Neanderthal culture: Old masters

   

The earliest known cave paintings fuel arguments about whether Neanderthals were the mental equals of modern humans.

Tim Appenzeller

In a damp Spanish cave, Alistair Pike applies a small grinder to the world's oldest known paintings. Every few minutes, the dentist-drill sound stops and Pike, an archaeologist from the University of Southampton, UK, stands aside so that a party of tourists can admire the simple artwork — hazy red disks, stencilled handprints, the outlines of bison — daubed on the cave wall tens of thousands of years ago. He hopes that the visitors won't notice the small scuff marks he has left.
In fact, Pike's grinder — and the scalpel that he wields to scrape off tiny samples — is doing no harm to the actual paintings, and he is working with the full approval of the Spanish authorities. Pike is after the crust of calcite that has built up over the millennia from groundwater dripping down the wall. The white flecks that he dislodges hold a smattering of uranium atoms, whose decay acts as a radioactive clock. A clock that has been ticking ever since the calcite formed on top of the art.

 

The results of an earlier round of sampling in El Castillo cave, published last June¹, showed that the oldest of the paintings, a simple red spot, dates to at least 40,800 years ago, roughly when the first modern humans reached western Europe. Pike and his colleagues think that when they analyse the latest samples, the paintings may turn out to be older still, perhaps by thousands of years — too old to have been made by modern humans. If so, the artists must have been Neanderthals, the brawny, archaic people who were already living in Europe.

The answer won't be known for at least a year, but if it favours the Neanderthals, it could tip — if not resolve — a debate that has rumbled for decades: did the Neanderthals, once caricatured as brute cavemen, have minds like our own, capable of abstract thinking, symbolism and even art? It is one of the most haunting questions about the people who once shared a continent with us, then mysteriously vanished.
An early date for the paintings would also be a vindication for the slight, dark-haired man watching as Pike works: João Zilhão, who has emerged as the leading advocate for Neanderthals, relentlessly pressing the case that these ice-age Europeans were our cognitive equals. Zilhão, an archaeologist at the Catalan Institution for Research and Advanced Studies at the University of Barcelona in Spain, believes that other signs of sophisticated Neanderthal culture have already proved his point. But he is willing to debate on his opponents' terms. “To my mind, we don't need that evidence,” he says of the paintings. “But I guess for many of my colleagues this would be the smoking gun.”
The front line in the Neanderthal wars runs through another cave: Grotte du Renne, 1,000 kilometres away in central France. As early as the 1950s, excavations there unearthed a collection of puzzling artefacts. Among them were bone awls, distinctive stone blades and palaeolithic baubles — the teeth of animals such as foxes or marmots, grooved or pierced so that they could be worn on a string. They were buried beneath artefacts typical of the first modern humans in Europe, suggesting that these objects were older. A startling possibility loomed: that artefacts of this style, collectively known as the Châtelperronian industry, were made by Neanderthals.

First appearance of Neanderthals in Europe

Neanderthals are thought to have originated in western Eurasia and migrated into Europe some time after 300,000 years ago.

Natural History Museum/Mary Evans

Close cousins of modern humans, Neanderthals evolved in western Eurasia and had Europe to themselves for more than 200,000 years, enduring several ice ages. In spite of their survival skills and big brains — comparable to our own — they had never been linked to sophisticated tools of this kind, or to ornaments. Yet in 1980, archaeologists reported finding a Neanderthal skeleton among Châtelperronian tools at another site in France². And in 1996, French palaeoanthropologist Jean-Jacques Hublin and his colleagues reported that a skull fragment from the ornament layer in the Grotte du Renne was unmistakably Neanderthal³.
Ever since then, the Grotte du Renne has been exhibit A in the case that Neanderthals, like ourselves, trafficked in symbols, using ornaments as badges of identity for individuals or groups.
Hublin himself did not go that far. He suggested that the Neanderthals had fallen under the spell of strange new neighbours: modern humans, who were thought to have reached Europe around the time of the Châtelperronian industry. Neanderthals might have acquired the ice-age bling from modern humans, or made the pendants themselves under the influence of the new arrivals.
That conclusion infuriated Zilhão, turning him into the passionate advocate he is today. He questioned the evidence that modern humans were already on the scene and detected a bias against our extinct cousins. “Why was the equally if not more legitimate hypothesis — that the Neanderthals themselves had been the authors of this stuff and made it for their own use — not even considered?” asks Zilhão.
On a visit to rock-art sites in Portugal, he discussed the paper with Francesco d'Errico, an archaeologist who is now at the University of Bordeaux in France. D'Errico had the same reaction, Zilhão recalls. “And he said: 'OK, let's do something about it.'” Since then, the pair has fought a two-front war, advancing evidence for Neanderthal capabilities while challenging studies that reserve symbolism and abstract thinking for modern humans.

Unknown artists

More than 15 years later, the Grotte du Renne continues to be a battleground. Since 2010, three papers have given duelling interpretations of the artefact-bearing layers. In the first, a group led by dating expert Thomas Higham of the University of Oxford, UK, used new carbon dates to argue that the layers were scrambled, mixing older remains with younger⁴. If that was correct, said Higham's team, the relics adjacent to the telltale skull fragment might not have belonged to Neanderthals after all.

Within months, Zilhão, d'Errico and their colleagues fired back with an analysis⁵ of how artefacts of different types were distributed in the Grotte du Renne, concluding that the layers were undisturbed and that the Neanderthal link could be trusted. A group led by Hublin (now at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany) presented its own dates last year, backing Zilhão's claim⁶. But Hublin still denied the Neanderthals full credit. Neanderthals did make the objects, now dated to between 45,000 and 40,000 years ago, he said — but only after they encountered modern humans. And this time he had fresh evidence to draw on.
Carbon dates measured by Higham and others at caves in Italy, Britain and Germany suggest that modern humans began expanding into Europe as early as 45,000 years ago, several thousand years earlier than was thought (see Nature 485, 27–29; 2012). Zilhão strenuously disputes those claims, doubting whether the shells or animal bones used for dating truly reflect the age of the human fossils at the sites, or whether the human remains are modern. “The evidence to show an early presence of modern humans in Europe is worse today than it was 20 years ago,” he declares.
Hublin, however, has no doubt that our ancestors had already entered the picture when Neanderthals in France began making bone awls and animal-tooth pendants. To assume that Neanderthals invented these technologies on their own is to accept “an incredible coincidence”, he says. “Just as modern humans arrive with these things in their pocket — bingo!”

Like minds

Despite the stalemate, Zilhão says that the record of Neanderthal behaviour tens of thousands of years before modern humans arrived in Europe proves his point (see 'Minds at work'). Neanderthals are believed to have buried their dead, suggesting that they had some kind of spirituality. They made glue for securing spear points by heating birch sap while protecting it from the air, a feat that even modern experimental archaeologists have trouble replicating. Many Neanderthal sites include lumps of pigment — red ochre and black manganese — that sometimes seem to be worn down like stone-age crayons. Zilhão and others think that the Neanderthals painted themselves, creating striking patterns on their pale, northern skin that were every bit as symbolic as the art and ornaments of modern humans.
“You don't need to have shell beads, you don't need to have artefacts with graphical representation to have behaviour that can be defined archaeologically as symbolic,” he says. “Burying your dead is symbolic behaviour. Making sophisticated chemical compounds in order to haft your stone tools implies a capacity to think in abstract ways, a capacity to plan ahead, that's fundamentally similar to ours.”
Where Zilhão sees a clear pattern, sceptics see uncertainties. Harold Dibble, an anthropologist at the University of Pennsylvania in Philadelphia, is re-examining supposed Neanderthal burial sites. At one, the French cave of Roc de Marsal, he says that what seemed to be a deliberately excavated grave is actually a natural pit. At another, La Ferrassie, he sees evidence that sediments swept into the cave by water — not grieving kin — could have buried Neanderthal remains.
As for the ochre crayons, Dibble is dismissive. “You see some wear on a piece of ochre and soon you've got Neanderthal body painting,” he says. “What a lot of logical leaps.” He and others say that the pigment has many possible uses: as an insect repellent, a preservative for food or animal skins, an ingredient in adhesives. Even Wil Roebroeks of the University of Leiden in the Netherlands, who found evidence for ochre use as early as 250,000 years ago at a Dutch Neanderthal site⁷, says that Zilhão “jumps too fast from the presence of ochre to body decoration”.
Ask Dibble, Hublin and other sceptics what would persuade them that Neanderthals had minds like ours, and their answer is simple: a pattern of art or other sophisticated symbolic expression from a time when no modern humans could possibly have been around. “But I don't think it exists,” says Hublin.
Zilhão, however, points to a singular finding from a Neanderthal site in southern Spain that he reported three years ago⁸: three cockle shells each with holes near one edge, as if they had been worn as ornaments. One contains a trace of red pigment, and a fourth shell is stained with a mixture of colours, as if it had been used as a paint container. The shells, says Zilhão, imply symbolic thinking fully equivalent to that of the modern humans who left troves of beads in South Africa 75,000 years ago. And at roughly 50,000 years old, he says, the Spanish shells date from a time well before modern humans reached the region.
Critics are not satisfied. The perforations are natural, as Zilhão himself noted, which suggests to Hublin and Dibble that rather than systematically fashioning ornaments, Neanderthals might have picked up a few odd shells on a whim. “When you've got isolated occurrences, one-offs, that's not going to convince most of us,” says Dibble.
The paintings in El Castillo could help to establish a pattern. The research group was conservative with the ages it reported last June¹, which put the earliest calcite at nearly 41,000 years old. Nervous about damaging the pigment, the team left several millimetres of the veneer intact at each sampled spot. Deeper, older layers might push back the paintings' minimum ages by several thousand years.
That prospect brought the team back to El Castillo last October. Grinding and scraping through a long day, the researchers concentrate on the red disks and hand stencils that had yielded the earliest dates last time around. The goal, says Zilhão, is “to date pigments in these paintings to an age that is clearly and to everyone's satisfaction beyond the range of modern humans in Europe”.
Yet an early date may not settle the long-running dispute. Hublin sets the bar high. “If Zilhão finds a date of earlier than 50,000 years ago, I'll be convinced!” he says. Any younger, and modern human influence would remain a possibility, he says, noting recent hints that our ancestors had advanced into Turkey or even central Europe by 50,000 years ago. And one example of crude painting — what Dibble calls “Neanderthal doodling” — might not be enough to win over the doubters. Zilhão's knockout blow may simply lead to more fighting.

Yet signs of a middle ground are emerging. Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, says that 20 years ago, he believed that if the Neanderthals made the Châtelperronian ornaments, they were blindly imitating modern humans. “Our interpretation was that they were copying but that they didn't have the brainpower to give full value” to the objects. He wouldn't say so now. Two decades of discoveries of sophisticated Neanderthal tools and weapons have made him think that “the gulf was not as great”: that the difference between Neanderthals and ourselves was a matter more of culture than of ability.
“You can see the Neanderthals were held back by various factors that were not down to their brains,” he adds. The climate of ice-age Europe kept their population size “frighteningly small”, he says — at times just a few thousand people across a whole continent, most of them dead by the age of 30. How could such a sparse, beleaguered people develop and sustain a sophisticated culture?
That's not so different from what d'Errico, Zilhão's comrade-in-arms for almost 20 years, now says. He still thinks that the Neanderthals probably invented the Châtelperronian artefacts before modern humans were on the scene. But he is open to the idea that aspects of modern human culture preceded their wholesale arrival in Europe. “It's possible that some influence did spread,” says d'Errico. “I'm less militant than João.” That takes nothing away from the Neanderthals, he adds. “The fact that Neanderthals can absorb influences, can re-elaborate them, can make them part of their own culture, is very modern behaviour.”
But there is a final stretch of ground that neither side will concede. Were the Neanderthals truly the same as us, cognitively? No, says Stringer. The Neanderthal genome, decoded⁹ in 2010, differs from that of modern humans in some regions linked to brain function, he notes. And this year, he suggested that, compared with modern humans, larger volumes of Neanderthals' brains were devoted to vision and to controlling their heavier bodies¹⁰ (see ‘Two kinds of human’). That might have left them with less capacity for social awareness and interaction. “If you imagine a Neanderthal in modern society, there would still be differences,” says Stringer.
Zilhão rejects any distinctions. Emerging from the cave into a rainy evening, he muses that if he pushes back the age of the El Castillo paintings, his critics may argue that he has simply proved an earlier presence of modern humans in Europe. “To which I will say, 'Of course. Neanderthals were modern humans too.'”

Nature

497,

302–304

(16 May 2013)

doi:10.1038/497302a

Biología cognitiva

Fundamentación en la mecánica cuántica y en la teoría de la información.

Alonso, Luis
Igual que aconteció con las fronteras de la física, en particular con la cuántica, las fronteras de la biología buscan planteamientos unificadores y tender puentes entre orillas que se creían irreconciliables. Así ocurre con el campo orgánico y el dominio de la cognición. El marco de esa aproximación lo pergeña la biología de sistemas. A través de la cognición, el organismo se muestra capacitado para habérselas con su entorno. Una actividad que, se supone, depende de la teoría de la información basada en probabilidades bayesianas.
El organismo se considera un sistema cibernético, un regulador de su propia homeostasis (el sistema metabólico) y un sistema selectivo que separa el yo del no-yo (la membrana en los organismos unicelulares). Todo organismo es un sistema complejo que puede sobrevivir solo si es capaz de mantener su orden interno frente a la tendencia espontánea hacia la disgregación. Por tanto, se ve obligado a seguir y controlar su entorno y, de ese modo, establecer circuitos de realimentación que resultan en una coadaptación. Los procesos cognitivos y los biológicos son inseparables. En la nueva disciplina, la neurociencia cognitiva se sitúa en su sustrato biológico. Mas, para buscar las bases biológicas de la cognición, hay que remitirse a la física y a la teoría de la información, ambos puntales profundamente conectados en la mecánica cuántica.
Detallada la naturaleza, adquisición y meditación de la información, se explicita esta en los principios generales de autoorganización y dinámica de los sistemas biológicos. Compete al lenguaje y la consciencia interpretar la información. Al cerebro se le considera soporte orgánico de la creación de inferencias a partir de la información de los sentidos, generador de predicciones y comprobador de hipótesis a través de su interacción con el mundo.
Se han realizado avances significativos en bioquímica y biología molecular. Pese a ello, parece cada vez más cierto que las metodologías reduccionistas tradicionales resultan insuficientes para abordar la complejidad de sistemas y problemas que van ocupando el centro de investigación. La exposición biológica y su lenguaje se han espejado en las explicaciones de la química y, en última instancia, de la física. Lo observamos en la búsqueda de una causalidad de los procesos. A los conceptos de masa, energía y fuerza, que a escala molecular y química implican fuerzas moleculares, concentración de determinadas sustancias químicas, velocidad de reacción, etcétera, hemos de añadir, cuando abordamos niveles superiores de organización biológica, los de fenómenos disipativos, temporización diferencial, procesos degenerativos y otros.
Por su lado, la ciencia cognitiva, joven disciplina creada con aportaciones de la psicología, neurología, teoría de redes neurales e inteligencia artificial, ha dado también pasos importantes en la conceptualización y el diseño de experimentos. El problema principal que atañe a la biología cognitiva es el de encontrar una mediación oportuna entre la teoría de la complejidad, importante para la biología, y el tratamiento mecánico-cuántico de la información, importante para la cognición. Ese nexo puede descubrirse en la noción de control de la información que tiende puentes entre procesos metabólicos y aspectos relativos a la información.
Cuando se abordan las relaciones entre física y biología, caben tres caminos posibles: apoyarse en la física clásica y la metodología reduccionista tradicional (buscar los fundamentos de la biología en conceptos y leyes de la física); rechazar cualquier nexo con la física para garantizar un fundamento autónomo para la biología; mostrar que la teoría física más revolucionaria, la mecánica cuántica, permite a la biología una conexión con la física que le faculta un fundamento autónomo sin violar las leyes de la física. Auletta sigue la tercera vía. Al afirmar que las ciencias biológicas, neurológicas o psicológicas deben reducirse a la física, se piensa en un reduccionismo ontológico a la física clásica (o la química clásica), como si estas constituyeran el paradigma definitivo de la ciencia. Pero el alcance de la física clásica (y la química clásica) ha quedado limitado a la resolución de determinados problemas. Ha ocupado su lugar, como explicación física del mundo, la mecánica cuántica.
En la búsqueda de nexos entre biología y mecánica cuántica se adelantaron Niels Bohr, Ernst Pascual Jordan, Max Delbrück y, sobre todo, Erwin Schrödinger. Andando el tiempo, Roger Penrose negaría que el cerebro funcionase como un ordenador clásico. En su opinión, el cerebro podía realizar cálculos aunque el problema no se hallara bien definido. La mecánica cuántica podría ser la solución de ese tratamiento anómalo de la información, una idea revolucionaria, aun cuando no se requiera que el cerebro se rija por las leyes de la física cuántica (en razón de la inmensa complejidad de su organización). Sabido es que las leyes cuánticas no regulan propiedades concretas de sistemas físicos, sino amplitudes de probabilidad. Del hecho de que la mecánica cuántica no regule sucesos concretos se infieren importantes consecuencias: queda margen para la aparición de nuevos tipos de sistemas físicos (imposible si el mundo estuviera regulado por las leyes de la mecánica clásica) y aporta condiciones necesarias para la aparición de la vida.
La física clásica se basaba en dos supuestos: todos los procesos y parámetros físicos relevantes son continuos (principio de continuidad) y todas las propiedades de un sistema físico están determinadas (principio de la determinación perfecta). Ambos supuestos fundamentales se violan en la mecánica cuántica: el principio de continuidad por el principio de cuantización y el supuesto de la determinación perfecta por el principio de superposición. Los sistemas mecánico-cuánticos, por elementales que sean, pueden considerarse fuente de información en nuestro mundo y procesadores de la misma.
La mecánica cuántica nos enseña que cada transmisión o adquisición de información será una combinación de un comportamiento discreto, local (selección de información) y de una conducta global, continua y ondulatoria. El cerebro es uno de esos sistemas clásicos que despliega ambos aspectos. Se caracteriza por dos fenómenos: la información se adquiere a modo de espigas, en términos discretos, mientras que la actividad global de procesamiento, en la que intervienen muchas neuronas o diversas áreas, presenta una forma ondulatoria. Durante siglos se pensó que el cerebro representaba el mundo externo de una forma pasiva, a la manera de imagen especular de los objetos y sus características; se reservaba para la mente el procesamiento lógico de la información así adquirida. En los últimos años ha ido ganando fuerza la tesis de que el cerebro interviene en el propio sesgo de la percepción, en su anticipación. De ese modo, vamos conociendo mejor las raíces biológicas de la cognición. La biología no es irrelevante para la cognición, ni esta, irrelevante para aquella.
Aunque arquetípico para hablar de información, el cerebro no es el único sistema biológico que se ocupa de la información. En los animales superiores encontramos tres sistemas que la tratan: el sistema sensorial periférico, los sistemas reguladores, en particular, el sistema hormonal, y el sistema nervioso central. Entre los vertebrados, compete al sistema sensorial adquirir información, procesarla y transmitirla al sistema nervioso central; el sistema hormonal regula la transmisión e intercambio de información; por fin, la función específica del sistema nervioso central consiste en adquirir información (procedente del sistema sensorial) y, en las áreas sensoriales y motoras, procesarla y controlar el intercambio de información. El sistema hormonal transmite información a través de las hormonas liberadas por las glándulas. En particular, regula los sistemas circulatorio, digestivo y reproductor, aparte de su influencia sobre el cerebro y el sistema nervioso central. La información del cerebro se transfiere también a través de la difusión local de moléculas neuroquímicas en una forma paracrina.
No existe isomorfismo entre el cerebro y los objetos externos, aun cuando, en un sentido más restringido, podemos hablar de cartografía topográfica y central. De acuerdo con la regla de Hebb, cuando un axón de una neurona participa reiteradamente en la excitación de otra neurona, se produce un proceso de desarrollo o cambio metabólico en una o ambas células, de suerte que pueden excitarse al alimón con alta probabilidad. Esta es la base teórica de la teoría conexionista de las redes neurales.

El libro impreso más antiguo del mundo.

 

Fue publicado hace 1.145 años y durante siglos permaneció oculto en una de las cuevas de Mogao, en China, hasta que lo descubrió el arqueólogo Aurel Stein

El 11 de mayo del año 868, hace 1.145 años, el chino Wang Jie autorizó la impresión y distribución de El sutra del diamante, el libro impreso más antiguo del que se tiene conocimiento, que se estampó casi 600 años antes que la Biblia de Gutenberg. El sutra del diamante no es el primer texto impreso de la historia, pero sí el más antiguo que se conserva hasta la fecha. El término «sutra» proviene del sánscrito, la antigua y sagrada lengua de la India, que es de origen indoeuropeo. Un sutra es un texto que recoge las palabras de Buda. Sus discípulos aprendían de memoria estos discursos y los transmitían de generación en generación. Al final de El sutra del diamante, Subhuti, un discípulo de Buda, le pregunta a éste cómo debería titularse el sermón, a lo que Buda le responde que deberá ser conocido como «El Diamante Cortador de Sabiduría Trascendental» porque «la enseñanza es fuerte y afilada como un diamante que corta a través de los malos enjuiciamientos y la ilusión».

La British Library conserva la copia

El texto original de El sutra del diamante, escrito en sánscrito, fue traducido al chino, alrededor del año 400, por un monje erudito indio llamado Kumarajiva. La copia china que se conserva, del año 868, fue hallada en 1907 por Aurel Stein (1862-1943), un arqueólogo húngaro-británico. Este precioso pergamino, de unos cinco metros de largo, había permanecido oculto, junto a otros 40.000 libros y manuscritos, en una cueva cercana a Dunhuang, una ciudad importante en la antigua Ruta de la Seda. La gruta forma parte de un conjunto sagrado de varios centenares de templos excavados en un precipicio arenoso, conocido como las cuevas de Mogao o las cuevas de los Mil Budas. Esta biblioteca secreta fue sellada alrededor del año 1000, en una época en que esta región sufrió la amenaza del Imperio tangut. En 1900, un monje descubrió la entrada sellada de la cueva, en cuyo interior se habían conservado perfectamente los pergaminos de papel y seda gracias al aire seco del desierto. La Biblioteca Británica (British Library) conserva la copia y su versión digital se puede consultar a través de Internet.