麻豆传媒

THE BONES looked distinctly odd. Unearthed in 1856 by workers at a limestone
quarry in the Neander Valley near D眉sseldorf, they were strangely curved
and thick, and clearly very old. But their significance was far from obvious
even to the scientists who examined them. Many accepted the theory that they
belonged to a deformed Cossack horseman who had crawled into a cave to die.
Then, three years later, Charles Darwin published his ideas, and sparked a
debate about human origins. People began to see that our own evolutionary
history might be traced in the fossil record, and 鈥淣eanderthal Man鈥� was hailed
as the first European.

Today we know that Neanderthals dominated Europe and parts of Asia for around
200 000 years. They had large brains鈥攂igger than ours鈥攁nd they made
stone tools, cared for their injured and buried their dead. If a human life span
is 70 years, Neanderthals died out only a few hundred lifetimes ago. But time
has been hard on the Neanderthals. In popular culture they have become
synonymous with stupidity and a lack of sophistication, and most
palaeoanthropologists dismiss the old claim that they are our ancestors. Current
thinking centres on the 鈥淥ut of Africa鈥� theory: the idea that all modern humans
can trace their origins to a single African population whose descendants,
Cro-Magnons, spread across Europe some 40 000 years ago, killing off the
Neanderthals. 鈥淚 think the issue is resolved,鈥� says Richard Klein from Stanford
University. 鈥淵ou could always imagine how the case could be stronger. But if you
accept what I think are reasonable rules of evidence, then the story is
finished鈥攖he Neanderthals became extinct.鈥�

There are, however, some prominent dissenters from this view. They argue that
Neanderthals were not replaced, but absorbed through centuries of interbreeding
with the larger Cro-Magnon population. The 鈥淣eanderthals are us鈥� school of
thought was given a huge boost recently by evidence that Neanderthal populations
existed in both eastern and western Europe long after modern humans arrived, and
by the discovery in Portugal of what looks like the skeleton of a hybrid
child.

Alongside these findings has come a renewed focus on some tantalising clues
in the archaeological record suggesting that Neanderthals were capable of
surprisingly 鈥渕odern鈥� behaviours. Even researchers who do not consider
Neanderthals to be among our ancestors are starting to acknowledge that
interactions between Neanderthals and Cro-Magnons may have been more varied,
protracted and complex than they had thought. 鈥淭he supposed behavioural gap
between them and us has narrowed,鈥� says Chris Stringer of the Natural History
Museum in London, who originated the Out of Africa theory. 鈥淭his, together with
an apparently long period of coexistence in Europe, makes a simple scenario of
massive cognitive or technological superiority of [Cro-Magnon] much less
辫濒补耻蝉颈产濒别.鈥�

The current reappraisal of Neanderthals comes only two years after a group of
European and American scientists appeared to place them firmly on a dead-end
branch of the hominid family tree. They recovered and sequenced a small piece of
mitochondrial DNA from the original Neander Valley specimen, and found that the
difference between the Neanderthal sequence and an equivalent stretch of modern
DNA was three times greater than that between most modern populations. They
concluded that Neanderthals were a distinct biological species.

But enthusiasm for the DNA results has waned. 鈥淣o matter who you sample from
before 30 000 years ago, there鈥檚 a pretty good chance that their mitochondrial
DNA wouldn鈥檛 look like that of anybody alive today,鈥� says Klein. Others are even
more sceptical. Milford Wolpoff of the University of Michigan, who is a critic
of the idea that we are descended from a single population of early humans, says
of the DNA finding: 鈥淚t didn鈥檛 show that Neanderthals were a separate species,
only that they were more different from us than most contemporary human groups
are from each other.鈥�

Wolpoff鈥檚 student John Hawkes has developed a computer model that simulates
contemporary DNA patterns that might be expected under a range of evolutionary
scenarios, involving various degrees of interaction between Neanderthals and
Cro-Magnons. 鈥淲e should not expect to find Neanderthal mitochondrial DNA
lineages still around today,鈥� he concludes, 鈥渆ven in the case that they were
partly ancestral to living people in Europe and elsewhere.鈥�

Millennia of mutations

Wolpoff adds that a comparison between contemporary human and Cro-Magnon DNA
might also reveal large differences, due to mutations and other genetic changes
over the past 40 000 years. Such a comparison will require the sequencing of
more ancient DNA, a task that is proving extraordinarily difficult.

More direct evidence for interbreeding comes from the skeleton discovered in
Portugal last year. The bones, from a four-year-old boy, provide a clear
indication of hybridisation between Neanderthals and Cro-Magnons, according to
Jo茫o Zilh茫o, director of the Institute of Archaeology at the
University of Lisbon, and Erik Trinkaus of Washington University in St Louis,
Missouri. Their preliminary analysis has revealed a mix of anatomical features,
including a characteristically modern chin and teeth of Cro-Magnon, together
with robust Neanderthal limbs. From the evidence so far, hybridisation 鈥渟eems to
be the best possible explanation鈥�, says Zilh茫o. 鈥淚t鈥檚 as certain as any
new scientific hypothesis can be.鈥�

Perhaps the most intriguing aspect of the discovery is the radiocarbon date
from four separate samples of bone and charcoal from the grave site. The child
lived 24 500 years ago鈥攕everal thousand years after the last Neanderthal
populations are thought to have disappeared. 鈥淭he fact that 4000 years later
this mosaic of features is still present suggests that hybridisation a few
millennia before must have been extensive,鈥� says Zilh茫o.

But Stringer cautions against reading too much into this one discovery. 鈥淚f
the skeleton is that of a hybrid, it [still] cannot answer the questions of how
common such matings were, whether hybrids were fertile and whether their genes
ever penetrated into early modern populations,鈥� he says. And despite recent
revelations, the DNA evidence still suggests that interbreeding cannot have been
widespread. 鈥淭he evidence does fit with Neanderthals representing a deep and
separate lineage to that of all modern humans,鈥� he says.

In other parts of Europe, human fossils from this period generally show more
fully developed modern characteristics. Even so, the Portuguese boy may not be a
one-off example of hybridisation. Over the years, several sites have yielded
human remains鈥攎ostly fragmentary鈥攚hich, to some observers at least,
seem to have hybrid or transitional characteristics.

Until now, the strongest evidence has come from the work of David Frayer of
the University of Kansas. In a comparative analysis of fossils from various
sites in central and eastern Europe, Frayer has found what he says is convincing
evidence of biological continuity. His work focuses mainly on detailed features
of Neanderthal teeth and jaws, which he says show that 鈥渁 number of traits
present in Neanderthals were also present in the peoples who followed them. It
tells us there was gene flow . . . and refutes the argument of total
谤别辫濒补肠别尘别苍迟.鈥�

New chronologies indicate that there may have been plenty of time for
interbreeding to occur. Many anthropologists now accept that there were
Neanderthal outposts in Portugal and southern Spain as recently as 30 000 years
ago. At Zafarraya in southern Spain, for example, it appears that Neanderthals
were still around up to 8000 years after the arrival of Cro-Magnons in northern
Spain.

More surprising news came in March, when Paul Pettitt from the University of
Oxford revealed that Neanderthal fossil remains from the Vindija cave in Croatia
have been dated to 29 000 years ago. 鈥淭hese are the youngest dates we have for
any Neanderthals,鈥� says Fred Smith, an anthropologist from Northern Illinois
University who worked on the dating project with Pettitt and Trinkaus. 鈥淵ou
begin to wonder if modern humans were coming into Europe as early as we
thought,鈥� Smith adds. Trinkaus points out the parallel between these new dates
and those from Portugal and Spain. 鈥淲hat these late survivals emphasise more
than anything else is that the Out of Africa models are grossly simplistic,鈥� he
says.

These suggestions of side-by-side coexistence of modern and Neanderthal
populations over thousands of years are something of a problem for those who
still believe that the newcomers quickly drove Neanderthals to extinction. The
evidence from Spain, for example, points to a stable, long-term cultural
frontier along the valley of the River Ebro, with moderns in the north and
Neanderthals in the south. But if modern humans鈥� technological advantage was
such that they could replace the original inhabitants of most of Europe, why did
it not extend into the south of the Iberian peninsula?

Some anthropologists argue that Neanderthals and moderns may have each been
better adapted to conditions in different regions. 鈥淎s the climates regularly
changed . . . there would have been constant ebbs and flows in both populations,
with the Neanderthals gradually losing out,鈥� says Stringer. Zilh茫o notes
that a climatic threshold may have been reached around 30 000 years ago, with
cooler conditions鈥攖o which modern humans may have been better culturally
adapted鈥攕preading into the southernmost regions of Europe.

Another idea is that contact came late to Portugal and Spain because of their
isolated geographical position. But the same cannot be said of Croatia. 鈥淚t鈥檚 on
the pathway to the Near East,鈥� notes Smith, referring to the route by which
modern humans are thought to have spread into Europe.

While some fossil and DNA analysis hints at interbreeding, tools and other
artefacts provide evidence of sophisticated cultural production by
Neanderthals, during and even before the period of contact with Cro-Magnons.
According to conventional archaeology, the arrival of modern humans in Europe is
heralded by the appearance of new, more sophisticated stone and bone tools, and
by a rapid increase in symbolic representation in the form of portable and cave
art. In western Europe, early evidence of this 鈥渕odern鈥� Upper Palaeolithic
culture, known as the Aurignacian, dates back to around 38 000 years ago. The
fact that these assemblages often directly overlie Neanderthal fossil and
cultural remains has led to the hypothesis that a broad, east-to-west invasion
of competitively superior Cro-Magnons caused the Neanderthals鈥� demise.

Some archaeologists, such as Geoffrey Clark of Arizona State University and
Lawrence Straus of the University of New Mexico, have long disputed this view.
They interpret the evidence as revealing a continuum of change across the Middle
and Upper Palaeolithic, particularly the period between 40 000 and 30 000 years
ago. 鈥淚鈥檝e always argued that the transition is a mosaic, not a 20th-century-style
invasion,鈥� says Straus. 鈥淭he archaeological picture is of pockets
of different industries existing contemporaneously with each other. Some things
change quickly, some things don鈥檛鈥攊t depends on where you are in
贰耻谤辞辫别.鈥�

Straus says that the new evidence of overlap and interbreeding is consistent
with the variability found in the archaeological record. The late Neanderthal
remains at Vindija cave, for example, were found alongside several
Aurignacian-style stone and bone artefacts, as well as more typical Neanderthal
tools. Elsewhere in Europe, the picture is even more complex where different
cultural traditions鈥攏either Aurignacian nor typically
Neanderthal鈥攈ave been identified. Most famous is the Ch芒telperronian
culture known from some two dozen sites in France and northern Spain.
Ch芒telperronian artefacts include carefully crafted bone implements and
portable art objects. These items were once thought to be the hallmark of a
modern Upper Palaeolithic culture, but fossils from Saint-C茅saire and
Arcy-sur-Cure in France indicate that they were almost certainly produced by
Neanderthals. 鈥淚 think that the Ch芒telperronian is a big problem,鈥� says
Klein, 鈥渁nd I don鈥檛 have an explanation for it.鈥�

One possibility is that Neanderthals were merely imitating modern humans they
had seen, or were collecting their discarded artefacts. But this idea was
rejected in a controversial paper published last year by Zilh茫o and a
group of researchers led by Francesco d鈥橢rrico of the University of Bordeaux.
D鈥橢rrico鈥檚 team compared Ch芒telperronian ornaments and bone tools from
Arcy-sur-Cure with Aurignacian artefacts from the same site. They found a
distinct stylistic difference between the two, as well as differences in
production techniques, indicating that the Ch芒telperronian objects were
not the result of imitation. Moreover, says d鈥橢rrico, close scrutiny of the Arcy
record reveals that the Ch芒telperronian implements and the by-products of
their production were always found in strata below those containing Aurignacian
remains.

All this evidence indicates that the Ch芒telperronian predates the
arrival of Cro-Magnons and thus could only have been an independent invention by
Neanderthals. 鈥淭he Ch芒telperronian reveals that Neanderthals were fully
cultural human beings, with symbol-aided communication,鈥� says Zilh茫o.
This view is supported by evidence from other locations, including Croatia and
Italy. 鈥淲hen they arrived in Europe, moderns met Neanderthal populations that
had already accomplished their own Middle-to-Upper Palaeolithic transition.鈥�
Ultimately, he says, these Neanderthals were absorbed by anatomically modern
populations.

Critics argue that it seems rather too much of a coincidence for Neanderthals
to have achieved these modern behaviours immediately before the arrival of
modern peoples. But is it not equally a coincidence, replies d鈥橢rrico, that
artistic production by Cro-Magnons appears to flourish only when they enter
Europe and come in contact with Neanderthals?

Others go even further, and question whether the Aurignacian itself was
really the product of a distinct group of early human immigrants to Europe.
鈥淭here is no correlation whatsoever between particular `kinds鈥� of hominids and
particular `kinds鈥� of archaeological assemblages, either in Europe or anywhere
else,鈥� says Clark. And several researchers stress that the only clearly
identifiable hominid fossils from early Aurignacian times are
Neanderthal鈥攚hich certainly leaves room for speculation.

In a recent article in Science, Clark argued that our understanding
of modern human origins has been hampered by biases and assumptions inherent in
the different research traditions involved. 鈥淲e are in effect consumers of one
another鈥檚 research conclusions, but we pick and choose among them according to
our preconceptions,鈥� he wrote. Those preconceptions are shaped by 19th-century
cultural and taxonomic categories, says Clark, and he believes this
makes it difficult for researchers to appreciate the full extent of variation in
the archaeological and fossil record.

Stringer agrees that matching the archaeological record with fossil and
genetic evidence is tricky. But the combination of approaches should be a source
of strength rather than endless debate, he says. 鈥淚n the end there was only one
real history . . . and ultimately the different approaches should converge on
迟丑颈蝉.鈥�