De "Hobbit"

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De "Hobbit"

Bericht  Grendel op wo 11 feb 2009, 20:53

Sibbevader schreef:'Hobbit' stirs scientific clash

By Paul Rincon



A US-British team of scientists has challenged the idea that the tiny
skeleton from Indonesia dubbed the "Hobbit" is a new human species.



Writing in Science magazine, the team presents an alternative
theory that the remains could be those of a modern human with a brain
disorder.



Their arguments appear in a technical critique of previous research into the Hobbit brain also published in Science.



But the authors of that earlier paper have vigorously defended their work.



The skeletal remains were discovered by an Australian-Indonesian
research team in the cave of Liang Bua on the island of Flores in 2003.



After carefully analysing the bones, the group declared them to be
those of a human species previously unknown to science, and to which
they gave the classification Homo floresiensis . (The specimen is also
sometimes referred to as LB1 after the cave in which it was found).



'Sensational' find



The creature stood just 1m (3ft) tall and possessed a brain size of
around 400 cubic centimetres (24 cubic inches) - about the same as a
chimp's brain. Dating of the sediments around the remains indicated the
Hobbit lived only 18,000 years ago.



LB1 caused a sensation when it was unveiled to the public through a publication in the academic journal Nature.



There is a fundamental problem of the tiny brain size combined with the sophisticated stone tools

Robert Martin, The Field Museum

A subsequent study published in Science in Grasmaand (Grasmaand (apr.)) 2005
focussed on LB1's brain. A team led by Professor Dean Falk, of Florida
State University in Tallahassee, compared a cast taken from the inside
of the braincase with other similar casts from primitive and modern
humans, including one individual with the condition microcephaly.



This disorder is characterised by a small brain and is sometimes associated with other defects.



Professor Falk's data supported the idea that LB1 was not a modern human but a creature new to science.



Now, biologist Robert Martin, of The Field Museum in Chicago, and
colleagues have questioned this conclusion. They presented some of
their arguments in a BBC documentary last year, but the Science paper
represents the team's formal technical position.



"There is a fundamental problem of the tiny brain size combined
with the sophisticated stone tools," Dr Martin told the BBC News
website.



Scaling rule



Some of the tools found with LB1 are of types previously only associated with modern humans ( Homo sapiens ).



Dr Martin also invokes a biological rule of scaling to argue that
LB1 could not have been a dwarfed version of the older human species
Homo erectus , as has been suggested.



The Martin team's concerns were raised in a BBC documentary

H. erectus is known to have lived on nearby Java, and one theory
proposed that a population of this species could have settled on Flores
and evolved a small stature. This can happen in remote, isolated
habitats, as organisms adapt to a scarcity of resources. The scaling
rule is based on known instances of so-called insular dwarfing in
mammals.



But these studies show that a reduction in body size is accompanied
only by a comparatively modest reduction in brain size. Dr Martin and
his colleagues argue that the brain of LB1 is far too small to be a
dwarf hominid, or human-like species.



Dr Martin used the scaling law to get to a brain size of 400 cubic
centimetres using H. erectus as the starting point. The scaling law
predicts a creature only 0.3m (1ft) tall and 2kg (4.4lbs) in
weight.law.



However, Professor Falk questioned whether basing a calculation of
dwarfing in a hominid on an example of dwarfing in an elephant - one of
the models used by Dr Martin in his analysis - was appropriate.



Wider picture



According to one theory, LB1's ancestor was not H. erectus at all,
but a smaller, ancestral hominid such as H. habilis ; or
Australopithecus , an even more ancient form. Some think this could
explain the small brain of H. floresiensis without breaking the scaling



Chris Stringer, head of human origins at the Natural History Museum,
UK, commented: "There are some interesting issues such as scaling of
the brain and whether a human could have as small a brain normally as
this creature seems to have.







It seems to be a primitive human - one that's distinct from anything we've found so far

Chris Stringer, Natural History Museum

"But if you look at the bigger picture, there are two jawbones and
remains from the rest of the skeleton from several other individuals."



He told the BBC News website: "When we look at the rest of the
material, including the post-cranial bones, we're finding this is a
strange kind of human. It doesn't seem to be a modern, pathological
individual. It seems to be a primitive human - one that's distinct from
anything we've found so far."



Professor Stringer pointed to the form of the shoulder blade and
the thick, chinless jawbones as particularly indicative that
researchers were dealing with a novel human species.



"Some of the material [at Liang Bua] is believed to go back to
70,000 years and the most recent material to 12,000 years. We're not
talking about one individual at one point in time. This morphology is
represented over a considerable period in time," he said.









Dr Martin also challenges Professor Falk's comparison of the adult
LB1 with a specimen from a 10-year-old microcephalic. He contends the
Indonesian example should have been matched against individuals with a
mild form of microcephaly that permitted survival into adulthood.



The Field Museum researcher provides his own microcephalic
specimens by way of comparison. But in their response, Dr Falk and
colleagues described Dr Martin's comparison as "inadequate" and lacking
"crucial details".

http://news.bbc.co.uk/go/pr/fr/-/1/hi/sci/tech/4994054.stm

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Re: De "Hobbit"

Bericht  Grendel op wo 11 feb 2009, 20:53

Sibbevader schreef:Indonesische `hobbit’ is nieuwe mensensoort



HASSELT - De menselijke soort heeft er een nieuwe - zij het
uitgestorven - tak bij: de Homo florensis. Uit recent onderzoek, nu
gepubliceerd in de ‘Proceedings of the Academy of Natural Sciences’,
blijkt dat de dwergskeletten die in 2003 op het Indonesische eiland
Flores gevonden werden een aparte mensensoort vertegenwoordigen.



Aanvankelijk werd nog gedacht dat de skeletten eigenlijk
dwergvarianten waren van de Homo sapiens - van ‘ons’, dus.
Dwergvarianten met een handicap, overigens, want de skeletten
vertoonden allen tekenen van micro-encefalie: een zo kleine hersenpan
dat ze er wel een mentale beperking aan over moesten houden.



In totaal vonden onderzoekers 9 skeletten in de Liang Bua-grot op
het Indonesische Flores, waarvan één vrijwel volledig. De individuen
waren zo’n 90 centimeter groot, wat hen de bijnaam ‘hobbits’ opleverde.
Volgens onderzoekers van de Universiteit van Florida waren die hobbits
echter niét mentaal gehandicapt. Ze vermoeden dat deze mensensoort zo
klein was omdat ze op den duur haar lichaamsbouw aanpaste aan de
schaarse voedselvoorraden op het eiland Flores. Dat leidde onder andere
tot een hersenpan met een inhoud van niet meer dan 400 kubieke cm,
ongeveer even veel als bij chimpansees.



Grondige analyse van die hersenpannen toont nu aan dat de hersensen
van deze ‘hobbits’ weliswaar kleiner waren, maar toch complex genoeg om
cognitieve taken uit te voeren. Deze hobbits waren dus geen
gehandicapte mensen, maar volwaardige individuen van een nieuwe soort.
Dat zou ook verklaren waarom er gesofisticeerde werktuigen en sporen
van een aangelegd vuur in de buurt van de skeletten werden gevonden.



Onderzoekers vermoeden nu dat de ‘hobbits’ van Flores afstamden van
een mogelijk aan de Homo habilis verwante, onbekende tak van de
menselijke familie. Die zou zijn uitgestorven toen Flores 12.000 jaar
geleden verwoest werd door een grote vulkaanuitbarsting.

Bron: http://www.steentijd.be
avatar
Grendel
Erfwacht

Man Aantal berichten : 1896
Woonplaats : Turholt
Registration date : 02-02-09

Profiel bekijken http://www.hagal.nl

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