One of the most important controversies about human evolution and expansion is when and by what route the first hominids arrived in Europe from the African continent. Now, geological dating techniques at the Orce sites (Baza basin, Granada, Spain) place the human remains found in this area as the oldest in Europe, at approximately 1.3 million years old. These results reinforce the hypothesis that humans arrived in Europe through the south of the Iberian Peninsula, through the Strait of Gibraltar, instead of returning to the Mediterranean via the Asian route. The study, led by Lluís Gibert, researcher and lecturer at the University of Barcelona’s Faculty of Earth Sciences, has involved the participation of researchers from the Berkeley Geochronology Centre and Murray State University (United States).
Analysis of a new sampling area
The new dating has been based on the analysis of the paleomagnetism of an area of the Orce region, which has never been sampled before and which has been protected from the erosion that this basin has suffered over the years. This technique is a relative dating method based on the study of the inversion of the magnetic poles of the planet due to the internal dynamics of the Earth. These changes do not have a specific periodicity, but they are recorded in the minerals and make it possible to establish time periods from the different magnetic events.
These new data are very precise thanks to the long sedimentary sequence that outcrops in Orce. “The uniqueness of these sites is that they are stratified and within a very long sedimentary sequence, more than eighty metres long. Normally, the sites are found in caves or within very short stratigraphic sequences, which do not allow you to develop long palaeomagnetic sequences in which you can find different magnetic reversals”, says Lluís Gibert.
The researchers have been able to identify a magnetic polarity sequence “with five magnetic events that allow them to place the three Orce sites with human presence between the Olduvai and Jaramillo subchron, that is, between 1.77 and 1.07 million years ago (Ma)”, says the researcher. Subsequently, they have applied a statistical age model to accurately refine the chronology of the different stratigraphic levels with a margin of error of only 70,000 years. The result of this innovative methodology is that the oldest site with human presence in Europe would be Venta Micena with an age of 1.32 Ma, followed by Barranco León, with an age of 1.28 and finally Fuente Nueva 3, with an age of 1.23 Ma. “With these data, the other major site on the peninsula, the Sima del Elefante in Atapuerca, would be relegated to second place, far behind Orce, between 0.2 and 0.4 Ma more modern”, adds the researcher.
Fauna underpins the antiquity of the site
To complete the dating, the study has also analyzed the fauna found at the different sites in Orce, as this is different depending on the period, and compared it with that found at other Early Pleistocene sites in other parts of Europe.
In this sense, the paper presents a detailed analysis of the micromammals and large mammals from all the Orce sites, carried out by the expert Robert Martin, based on the palaeontological collections stored at the Museum of the Catalan Institute of Palaeontology Miguel Crusafont (IPS) in Sabadell. “The results indicate that the small and large fauna of Orce is more primitive than, for example, that of the Sima del Elefante, where the evidence shows that the rodent Allophaiomys lavocati is more evolved than the Allophaiomys recovered from the Orce sites”, Gibert explains.
Another relevant indicator of the age of the Orce sites is the absence of the ancestors of the pigs. “These animals are considered to be Asian immigrants and have not been found in any European site between 1 and 1.5 Ma, while they have been found in the Sima del Elefante, supporting that the Orce fauna is older”, explains the researcher.
Evidence pointing to passage through Gibraltar
This new dating would be added, according to the researcher, to other evidence that would tip the balance in favour of the colonization of Europe through the Strait of Gibraltar, rather than the alternative route: the return to the Mediterranean via Asia, such as “the existence of a lithic industry with similarities to that found in the north of the African continent and also the presence of remains of African fauna in the south of the peninsula, such as those of Hippopotamus, found in the sites of Orce, and those of Theropithecus oswaldi, an African primate similar to a baboon, found in the Victoria cave, a site near Cartagena (Murcia), non-existent anywhere else in Europe”.
“We also defend the hypothesis — adds the researcher — that they arrived from Gibraltar because no older evidence has been found at any other site along the alternative route”.
These new data are very precise thanks to the long sedimentary sequence that outcrops in Orce.
Similarity with hominids from the island of Flores
With these results, the researchers point to a “diachronism” between the oldest occupation of Asia, measuring 1.8 Ma, and the oldest occupation of Europe, which would be 1.3 Ma ago, so that African hominids would have arrived in southwestern Europe more than 0.5 Ma after leaving Africa for the first time about 2 Ma ago. “These differences in human expansion can be explained by the fact that Europe is isolated from Asia and Africa by biogeographical barriers that are difficult to overcome, both to the east (Bosphorus Strait, Dardanelles, Sea of Marmara) and to the west (Strait of Gibraltar). Humanity arrived in Europe when it had the necessary technology to cross maritime barriers, as happened before a million years ago on the island of Flores (Indonesia)”, says Gibert. In this sense, the researcher adds that the Gibraltar route currently requires crossing up to fourteen kilometres of sea route, but “perhaps in the past this distance was shorter at certain times due to the high tectonic activity in this region and the fluctuations in sea level that favoured migrations”.
“As cited in the paper — he adds —, we have identified other migrations of African fauna through Gibraltar at earlier times, 6.2 and 5.5 Ma ago when the Strait of Gibraltar was very narrow”.
Human remains in Orce
A total of five human remains were found at the Orce sites since excavations began in 1982 by the palaeoanthropologist Josep Gibert. Firstly, two fragments of humerus bitten by hyenas were found at Venta Micena, as well as parts of a cranial fragment consisting of two parietals and an occipital, associated with an abundant Early Pleistocene fauna. The human provenance of these remains generated great controversy for years, although independent palaeoproteomic studies by the universities of Granada and San Francisco identified human proteins in the remains.
The subsequent discovery at the nearby sites of Barranco León and Fuente Nueva 3 of two human molar teeth and thousands of Olduvayan lithic tools — one of the first human lithic industries — as well as cut marks on bones “served to consolidate the evidence of the presence of hominids in the Early Pleistocene at Orce”, concludes Lluís Gibert.