SILAHKAN MENGGUNAKAN " MESIN TRANSLATE "..GOOGLE TRANSLATE
DISAMPING KANAN INI.............
PLEASE USE ........ "TRANSLATE MACHINE" .. GOOGLE TRANSLATE BESIDE RIGHT THIS
....................................
DISAMPING KANAN INI.............
PLEASE USE ........ "TRANSLATE MACHINE" .. GOOGLE TRANSLATE BESIDE RIGHT THIS
....................................
Tengkorak
dengan campuran Neanderthal dan ciri-ciri primitif menerangi evolusi manusia
Skulls with mix of Neandertal and primitive traits illuminate human
evolution
Date:
June 19,
2014
Source:
American Association for the
Advancement of Science
Summary:
Researchers have analyzed the largest collection of
ancient fossil hominin species ever recovered from a single excavation site,
shedding light on the origin and evolution of Neandertals.
.......................
Researchers studying a collection of skulls in a Spanish
cave identified both Neandertal-derived features and features associated with
more primitive humans in these bones. This "mosaic pattern" supports
a theory of Neandertal evolution that suggests Neandertals developed their
defining features separately, and at different times -- not all at once. Having
this new data from the Sima de los Huesos site, as the Spanish cave is called,
has allowed scientists to better understand hominin evolution during the Middle
Pleistocene, a period in which the path of hominin evolution has been
controversial.
"The
Middle Pleistocene was a long period of about half a million years during which
hominin evolution didn't proceed through a slow process of change with just one
kind of hominin quietly evolving towards the classic Neandertal," said
lead author Juan-Luis Arsuaga, Professor of Paleontology at the Complutense
University of Madrid.
"With
the skulls we found," co-author Ignacio Martínez, Professor of
Paleontology at the University of Alcalá, added, "it was possible to
characterize the cranial morphology of a human population of the European Middle
Pleistocene for the first time."
About 400 to
500 thousand years ago, in the heart of the Pleistocene, archaic humans split
off from other groups of that period living in Africa and East Asia, ultimately
settling in Eurasia, where they evolved characteristics that would come to
define the Neandertal lineage. Several hundred thousand years after that,
modern humans -- who had evolved in Africa -- settled in Eurasia, too. They
interbred with Neandertals, but even then showed signs of reproductive incompatibility.
Because of this, modern humans eventually replaced Neandertals.
The degree
of divergence between Neandertals and modern humans over such a short period of
time has surprised scientists. Why did Neandertals differentiate so quickly
from other early hominins? What pattern of changes did Neandertals undergo?
To answer
these questions, scientists have needed an accurate picture of European
populations around 400,000 years ago, the early stages of the Neandertal
lineage. This has been challenging, however, because the European fossil record
-- an important tool for answering these questions -- is isolated and
dispersed, consisting of remains from disparate timelines. Samples at the Sima
de los Huesos site in Atapuerca, Spain, however, are different.
"What makes
the Sima de los Huesos site unique," Arsuaga said, "is the
extraordinary and unprecedented accumulation of hominin fossils there; nothing
quite so big has ever been discovered for any extinct hominin species --
including Neanderthals."
"This
site has been excavated continuously since 1984," Martínez added.
"After thirty years, we have recovered nearly 7,000 human fossils
corresponding to all skeletal regions of at least 28 individuals. This
extraordinary collection includes 17 fragmentary skulls, many of which are very
complete."
The 17
skulls belong to a single population of a fossil hominin species. Some of have
been studied before, but seven are presented anew here, and six are more
complete than ever before. With these intact samples at their fingertips, the
researchers made progress characterizing defining features.
Their work
has helped address hypotheses about Neandertal evolution, specifically the
accretion model hypothesis, which suggests that Neandertals evolved their
defining features at different times, not in a single linear sweep.
"For
decades the nature of the evolutionary process that gave rise to Neanderthals
has been discussed," explained Martínez. "An important question in
these debates was whether the 'neandertalization process' involved all regions
of the skull from the beginning, or if, on the contrary, there were various
stages in this process that affected different parts of the skull at different
times."
The
researchers' skull samples showed Neandertal features present in the face and
teeth, but not elsewhere; the nearby braincase, for example, still showed
features associated with more primitive hominins.
"We
think based on the morphology that the Sima people were part of the Neanderthal
clade," Arsuaga said, "although not necessarily direct ancestors to
the classic Neanderthals." They were part of an early European lineage
that includes Neanderthals, but is more primitive than the later Pleistocene
variety.
Critically,
many of the Neandertal-derived features the researchers observed were related
to mastication, or chewing. "It seems these modifications had to do with
an intensive use of the frontal teeth," Arsuaga said. "The incisors
show a great wear as if they had been used as a 'third hand," typical of
Neanderthals."
The work of
Arsuaga et al. suggests that facial modification was the first step in
Neandertal evolution. This mosaic pattern fits the prediction of the accretion
model.
"One
thing that surprised me about the skulls we analyzed," Arsuaga said,
"is how similar the different individuals were. The other fossils of the
same geological period are different and don´t fit in the Sima pattern. This
means that there was a lot of diversity among different populations in the
Middle Pleistocene."
Indeed,
other European Middle Pleistocene Homo sapiens do not exhibit the suite
of Neandertal-derived features seen in this fossil group. Thus, more than one
evolutionary lineage appears to have coexisted during the European Middle
Pleistocene, with that represented by the Sima sample being closer to the
Neandertals.
Arsuaga and
his team were delighted to work on this effort. "Finding a single tooth is
a great success in any other site of comparable age, so imagine what it is like
to painstakingly reconstruct 17 skulls," he said. "It's like finding
a treasure."
Story
Source:
The above
story is based on materials provided by American Association for the Advancement of Science. Note: Materials may be edited
for content and length.
Journal
Reference:
- J. L. Arsuaga, I. Martínez, L. J. Arnold, A. Aranburu, A. Gracia-Téllez, W. D. Sharp, R. M. Quam, C. Falguères, A. Pantoja-Pérez, J. Bischoff, E. Poza-Rey, J. M. Parés, J. M. Carretero, M. Demuro, C. Lorenzo, N. Sala, M. Martinón-Torres, N. García, A. Alcázar de Velasco, G. Cuenca-Bescós, A. Gómez-Olivencia, D. Moreno, A. Pablos, C.-C. Shen, L. Rodríguez, A. I. Ortega, R. García, A. Bonmatí, J. M. Bermúdez de Castro, and E. Carbonell. Neandertal roots: Cranial and chronological evidence from Sima de los Huesos. Science, 2014; Vol. 344, no. 6190, pp. 1358-1363 DOI: 10.1126/science.1253958