in our efforts to chart the course of the earliest phases of primate and human evolution.”

K. Christopher Beard, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh and an author of the journal report, said:

“We’ve heard of the ‘out of Africa’ theory of human evolution, but that’s recent history.

So there may now be the ‘into Africa’ problem.”

(The Daily Telegraph het dit soos volg):

Further analysis of the remains could yet make it a human ancestor, according to the scientists.Dr Chris Beard, one of the team who has been studying the fossil at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, said:

“This is an amazingly complete fossil primate for this time period – there is nothing else known from the fossil record that resembles this.

“For the very first time, this fossil shines a light on a part of the primate tree that is very close to the divergence of the lineage that will lead on one hand to living tarsiers and on the other to anthropoids – monkeys, apes and humans.

“The evidence that early primate evolution was restricted to Asia is becoming more compelling by the day.”

While scientists agree that humans first evolved in Africa, the discovery of the fossil now suggests that was not where our part of the primate family started.

Dr Beard believes that our early primate ancestors began developing in Asia before moving to Africa around 35 million years ago.

“Here is a fossil that is very, very close to the evolutionary divergence of tarsiers and anthropoids.

“The heel and foot in general was one of the most shocking parts of this fossil when we first saw it. The foot looks like one from a small monkey, a marmoset.

“The heel bone is the reason we named it Achilles in the end and it looks like one from the earliest anthropoid we had evidence for.“I think what it means is that the common ancestors of anthropoids and tarsiers had features that were more like anthropoids than tarsiers.”

Die New York Times gaan soos volg aan:

How and when did some primates finally make it to Africa, which was an island until as recently as 16 million years ago, to set in motion the emergence of the human species?

There is evidence that 38 million years ago, some primates had apparently crossed open water to colonize the African continent.

The fossil from Hubei does not answer the question of how that happened, but it does give paleontologists plenty to work on for years to come.

The skeleton “differs radically from any other primate, living or fossil, known to science,” Dr. Beard said.

“It looks like an odd hybrid, with the feet of a small monkey, the arms, legs and teeth of a very primitive primate and a primitive skull bearing surprisingly small eyes.”

Jan Rap word herinner daaraan dat sy stelling was dat die mens het sy oorsprong in Benoni...(Alhoewel 'n joke - was die debat oor waar die mens se evolusie plaasgevind het en beide artikels bervestig dit nog steeds Afrika te wees.

Hoe ook al, dit is 'n amazing storie...en bevestig maar weereens hoe vreemd alles hier is...

Daar is selfs Homo Sapiens met die klem op 'sapient' wat nie eers die bestaan van apartheid kan kop nie...

Baie dankie

Wouter

Reply

Wouter

2013-11-04 at 17:39

Hello,

Henn sal hierdie kruip noem, maar Angus is veel slimmer as ek en sekerlik so ook Leon en Brianvds, maar met die lees van die volgende twee artikels het ek dit 'gesave' op my Kindle en herhaal ek dit hier weens die gesprek wat deur Jan Rap afgeskop is en het ek met die aanvanklike lees daarvan nogal gedink aan Angus en die wat die tegniese beter as ek verstaan.

Dit word daarom in detail geplaas en verdiep dit die debat sonder enige twyfel

Baie dankie

Wouter

Skull Fossil Suggests Simpler Human Lineage (Hierdie dink ek kom uit die NYT)

By JOHN NOBLE WILFORD

After eight years spent studying a 1.8-million-year-old skull uncovered in the Republic of Georgia, scientists have made a discovery that may rewrite the evolutionary history of our human genus Homo.

It would be a simpler story with fewer ancestral species. Early, diverse fossils — those currently recognized as coming from distinct species like Homo habilis, Homo erectus and others — may actually represent variation among members of a single, evolving lineage.

In other words, just as people look different from one another today, so did early hominids look different from one another, and the dissimilarity of the bones they left behind may have fooled scientists into thinking they came from different species.

This was the conclusion reached by an international team of scientists led by David Lordkipanidze, a paleoanthropologist at the Georgian National Museum in Tbilisi, as reported Thursday in the journal Science.

The key to this revelation was a cranium excavated in 2005 and known simply as Skull 5, which scientists described as “the world’s first completely preserved adult hominid skull” of such antiquity.

Unlike other Homo fossils, it had a number of primitive features: a long, apelike face, large teeth and a tiny braincase, about one-third the size of that of a modern human being.

This confirmed that, contrary to some conjecture, early hominids did not need big brains to make their way out of Africa.

The discovery of Skull 5 alongside the remains of four other hominids at Dmanisi, a site in Georgia rich in material of the earliest hominid travels into Eurasia, gave the scientists an opportunity to compare and contrast the physical traits of ancestors that apparently lived at the same location and around the same time.

Dr. Lordkipanidze and his colleagues said the differences between these fossils were no more pronounced than those between any given five modern humans or five chimpanzees. The hominids who left the fossils, they noted, were quite different from one another but still members of one species.

“Had the braincase and the face of Skull 5 been found as separate fossils at different sites in Africa, they might have been attributed to different species,” a co-author of the journal report, Christoph Zollikofer of the University of Zurich, said in a statement. Such was often the practice of researchers, using variations in traits to define new species.

Although the Dmanisi finds look quite different from one another, Dr. Zollikofer said, the hominids who left them were living at the same time and place, and “so could, in principle, represent a single population of a single species.”

He and his Zurich colleague, Marcia Ponce de León, conducted the comparative analysis of the Dmanisi specimens.

“Since we see a similar pattern and range of variation in the African fossil record,” Dr. Zollikofer continued, “it is sensible to assume that there was a single Homo species at that time in Africa.” Moreover, he added, “since the Dmanisi hominids are so similar to the African ones, we further assume that they both represent the same species.”

But what species?

Some team members simply call their finds “early Homo.” Others emphasized the strong similarities to Homo erectus, which lived between two million and less than one million years ago.

Tim D. White, a paleoanthropologist at the University of California, Berkeley, called it “the most primitive H. erectus yet known,” noting that “it is more similar than any other yet found to early Homo from eastern Africa,” a group of hominids estimated to have lived 2.3 million years ago.

All five of the skulls and skeletal bones were found in underground dens, suggesting grisly scenes from the perilous lives these early Homos led.

They resided among carnivores, including saber-toothed cats and an extinct giant cheetah.

All five of the individuals had probably been attacked and killed by the carnivores, their carcasses dragged into the dens for the after-hunt feast, with nothing left but dinner scraps for curious fossil hunters.

Dr. White and other scientists not involved in the research hailed the importance of the skull discovery and its implications for understanding early Homo evolution. In an article analyzing the report, Science quoted Ian Tattersall of the American Museum of Natural History in New York as saying that the skull “is undoubtedly one of the most important ever discovered.”

A few scientists quibbled that the skull looks more like Homo habilis or questioned the idea that fossils in Africa all belong to Homo erectus, but there was broad recognition that the new findings were a watershed in the study of evolution.

“As the most complete early Homo skull ever found,” Dr. White wrote in an e-mail, “it will become iconic for Dmanisi, for earliest Homo erectus and more broadly for how we became human.”

Dr. White, who has excavated hominid fossils in Ethiopia for years, said he was impressed with “the total evidentiary package from the site that is the really good news story here.” Further, he said, he hoped the discovery would “now focus the debate on evolutionary biology beyond the boring ‘lumpers vs. splitters' ” — a reference to the tendencies of fossil hunters to either lump new finds into existing species or split them off into new species.

In their report, the Dmanisi researchers said the Skull 5 individual “provides the first evidence that early Homo comprised adult individuals with small brains but body mass, stature and limb proportions reaching the lower range limit of modern variation.”

Skeletal bones associated with the five Dmanisi skulls show that these hominids were short in stature, but that their limbs enabled them to walk long distances as fully upright bipeds.

The shape of the small braincase distinguished them from the more primitive Australopithecus genus, which preceded Homo and lived for many centuries with Homo in Africa.

Christening the Earliest Members of Our Genus

By Carl Zimmer

(Hierdie indien korrek onthou kom van Zimmer se blog by Natgeo)

Around 1.8 million years ago, human evolution passed a milestone. Our ancestors before then were little more than bipedal apes. Those so-called hominids had chimpanzee-size bodies and brains, and they still had adaptations in their limbs for climbing trees. But the fossils of hominids from 1.8 to 1.5 million years ago are different. They had bigger brains, flatter faces and upright bodies better suited to walking.

Their geography changed, too.

While earlier hominid fossils have only been found in Africa, the newer ones also turn up at sites stretching across Asia, from the Republic of Georgia all the way to Indonesia.

These cosmopolitan hominids are so much like modern humans that paleoanthropologists consider them the earliest members of our own genus, Homo.

But they didn’t belong to our species, Homo sapiens. After all, their brains were still no more than two-thirds the size of our own, and they could only make simple hand axes and other crude stone tools.

But if not Homo sapiens, then Homo what?

What species did these fossils belong to?

That turns out to be a remarkably hard question to answer — in part because it is difficult to settle on what it means to be a species.

The first early Homo fossils were discovered in 1891 in Indonesia by Eugene DuBois.

They came to be known as Homo erectus, named for its erect stance. In later decades, scientists found other fossils in other places, and they often decided that the fossils were so different from anything found before that they must belong to a separate species.

Species names exploded: Homo erectus was joined by Homo ergaster, Homo georgicus, Homo rudolfensis and others.

But all those species were established based on only a modest numbers of fossils. And so some uncertainty is inevitable. Imagine that paleontologists from the distant future learned everything they knew about our entire species from the skeleton of a single NBA player. If they then uncovered the skeleton of a five-foot gymnast, they would be right to wonder whether they had found a separate species.

Last week, a team of scientists offered a rare glimpse of the diversity of early Homo fossils.

In the journal Science, they compared five gorgeously preserved, 1.8 million-year-old skulls from a site called Dmanisi in the Republic of Georgia.

In just one spot, they found a stunning diversity of forms.

One skull had a large jaw and a tiny brain less than half the size of a human one.

But some of their brains were up to 25 percent bigger than that specimen, while their jaws were much smaller.

Nevertheless, the scientists found a lot of underlying similarities in the skulls’ structures.

Their variation is no greater than that found in living species, like chimpanzees and humans.

“They don’t represent distinct species,” said G. Philip Rightmire of Harvard University, a co-author on the study. “They’re just one group.” Dr. Rightmire and his colleagues then compared the Dmanisi skulls to many of the early Homo skulls found across the Old World. All of those far-flung fossils fell within the same range of variation that the scientists found at Dmanisi.

Based on this analysis, the scientists declared that all those early Homo fossils belong to a single species — which they suggest should be called Homo erectus.

If other researchers find evidence to support this view, said Dr. Rightmire, it would have a big impact on how we understand human evolution.

“We’ll have to go back to drawing boards and rethink the origins of Homo right from the start,” he said.

If Homo erectus was indeed a single species, its range would have been tremendous compared with our closest living ape relatives. Chimpanzees, for example, live only across a narrow band of sub-Saharan Africa. What’s more, ape species tend to split apart into new ones.

Two million years ago, for example, a bend of the Congo River cut off the chimpanzees in the southern part of the species’s range. Those southern chimpanzees evolved into smaller, more slender apes that today are more peaceful than their warring cousins north of the river.

Their DNA reveals little sign that they have interbred with other chimpanzees over the past two million years — despite living within a few miles of them.

As a result, biologists have given them their own species name: Pan paniscus, commonly known as bonobos.

If Homo erectus was like chimpanzees, it would be remarkable for them to hang together across rivers and deserts and mountain ranges as a single species.

But Todd R. Disotell, a biological anthropologist at New York University, suggests that early Homo might be more like another primate.

“Baboons probably make a good analog,” said Dr. Disotell.

Baboons live across much of Africa, as well as the Middle East. From place to place, the baboons look different — so different, in fact, that scientists have split them into some half a dozen species. And if you look at their DNA, you can find evidence that these so-called species have remained distinct from each other for up to four million years.

These baboons have overlapping ranges, and where they come into contact, they regularly interbreed. They have hybrid babies that are perfectly healthy. Some genes from one group of baboons can spread into another this way. And yet the groups remain distinct, never blurring together.

Each group of baboons has adapted to one particular way of life — some surviving in a desert, for example, and others in a woodland. For the most part, the genes that help a baboon in one range put it at a disadvantage somewhere else. The baboon expert Clifford Jolly first proposed that our ancient relatives were joined together by a baboon-like web of connections. Distinct groups of hominids lived in distinct ranges.

But in some places, at some times, they came into contact with other hominids, and their biology allowed them to interbreed. “Maybe Dmanisi was the equivalent of that,” said Dr. Disotell.

While this explanation may turn out to be closer to the truth than the idea of a single species, it would leave us struggling to find the right name for our ancient relatives.

Was each one a separate species, deserving of its own name?

Dr. Disotell doubts we can answer that question, pointing to baboons. Despite a luxury of data, scientists continue to debate whether baboons belong to different species, or just one.

“What we need, practically, is labels for them,” said Dr. Disotell.

“We will never solve the species problem for fossils if we can’t for living, breathing animals.”

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Jan Rap

2013-11-04 at 17:44

Brianvds, 'veel steur' sou ek vervang met 'met 'n knippie sout' en dit geld nie alleen vir Popular Mechanics nie maar ook Nature, Scientific American, New Scientist en Dawkins se T-hemp

Reply

Jan Rap

2013-11-04 at 18:29

Beste Angus

Ek stem saam met jou dat mens geneig is om goed te aanvaar wat met jou mening strook en te verwerp die wat nie met jou mening strook nie. In my geval is dit beslis so, jy slaan die spyker op die kop maar die sleutelwoord is GENEIG, nie onteenseglik soos jy beweer nie.

Ek sê dan in my brief dit LYK vir my of Dawkins te vroeg gepraat het en NIE 'pê wê wê Dawkins is verkeerd' nie. Ek het nog bygevoeg ook dat die moontlikheid bestaan dat die navorsing wat aanleiding gegee het tot die beriggie in Popular Mechanics verkeerd kan wees. Het jy nie mooi gelees nie of wat?

Ek vat die Asiëstorie ook met 'n knippie sout - ek sê nog steeds die waarskynlikste is die mens is afgelaai hier, taal en al, destyds, sommige in Oos-Gondwana uit sê sterrestelsel A, ander in Wes-Gondwanaland uit sterrestelsel B en so aan, dalk ook nog in die destydse suide en noorde ook. En, veral wat jy weet, gaan die aflaaiery nog steeds voort.

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Dirk Rigter

2013-11-05 at 08:05

Touché, Angus.

Jou eerste paragraaf (reaksie) is 'n kolskoot! Ek sal dit vir baie lank onthou.

Dirk Rigter.

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CorneliusHenn

2013-11-05 at 08:37

... en Dirk Rigter het natuurlik nie 'n benul dat dit op hom (nes Angus self) ook van toepassing is nie!

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CorneliusHenn

2013-11-05 at 08:50

Hahahahahaha! ... Brianvds en Angus, ek sou julle veel eerder as intelligent beskryf! ... maar nou ja, die slimjanne raak eensaam en bied julle so tussen die oorweldigende spoeg en plak 'n rang as die slimste ... hahahahaha ... ek glo egter julle het genoeg wysheid en verstand om dit ook met 'n knippie sout te neem ... ek glo ook enige ander intelligente belangstellende sal weet dat gewoon dit onmoontlik is om gedurig dieselfde hoeveelheid en derduisende woorde in 'n teenargument te plak - daarom dat die slimjanne hul klug so maklik en kamstig die botoon voer!

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Jan Rap

2013-11-05 at 10:20

Dirk, dis wel raak maar nie 'n kolskoot nie want Angus impliseer dat ek nou die Popular Mechanics-beriggie as onteenseglik aanvaar wat nie die geval is nie. Om die waarheid te sê, ek aanvaar baie min dinge as onteenseglik waar (en laat ek dadelik erken dis meer uit hoofde van 'n gebrek aan kennis as kennis in pag. Die feit bly egter dat ek baie min dinge as onteenseglik waar beskou selfs al strook dit met wat ek in my water voel).
Waar dit wel 'n kolskoot is, is dat dit in jou geval geld soos blyk uit jou onthutsgeit wanneer iemand van jou ingeplante menings verskil.
Jan Rap

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Angus

2013-11-05 at 14:33

Nee, wat, Jan! Sulke semantiese geronddansery help niks. As ek vir iemand sê: "Kom lyk my gat reën," dan glo ek vas dat die water nou-nou gaan spat.

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Jan Rap

2013-11-06 at 16:07

Ag ou Angus, daar druk jy alweer jou kop in die sand. Jy't of half gelees en toe op die kassie geklim, of op die kassie geklim om aspris bietjie kreatief om te gaan met wat ek gesê het (en die een is so reg soos die ander). Hoe verberg mens die eier op jou gesig in so 'n situasie? Jy soek 'n hopie sand (in jou geval die beskuldiging van 'semantiese ronddansery') en verberg jou gesig. Dit help nie; almal het die eier gesien.

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Angus

2013-11-07 at 14:18

Beste Jan,

Ek twyfel of jy besef wat jy self geskryf het. Jy sê tog duidelik dat Dawkins sy T-hempies moet bêre totdat "bogenoemde navorsing" (dit is nou die "navorsing" wat in Poplular Mechanics gedoen is), totdat hierdie navorsing "verkeerd bewys" is. Met ander woorde jy beskou dit mos onteenseglik as meer aanvaarbaar as die Afrika-teorie.

As jy nou ook jou Poplular Mechanics-navorsing mooi lees, sal jy agterkom dat dit nie die Afrika-teorie weerspreek nie. Die Afrika-teorie het te make met die oorsprong van die Homo-spesie. Jou "navorsing" het te make met die oorsprong van die primaat wat weer op een of ander manier geëmigreer het sodat daar Afrika-primate is en ook Amerikaanse primate.

Dis eintlik 'n ingewikkelde storie wat nie sommer met een artikel in Poplular Mechanics weggevee kan word nie. En ek sou allermins sommer so links en regs eier-in-die-gesig-beskuldigings wil uitdeel.

Groete

Angus

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Jan Rap

2013-11-14 at 15:18

Angus
Wat is dit met jou en eiers want hier voer jy nou weer 'n eierdans uit:
Hierbo sê jy " ... en dit word nou vir hom onteenseglike bewys dat Homo sapiens sy ontstaan in Asië het.
Ek antwoord en sê onder andere " ...maar die sleutelwoord is GENEIG, nie onteenseglik soos jy beweer nie." Jou antwoord daarop is " ... Met ander woorde jy beskou dit mos onteenseglik as meer aanvaarbaar as die Afrika-teorie."
Kreatief (ek vermy die woord 'kul' want jy's my vriend wat 'n boek vir my gestuur het en njannies, die een wat ek vir jou stuur is jy kan maar sê op pad): Eers is dit onteenseglike bewys en nou's dit onteenseglik as meer aanvaarbaar.
Groetnis
Jan Rap

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F C Boot

2013-11-16 at 22:38

Lyk my dit word nou 'n geval van oud, ouer, oudste as jy die volgende artikel in aanmerking neem.

Brain shape Confirms Controversial fossil as oldest human ancestor.

Scientific American April 4 2013 HONOLULU–A seven-million-year-old skull found in the Djurab Desert in Chad may indeed represent the earliest known member of the human family. Researchers unveiled the specimen back in 2002 and made quite a splash with their claim that the ancient fossil was our ancestor.

They assigned it to a new species, Sahelanthropus tchadensis (nickname: Toumaï) and said it was very close to the point at which the human lineage diverged from that of our closest living relative, the chimpanzee. Critics, however, countered that the skull was probably an ape’s instead of that of a hominin (a creature on the line leading to us), given its primitive features.

But a new analysis of the skull—specifically, its braincase—supports the discoverers’ claim that Toumaï is a hominin. Thibaut Bienvenu of the Collège de France and his colleagues reconstructed Toumaï’s endocast—a cast of the interior of the braincase, which reveals the shape of the brain. Because the fossil skull is distorted and filled with a highly mineralized matrix, they had to do their reconstruction virtually, which meant imaging it with 3D X-ray synchrotron microtomography and then feeding that data into a program that allowed them to remove the matrix and correct the distortion on screen.

The resulting virtual reconstruction of the endocast reveals that Toumaï had a cranial capacity of 378 cubic centimeters—consistent with earlier estimates. This puts it within the range of chimp cranial capacity. In comparison, modern humans have brains around three times larger than that.

But though Toumaï’s brain was apelike in its small size, it was apparently homininlike in other ways. In a presentation given on April 2 at the annual meeting of the Paleoanthropology Society, Bienvenu reported that the endocast shows strongly posteriorly projecting occipital lobes, a tilted brainstem, and a laterally expanded prefrontal cortex, among other hominin brain characteristics.

Previously, Michel Brunet of the Collège de France, whose team discovered Toumaï*, and his colleagues argued that Toumaï was a hominin on the basis of traits including his relatively small canine teeth, which are associated with reduced aggression, and the forward position of his foramen magnum (the spinal cord opening in the base of the skull), which is associated with upright walking.

Both of these characteristics are considered hallmarks of humanity. But skeptics argued that other features, such as the hulking brow ridge and aspects of the rear and base of the skull, signaled that the fossil represents an ape.

The endocast traits bolster the original interpretation. Bienvenu said that Toumaï’s endocast offers “a unique window on the first stage of human brain evolution” and shows evidence of brain reorganization toward the human condition well before brain size had begun to expand. He added that this early brain reorganization was probably a consequence of the shift to upright walking.

04/10/13 Posted updated to identify Brunet.

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