Building Bridges: new perspectives on out of Africa

Darren A. Fa,  The Gibraltar Museum, 18-20 Bomb House Lane, Gibraltar darrenfa@gibnet.gidarrenfa@gibnet.gi

Julio Aguilera García, GIEX Grupo de Investigaciones Espeleológicas de Jerez, Cádiz, Spain jaguilera@jet.es 

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Humans originated in Africa, with finds from Atapuerca dated at around 800ka being the first evidence of hominids in Europe. It is generally assumed that they, and all other African dispersals including moderns, were via the Middle East. The Strait of Gibraltar has been in existence throughout the accepted duration of hominid evolution and by extension, an assumed barrier to the passage of hominid species between Africa and Europe. In this work we critically examine this assumption.

There are two main objections to theories that suggest possible trans-Strait movements:

• The width of the Strait (currently at around 14km at its narrowest point) would make crossings extremely difficult;
• Due to evaporative losses, the Mediterranean Sea is continually losing more water than flows into it from rivers, etc. This means that a steady influx of nearly a million cubic metres per second of Atlantic surface water is continually moving into the Alborán Basin (Cano, 1977, 1978a,b; Parilla,1984, Estrada et al., 1985), that is mostly confined to the upper 200m of the water column (Hopkins, 1985).  Such a strong surface current would create problems with attempted crossings.

This combination of distance between land masses and strong currents have been proposed for the existence of an important barrier to hominid migration across the Strait.

The width of the Strait:

During glacial periods, water was locked up as ice with consequent drops in sea levels. One of the main findings is how the move in global climate to a succession of glacials and interglacials, as illustrated by the Greenland Ice Core record (GRIP, 1993), imposed a series of fluctuations in the level of the sea, with drops down to 130m below present levels (Chappell & Shackleton, 1986; Zazo, 1999; Rodríguez Vidal & Gracia, 2000; Zazo et al., 2000).These drops in sea levels during glacial periods effected a narrowing of the Strait, and consequently reduced the barrier effect of a large body of water.

Current flows:

It is assumed that during other interglacials such as the current one, global climatic conditions would have afforded a warm Mediterranean with a deficient water balance and consequently, just as today, Atlantic water would have redressed this balance (favoured by westerlies), creating a surface flow into the Mediterranean. It would seem reasonable to expect that a narrowing of the Strait would increase the strength of these flows.

However, increased river flows together with lower evaporation rates during glacial periods would have produced conditions where the Mediterranean had a positive water balance, and consequently its surface waters would have flowed out into the neighbouring Atlantic region with an accompanying inflow of deep Atlantic water (Mars, 1963; Ruggieri, 1967; Valentine, 1967; Maldonado & Uriz, 1995).

There would then have been extended periods of time on either sides of glacial maxima where current flows would have been negligible, being affected solely by wind and tidal effects (the tidal range in the Strait of Gibraltar is relatively small, averaging around 0.7m).

Based on current estimates of eustatic changes we have used bathymetric data to model what the Strait might have looked like during these slack water pre-and post-glacial periods. Taking an intermediate drop in sea level of 100m (Figure 1b), the Strait are seen to reduce in width considerably and moreover, a number of islands appear that could easily have been used as stepping stones by any species traversing the Strait. Current topographical data are considered suitable as in the Straits area these are primarily bedrock that if anything would have suffered from progressive erosion making the then width of the Strait even less.

With evidence for human crossings over even greater distances (e.g. SE Asia-Australia) it becomes evident that the two-oft cited reasons for refuting theories based on possible hominid migrations across the Strait of Gibraltar are not sufficient to explain why crossings should not have taken place during these pre- and post-glacial periods.

We would predict crossings during pre-and post-glacial periods (that would also be when sea levels would still be low but current rates negligible). So simply by looking at the climate curve for the last 2ma we can start predicting when crossings would have occurred.

But predicting when conditions for a crossing were ideal is not sufficient. Crossings would only have occurred when there existed a pressure to do so. Climate change would have been an important factor in generating these pressures. We present a climate-driven model which illustrates how as climate approaches a glacial phase, increasing aridification of North Africa forces people north during warm/wet periods as the Sahara becomes savannahs and the tropical savannahs become jungle. Then, once this has happened, aridification severs tropical African populations from North African ones.

These North African populations have two possible routes via which they can move northwards – the Middle East and the Strait of Gibraltar. At this stage demographic pressures might become more important as available area is reduced. Later range expansions out of Africa would have met up with northern populations (e.g. Neanderthals) moving south due to escalating cold in Europe. Regardless of whether there was contact via the Strait as was the case in the Middle East, we predict a narrowing of geographical area both for European and North African populations. This leads on to increased pressures for a crossing as climate moves from an interglacial to a glacial, rather than the reverse. We examine the evidence of possible faunal (including human) crossings of the Strait in the Pleistocene.

As far back as the lat interglacial we know that Neanderthals (Gibraltar) and Moderns (South Africa) were exploiting marine resources, so we can assume there is no de facto aversion to the sea. The direction of any crossings, if they occurred, remains enigmatic, and the matter must remain open. Perhaps Africans came into Europe, perhaps Europeans came into Africa. We predict that, all else being equal, the Africans would have been more successful earlier on in history because then there would have been no Europeans. They would also have been most successful right at the end (Solutrean) because then also there were no Europeans, as the Neanderthals had gone and the Moderns from the north had not penetrated. This scenario is compatible with a model of niche expansion instead of replacement. If this is the case, then lack of evidence for a crossing could have more to do with demographic pressures (e.g. competition) than with physical or technological limitations, and poses some new and interesting questions to explore in the future.

References:

Cano, N. (1977). Resultados de la campaña ‘Alborán 73’. Boletin del Instituto Español de Oceanografia, 230: 103-175.

Cano, N. (1978a). Hidrología del Mar Alborán en Primavera-verano. Boletin del Instituto Español de Oceanografia, 248: 52-66.

Cano, N. (1978b). Resultados de le campaña ‘Alborán 76’. Boletin del Instituto Español de Oceanografia, 247: 3-50.

Chappell,J. & Shackleton, N.J. (1986). Oxygen isotopes and sea levels. Nature, 324: 137-139.

GRIP (Greenland Ice-Core Project) Members. (1993). Climate instability during the last interglacial period recorded in the GRIP ice core. Nature, 364: 203-207

Hopkins, T.S. (1985). Physics of the Sea. In Key Environments: Western Mediterranean. [Ed. R. Margalef], Pergamon Press Ltd., Oxford, U.K.

Estrada, M., Vives, F. & Alcaraz, M. (1985). Life and the productivity of the open sea. In Key Environments: Western Mediterranean. [Ed. R. Margalef], Pergamon Press Ltd., Oxford, U.K.

Parilla, G. (1984). Situacíon del giro anticiclónico en el Mar de Alborán en abril de 1980. Boletin del Instituto Español de Oceanografia, 1: 106-113.

Mars, P. (1963). Les faunes et la stratigraphie du Quaternaire méditerranéen. Rec. Trav. St. Mar. Endoume, 28: 61- 97.

Martínez Navarro, B. & Palmqvist, P. (2000). Venta Micena (Orce, Granada): Presence of African mammalian fauna in the South-East of the Iberian Peninsula during the lower Pleistocene. In C. Finlayson, G. Finlayson & D. Fa [Eds.] Gibraltar During The Quaternary. The southernmost part of Europe in the last two million years. Gibraltar Government Heritage Publications Monographs 1, Gibraltar, pp 233-236.

Maldonado, M. & Uriz, M. J. (1995). Biotic affinities in a transitional zone between the Atlantic and the Mediterranean: a biogeographical approach based on sponges. Journal of Biogeography, 22: 89-110.

Rodríguez Vidal, J. & Gracia, J. (2000). Landform analysis and Quaternary processes of the Rock of Gibraltar. In C. Finlayson, G. Finlayson & D. Fa [Eds.] Gibraltar During The Quaternary. The southernmost part of Europe in the last two million years. Gibraltar Government Heritage Publications Monographs 1, Gibraltar, pp.31-38.

Ruggieri, G. (1967). The Miocene and later evolution of the Mediterranean sea. In Aspects of Tethyan Biogeography. [Eds. C. G. Adams & D. V. Ager], Systematics Association Publications, Oxford, U.K. pp. 283-290.

Valentine, J. W. (1967). The influence of climatic fluctuations on species diversity within the Tethyan provincial system. In Aspects of Tethyan Biogeography, [Eds. C. G. Adams & D. V. Ager], Systematics Association Publication Nº 7, London, U.K.

Zazo, C. (1999). Interglacial sea levels. Quaternary International, 55: 101-113.

Zazo, C., Goy, J.L., Hillaire-Marcel, J., Lario, J. Dabrio, C.J., Hoyos, M., Bardaji, T., Silva, P.G. & Somoza, L. (2000). The record of highstand sea-level during the last interglacials. In C. Finlayson, G. Finlayson & D. Fa [Eds.] Gibraltar During The Quaternary. The southernmost part of Europe in the last two million years. Gibraltar Government Heritage Publications Monographs 1, Gibraltar, pp 87-92.

Neanderthals in Vanguard Cave

Isabel Cáceres Cuello de Oro, Area de Prehistoria de la Universitat Rovira i Virgili, Pl. Imperial Tarraco, 1, Tarragona 43005 , España

Yolanda Fernández-Jalvo, Museo Nacional de Ciencias Naturales (CSIC), Jose Gutierrez Abascal, 2. 28006-Madrid, España

Peter Andrews. Department of Palaeontology, The Natural History Museum Cromwell Road, London SW7 5BD, United Kingdom

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Vanguard Cave is one of the archaeological sites located at Governor’s Beach on the eastern side of Gibraltar.  This cave contains a stratigraphical series, over 17 metres thick of coarse sand layers interstratified with brown silt and silty-clay lenses (Goldberg & Macphail , 2000). This site mainly contains middle Palaeolithic deposits with only some late Palaeolithic units on top of the series. This paper explains the taphonomic and zooarchaeological studies of the fossil association recovered from the Middle Area of the section (contexts 154-157) in a small excavation area of 14 m², dated as 93,300 +/-7030 (OxL-1030) (Pettitt & Bailey, 2000).

The taphonomic analysis and spatial distribution of  this fossil association allow us to distinguish three temporary events that extend horizontally according to the ground surface irregularities. These three events appear to follow similar human behavioural  pattern. A rich species composition of both terrestrial (ungulates and carnivores) and marine mammals (seals and dolphins), together with avian fauna, tortoise, molluscs and fish has been recovered. Most remains appear broken following characteristic patterns that suggest human influence. The lithic tools associated to these fossils are mainly made on quartzite and chert, mainly conforming discoidal flakes and retouched artefacts (Barton, 2000). This is characteristic middle Palaeolithic industry.

The skeletal composition suggests that hominids could have a primary access to medium and small sized animals, being transported to the site mostly complete. In contrast to this, the anatomical elements of large sized animals recovered from the site suggest that they were subject of a previous selective transport and individuals did not arrive complete to the site. Breakage patterns and cut-marks suggest that, once in the cave, all animals were intensively butchered, in order to obtain skin, viscera, meat, tendons, and marrow.

Apart from hominid activity, other biostratinomic agents show a low rate of occurrence suggesting a relatively rapid burial of the fossil association. Post-burial taphonomic agents have also a relatively low incidence indicating that traits of these human occupational events have been mostly preserved in situ.

With regard to human occupation, fire played an important role. Apart from the use of fire for cooking or as light and heat sources, we have discovered evidences that Neanderthals used fire to heat bones before breaking them. Experimental work has shown that breakage process becomes easier when bones are previously heated, and most advantageous since the marrow can be easily removed as it solidifies after heating.

The fossil distribution shows a higher abundance of bone fragments next to the cave wall, particularly bigger size fossil fragments, suggesting that this is a toss area as Binford (1981) has characterized. This distribution indicates a development of spatial preparation and cleaning of the settled area. In contrast to the general pattern observed  at Abric Romani, a Catalan middle Palaeolithic site containing a wide series of middle Palaeolithic human occupation units, the fossil distribution at Vanguard Cave does not use hearths as toss areas, since bone fragments and burned fossils are almost absent at these areas. This evidence might mistakenly suggest that the human occupations at Vanguard Cave could be shorter or less intensive than those identified at Abric Romani. Comparison between these two sites, however, shows strong similarities between the Middle Area of Vanguard   and particular areas of activity documented at Abric Romani, areas that are rather committed with animal processing, suggesting a complex spatial organization. The development of long and stable occupational levels such as those observed at Abric Romani (unit Ja) suggests a level of advanced social organization of these human communities that inhabited Gibraltar during middle Palaeolithic.

Pre-Neanderthal and Neanderthal Complexity  

Eudald Carbonell, Àrea de Prehistòria, Universitat Rovira i Virgili,  Pça. Imperial Tarraco, 1 43005 Tarragona, España 

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The twentieth century finished with a heated debate about the last Neanderthals and the emergence of Homo sapiens. Scientists have dealt with several concepts, among which social complexity, acculturation, and extinction have dominated. In its turn, climatic, genetic and cultural hypotheses have played a major role in explaining those phenomena.

Here, our aim is to refocus the debate and to explain that the concept of complexity as a human factor is a product of some acquisitions carried out by the Middle Pleistocene hominids. Under this view, it may be observed that major acquisitions of modern humans were already latent in species such as Homo erectus, Homo heidelbergensis and Homo neanderthalensis.

Hominid species living during the late Middle Pleistocene already knew and controlled fire, blade techniques, art, clothes, language, and even they practiced funerary rituals. Therefore, it is not right to consider that the  emergence of Homo sapiens entailed a cultural break. On the contrary, it must be seen as a process of intraspecific fusion between the biological and the cultural evolution of the hominids that preceded us.

In this sense, Homo neanderthalensis had use of technical means and a social organization enough to consider them modern hominids. Undoubtedly, a cultural issue will not explain their extinction.

The facts of the matter: evidence for symbolic expression in the Châtelperronian and Early Aurignacian.

Randall White, Department of Anthropology, New York University, United States of America

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Early Aurignacian sites have yielded thousands of symbolic objects and representational images. These include personal ornaments, three dimensional sculptures, engravings and paintings. A detailed overview of this evidence for Aurignacian symbolism is presented, with special emphasis on the author's own analysis of Aurignacan personal ornaments from across Europe. Although much of the Aurignacian symbolic record was recovered in pre-modern excavations, there are now many well excavated, well dated and well studied collections from sites such as Castanet, Brassempouy, Fumane, Geissenklosterle, Isturitz and of course Chauvet.

This rich symbolic record for the Aurignacian is in stark contrast to that for the Châtelperronian. Only one site, the grotte du Renne at Arcy-sur-Cure, has yielded significant numbers of symbolic objects attributed to the Châtelperronian. In his excavations at Arcy from the late 1940's through the early 1960's, André Leroi-Gourhan recovered from the grotte du Renne a large sample of personal ornaments, including formed ivory and belemnite beads, pierced animal teeth and ivory rings and pendants. Until recently, these have never been the subject of detailed scientific examination and publication. They have nonetheless been used as ammunition for debates surrounding Neandertal symbolic capacities and relationships between Cro-Magnon and Neandertal populations in the vicinity of 35,000 years ago.

The author's detailed microscopic and technological analysis of the Arcy ornaments, examines them against the backdrop of contemporaneous and more ancient collections of ornaments from early Aurignacian sites across Europe. Such a comparative, stratigraphic-based analysis allows a measure of insight into the oft-raised possibility of Aurignacian/Châtelperronian stratigraphic mixture. Moreover, recent suggestions that Châtelperronian techniques of ornament manufacture (notably drilling techniques) were distinctly different from those of the early Aurignacian are shown to be false when well provenienced, well dated Aurignacian and Châtelperronian ornaments are studied. Nonetheless, certain quantitative tendencies (e.g., species choice for animal teeth, preference for suspension by means of basal incisions around the circumference of the tooth root) of the Arcy Châtelperronian ornaments stand in some contrast to early Aurignacian ornamental assemblages.

Technological analyses of symbolic representations can only point to convergences and divergences among collections currently attributed to different culture stratigraphic units of the early Upper Paleolithic. While there is currently great interest in jumping to larger questions concerning acculturation between Neandertals and Cro-Magnons, and Neandertal capacities for symbolic behavior, the currently available Châtelperronian record cannot be used to respond with certainty to such questions.