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Quaternary International 223-224 (2010) 36e44

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Early hominid dispersals: A technological hypothesis for “out of Africa”

Eudald Carbonell a, Robert Sala Ramos a,*, Xosé Pedro Rodríguez a, Marina Mosquera a, Andreu Ollé a,Josep María Vergès a, Bienvenido Martínez-Navarro a,b, José María Bermúdez de Castro c

a Institut Català de Paleoecologia Humana i Evolució Social (IPHES). Àrea de Prehistòria, Universitat Rovira i Virgili. Avgda. Catalunya, 35. 43002 Tarragona, Spainb ICREA. Institució Catalana de Recerca i Estudis Avançats, SpaincCentro Nacional de Investigación sobre Evolución Humana (CENIEH), Burgos, Spain

a r t i c l e i n f o

Article history:Available online 25 February 2010

* Corresponding author. Tel.: þ34 9779730; fax: þ3E-mail address: robert.sala@urv.cat (R. Sala Ramos

1040-6182/$ e see front matter � 2010 Elsevier Ltd adoi:10.1016/j.quaint.2010.02.015

a b s t r a c t

Homo is the only genus that responds to environmental pressures by adopting such strategies as non-standardized behaviour, a general diet, and technology. Considering that basic idea, this paper intro-duces the general hypothesis that the Pliocene and Early Pleistocene Homo dispersals within and out ofAfrica were consequences of that human characteristic behaviour. In particular, they were driven bya process starting with the emergence of technology, followed in a second phase by its socialization.From this point, social reorganization within communities (changing behaviours and social, cultural andeconomic strategies) occurred, driving demographic growth, and frequently geographic expansion.

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1. Introduction

The end of the twentieth century witnessed increasing interestin and debate about the circumstances that led Plio-Pleistocene andEarly Pleistocene hominids to disperse out of Africa (Dean andDelson, 1995; Carbonell et al., 1996, 1999a, 2008a; Arribasand Palmqvist, 1999; Turner, 1999; Aguirre and Carbonell, 2001;Bar-Yosef and Belfer-Cohen, 2001; Mithen and Reed, 2002). Thedebate has focused on resolving when, how and where the earliestwaves of hominid dispersal occurred, with special emphasis on theparticular mechanisms that conditioned and determined thesedispersals and the ways in which early Homo arrived and settledEurasia (Rolland, 1992; Carbonell et al., 1996, 2008a; Dennell andRoebroeks, 1996; Martínez-Navarro et al., 1997; Oms et al., 2000;Roebroeks, 2001).

As the debate continues, it shows how little is known aboutcertain key aspects of human evolution. In particular, some of thehypotheses proposed during the last decade have to be amendeddue to the change in the knowledge about the chronology of thedispersals. Elsewhere, it was proposed that the technological shiftto Mode 2 in Africa could have pushed some Mode 1 populationwithin Africa to move into Eurasia (Carbonell et al., 1999a). Thishypothesis was based both in a younger chronology for the Dmanisirecord and in the consideration that Homo antecessorwas certainlyan African species. Today, the date for Dmanisi exceeds that of thefirst evidence for Mode 2 in Africa (Asfaw et al., 1992; de Lumley

4 977558386.).

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et al., 2002), and H. antecessor may have an Eurasian origin(Carbonell et al., 2005). Therefore, the extent to which technologyinfluenced hominin dispersals is the purpose of this paper.

Some issues can be taken into consideration as starting points: 1.There was not a single out-of-Africa hominin dispersal event; 2.Based on current knowledge, the only hominin genus that left Africaduring the Plio-Pleistocene was Homo; 3. Other hominin generacoexisting with Homo evolved and went extinct in Africa, particu-larly Australopithecus and Paranthropus. The latter may have startedto adopt a generalist feeding strategy, combining scavenging,hunting and gathering (Sillen, 1992; Lee-Thorp et al., 1994, 2000).Even though theymay have also invented technology,Homowas theonly hominin genus that was successful in dispersing out of Africadue to its systematic application of a set of adaptive strategies(Carbonell et al., 2008a): systematic adoption of technology asa mean for resources supply, a generalist diet (as has been proposedby Anton et al., 2002, and Anton and Swisher, 2004) and a non-standardized behaviour. Technology meant that humans were ableto diversify their behaviour, and so they disposed of a wide range ofresponses to better adapt to new and heterogeneous situations. Insum, technology appears as the more powerful adaptation forhumans.

Despite this role, hypotheses based on technological develop-ment to explain human dispersals and evolution have not beenthoroughly developed. The significance of the different stageswithin each Mode on dispersals should be considered, not only theshift to Mode 2. It is also appropriate to review the chronology ofdifferent dispersal events and to show the possible relation totechnological phases. This approach, termed the “The Out of Africa

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Technological Hypothesis”, emphasises the role played by tech-nology in human expansions (Carbonell et al., 1999a, 2008a).

2. Current data for the earliest Homo dispersals out of Africa,and into Western Eurasia

According to current empirical data, the earliest known tools aremodified stones recovered from archaeological sites in Central EastAfrica, and date at a maximum of 2.6 Ma (Kibunjia, 1994; Semawet al., 1997, 2003; Delagnes and Roche, 2005). These lithic recordsare abundant and diversified, suggesting that technology was notnewborn, but already generalized by this time (Panger et al., 2002).Technology may have emerged previously, and this period mayrepresent the time of its first complete socialization (Carbonellet al., 2009). It is within this hypothetical framework of general-ized tool production and use that early Homo dispersals withinAfrica and beyond can be understood (Carbonell et al., 2007).

The oldest Homo fossils known out of Africa come from the siteof Dmanisi (Georgia) dated to 1.81 Ma (Gabunia and Vekua, 1995;Gabunia et al., 2001; de Lumley et al., 2002). They have beenclassified as Homo georgicus (Gabunia et al., 2002), and theirprimitive features and variability suggest that these hominins areextremely close to the Homo speciation threshold. The Dmanisiarchaeological record in addition to human fossils is composed bya large lithic assemblage displaying Mode 1 features close to thatshown by the African sites more than 2.0 Ma (de Lumley et al.,2005; Mgeladze, 2008).

The current known Western Eurasian Early Pleistocene sites aresignificantly younger than Dmanisi, and they offer different quali-ties of chronological and archaeological (Fig. 1) and palae-ontological data. Pirro Nord (Italy) is claimed to be around 1.4 Maon biochronological markers (Arzarello et al., 2009). Also in Italy,Monte Poggiolo has an age of 0.9 Ma based on both by paleomag-netism and ESR (Peretto et al., 1998; Falguères, 2003). The lastItalian site to be mentioned is Ceprano, where a human calvariumhas been previously ascribed by stratigraphical correlation to a timespan between 0.8 and 0.9 Ma (Ascenzi et al., 1996; Manzi et al.,2001). However, a Middle Pleistocene age has been proposed forthis site (Muttoni et al., 2009).

In France there are two main Early Pleistocene sites: Pont-de-Lavaud and Vallonnet. The latter has been dated by means ofbiostratigraphy, paleomagnetism and ESR to the Jaramillo magneticsubchron, between 0.99 and 1.07 Ma (de Lumley, 1988; Yokoyamaet al., 1988; de Lumley et al., 2009). To date, Pont-de-Lavaud isthe oldest site in France, with an age between 1.0 and 1.2 Madetermined by ESR (Despriée et al., 2006, 2009). It is also thenorthernmost Early Pleistocene site in Western Europe.

In Southern Spain, the archaeological remains of Fuente Nueva 3and Barranco León 5 sites in the region of Orce have been dated at1.2e1.3Ma on the basis of paleomagnetic and biochronological data(Oms et al., 2000; Toro-Moyano et al., 2009). Finally, in NorthernSpain two of the karstic sites of Atapuerca display Early Pleistocenelevels: levels TD3-4 to TD7 in the Gran Dolina cave and TE7 to TE16in Sima del Elefante cave. The archaeological assemblages fromTD3-4 and TD5 have been interpreted as products of short humanoccupations. In contrast the overlying level TD6 represents anintense occupation, with features of a base camp (Carbonell et al.,1995, 1999b), including human remains of H. antecessor(Bermúdez de Castro, 1997; Carbonell et al., 2005). TD6 has beendated through biostratigraphy, paleomagnetism and ESR giving anage of 0.8e0.9 Ma (Parés and Pérez-González, 1999; Falguères et al.,1999; Berger et al., 2008). Among the Early Pleistocene levels ofSima del Elefante, TE9 stands out because of the association of lithicartefacts (Fig. 2), anthropically broken and cutmarked bones, andhominin fossils preliminary assigned to H. antecessor (Carbonell

et al., 2008b). Its age has been established in 1.2 Ma by means ofpaleomagnetism, biostratigraphy and cosmogenic nuclides. To date,the Atapuerca complex is unique in offering a set of sites and levelswith different ages in the second half of the Early Pleistocene, withboth cultural and biological information on human evolution inWestern Eurasia.

Although Mode 2 technology was already developed in Africa atthe time of the human occupation of Europe, all the Early Pleisto-cene European sites display Mode 1 lithic assemblages. In general,the European Mode 1 technology is characterized by the wide-spread use of knapping methods to produce simple flakes. Thesemethods were sometimes organized and systematic, but theproduction processes were basic, and lacked different stages ofknapping (i.e., preparation of the cores): they lacked processcomplexity. This Mode 1 technology also produces few smallretouched flakes and some heavy-duty pebble tools, both mini-mally shaped (Fig. 3). Although these are the general traits forMode1, the differences between the oldest one in Eurasia, that of Dmanisiand that of Gran Dolina-TD6 from Atapuerca cannot be neglected.Dmanisi is claimed to have similar archaic technological features tothe African sites between 2.6 and 2.0 Ma (de Lumley et al., 2005).Gran Dolina-TD6 shows some small shaped tools, as well as, for thefirst time in Europe, an incipient production of bigger flakes to beknapped as cores but never shaped into tools (Fig. 4) (Carbonellet al., 1999b; Rodríguez, 2004). The dominant exploitation strate-gies are those common in Mode 1, and include mainly theorthogonal technique but also centripetal and unipolar longitudinalknapping.

3. Technological hypothesis for the first out of Africa event

In the authors' view, the dispersals of Homo were triggered byethological and cultural mechanisms that differed significantlyfrom those of other mammal species, particularly as far as theirsocial behaviour was concerned (Rolland, 1992; Tchernov, 1992;Turner, 1992; deMenocal and Bloemendal, 1995; Roebroeks,2001). A crucial factor that determined the earliest dispersals ofHomo was their capacity to socialize operational intelligence: theircapacity to make tools and to diffuse this tool-making behaviourwithin the Homo species. Technology started to play its crucial rolein the social structures of these early Homo communities. Gener-alizing tool production and use generated a phenomenon called“social reorganization”. This concept is used here to describe thesocial, cultural and subsistence behavioural changes derived fromthe adoption of new technical skills by a population.

The following list summarizes the chain of processes proposedto lead to the earliest Homo dispersals out of Africa (Fig. 5). Itcorresponds to the first technological rise and development but italso offers a hypothetical framework to understand the rise andgrowing of any new evolutionary phase:

1. Proposal for the emergence of tool production and consequentrise of operational intelligence at the end of the Pliocene, around3 Ma, even though the current earliest record is dated at 2.6 Ma.

2. Generalization and socialization of tool production amongHomo rudolfensis and Homo habilis communities around2.3e2.4 Ma. Once the use of technology has been generalized ina community, new opportunities emerge and improvements areeasier to adopt. Therefore, socializing tool production may haveled to faster responses to subsistence needs and otherchallenges.

3. Adoption of new behaviours and reorganization of adaptivestrategies (i.e., social reorganization). Socializing tool produc-tion may have forced a reorganization of the social structure ofthe community by creating a cultural background that gave

Fig. 1. Mode 1 lithic industry from Early Pleistocene European sites. 1e2. Cores on quartz pebbles, from Pont de Lavaud (Despriée et al., 2009). 3. Flake on quartz with denticulateretouch, from Pont de Lavaud (Despriée et al., 2009). 4. Prismatic core on flint, with bipolar knapping, from Barranco León (Toro-Moyano et al., 2009). 5. Orthogonal core onlimestone, Fuente Nueva 3 (Toro-Moyano et al., 2009). 6e7. Flint flakes, Fuente Nueva 3 (Toro-Moyano et al., 2009). 8, Chopper on flint, Monte Poggiolo (Peretto et al., 1998); 9, Coreon flint, Monte Poggiolo (Peretto et al., 1998); 10, Limestone chopper Vallonnet (de Lumley et al., 2009).

E. Carbonell et al. / Quaternary International 223-224 (2010) 36e4438

support to new ideas. New ideas and improvements must betested before they are adopted. Complexity increased, so anemerging form of social specialization may have developed,creating an incipient form of new social structure.

4. Demographic growth and evolutionary success of Homo asa consequence of having improved its adaptive capabilities.

5. Occupation of new spaces. The dispersals began as a result ofdemographic growth. Geographic features and barriers (e.g., theRift Valley) played a significant role in the routing of thedispersals.

4. Why did mode 2 never reach Europe before 0.8 Ma?

The proposed technological hypothesis has to enlighten the firsthuman dispersal into Eurasia but it is also compelled to explainwhyMode 2 populations took so long time to reach Europe (Fig. 6). Thefirst Asian Mode 2 record is the well known assemblage of ‘Ubei-diya with a date around 1.4 Ma (Bar-Yosef and Goren-Inbar, 1993).Although the site of Isampur in India has been claimed to be 1.2 Ma(Paddayya et al., 2002), there are some controversies concerningdating (Acharyya, 2003; Paddayya, 2003; Chauhan, 2009). This siteis interesting for the quarrying behaviour demonstrated by itsrecord (Petraglia et al., 1999), but especially because it may exem-plify the continuity of population since ‘Ubeidiya. Conversely,

taking into account the caution regarding its dating, it appears thatthe Mode 2 dispersal event exemplified by ‘Ubeidiya was restrictedto the Near East and did not expand beyond. In addition its tech-nological characteristics, proposed as archaic Acheulean (Bar-Yosefand Goren-Inbar, 1993; Bar-Yosef and Belfer-Cohen, 2001) arecloser to the oldest African Mode 2 entities than to the Eurasianones. Neither in Asia nor in Europe has such an archaic Mode 2 everbeen described.

The attested expansion of Mode 2 through Eurasia seems to benot older than 0.8 Ma, as it appears at sites at both corners of thecontinent. In China, a classical Mode 2 site at Bose with handaxes,cleavers and picks, 0,8 Ma old, has been described (Hou et al.,2000). Slightly younger is the European Mode 2 record: to date,no European Mode 2 site is older than 0.6 Ma, Notarchirico in Italy(Piperno, 1999) and Arago in France (de Lumley and Barsky, 2004;Falguères et al., 2004) being the oldest.

These Eurasian sites show technological features that areclearly different from those present at ‘Ubeidiya. Interestingly,another Near Eastern site has both an age and technologicalcharacteristics that are closer to the Mode 2 systematic expansion:Gesher Benot Ya'aqov, 0.8 Ma (Goren-Inbar, 1992; Goren-Inbaret al., 2000).

Mode 2 has been characterized by the production of large tools,mostly on flakes, that usually show bilateral symmetry, such ashandaxes, cleavers and picks. At this stage, trihedral-tip shapes

Fig. 2. Atapuerca Sima del Elefante-TE9. a and b, Flakes on Cretaceous flint; c, Flake on Neogene flint.

E. Carbonell et al. / Quaternary International 223-224 (2010) 36e44 39

become part of the technique, and they share the above mentionedconcept of symmetry. Despite these general features, sometemporal trends can be detected in its evolution. The presence ofcrude handaxes along with spheroids and choppers in sites as

Fig. 3. Atapuerca Gran Dolina-TD6. a, Orthogonal core o

‘Ubeidiya is in contrast with the well developed technique on largetools, already standardised, clearly present at other localities suchas Gesher Benot Ya'aqov. The former set of traits seems to be absentfrom Eurasian sites.

n Neogene flint; b, Heavy-duty tool on limestone.

Fig. 4. Atapuerca Gran Dolina-TD6. Large flake on Neogene flint used as core.

E. Carbonell et al. / Quaternary International 223-224 (2010) 36e4440

What could be the explanation for the dispersal delay ofa technology considered more efficient than the former Mode 1,and already present in the Near East ca. 1.4 Ma at ‘Ubeidiya? The‘Ubeidiya faunal complex offers Eurasian species, demonstratingthat hominin introduction in new ecological conditions was actu-ally effective. A possible explanation is that a good adaptation ofEurasian Mode 1 populations since Dmanisi time posed a barrier tothe expansion of a new wave of human populations, likely withoutthe technical and social maturity needed to succeed in sucha confrontation.

5. A technological hypothesis for the second large-scaledispersal

Following the same chain of processes exposed for the Mode 1emergence, socialization and expansion, a similar series of stagesare suggested concerning Mode 2:

1. Emergence of Mode 2 technology, maybe around 1.8 Ma oreven slightly earlier. According to current data, the lithic tools ofKokiselei (West Turkana, Kenya) (Roche et al., 2003), KonsoGardula (Ethiopia) (Asfaw et al., 1992), and Rietputs Formation(Vaal River, South Africa) (Gibbon et al., 2009) are the earliesttraces of Mode 2, with an age of 1.7e1.6 Ma. If the same evolu-tionary model proposed for Mode 1 is applied, Mode 2 appears

to be already developed at the referred sites. Therefore, itprobably emerged before this date.

2. Socialization of Mode 2, which expanded across the Africancontinent until reaching the Levantine Corridor, around 1.4 Ma.The socialization of Mode 2 may have been delayed because ofsome degree of territorial competition posed by Mode 1 pop-ulations, who did not adopt the new skills and behaviours, andacted as a barrier for Mode 2 expansion at this early stage.

3. New economic and social reorganization within the Homospecies after the Mode 2 socialization process, leading todemographic growth.

4. Competition within genus Homo in Africa would have forcedthe Mode 1 communities that did not adopt Mode 2 technologyto leave the continent (Carbonell et al., 1999a). Alternatively, theoldest Mode 1 communities of Eurasia, being relatively isolatedfrom the AfricanMode 2 innovations, may have expanded acrossthe continent from 1.8 Ma to around 1 Ma (Carbonell et al.,2008a). Both hypotheses would explain why Mode 1 stillappears in Eurasia at around 1 Ma, when Mode 2 was alreadydeveloped in Africa (Carbonell and Rodríguez, 2006). The firsthypothesis assumes an African origin for the communities thatoccupied Europe ca. 1.4 Ma assisted by Mode 1 industries, whilethe latter assumes that these groups were Eurasian.

5. Demographic growth derived from a systematic introductionand generalization of Mode 2 technology. The high efficiencyand advantages of this technology led again to dispersals out of

Fig. 5. First large-scale Homo dispersal inside and out of Africa. There are depicted the first archaeological complexes in Africa along with the main Early Pleistocene Mode 1 sitesboth in Africa and Eurasia discussed in the text. The main attention has been put on the European archaeological record, related to the more recent Mode 1 large-scale dispersalevent.

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Africa, this time by Mode 2 communities. Within this context,a more evolved species with a brain of around 1000 cm3 wasresponsible for both the second large-scale dispersal event, andthe Mode 2 occupation of Eurasian landscapes. This widedispersal is documented by synchronous evidence from the sitesof Gesher Benot Ya'aqov (Levantine Corridor) (Goren-Inbar et al.,2000; Saragusti and Goren-Inbar, 2001; Sharon, 2007), Bose(China) (Hou et al., 2000) and later at the earliest EuropeanMode 2 sites of Notarchirico (Italy) (Piperno, 1999) and Caune del'Arago (France) (de Lumley and Barsky, 2004).

This Acheulean (Mode 2) sequence resembles the Oldowan one(Mode 1), and it shows the importance of conceptualizinga continuous process of social reorganizationwithin our genus; onethat operates through new acquisitions and their socialization, theconsequent social reorganization of groups, and the final outcomeof demographic growth leading to massive dispersals.

6. Discussion

The existence of a connection between ecological changes andbehavioural and cognitive evolution of hominins has been dis-cussed previously (Vrba et al., 1995; Macho and Leakey, 2009). Theecological framework (deMenocal, 2004) indicates main climateshifts at 2.8, 1.7 and 1.0 Ma. Current data about the chronology ofhuman dispersals into Eurasia do not match the date of theseclimatic shifts. The first human dispersal may occurred shortly after2.3e2.4 Ma, as supported by the evidence coming from archaeo-logical sites such as Dmanisi (Georgia) (Gabunia and Vekua, 1995;de Lumley et al., 2002), Riwat (Pakistan) (Dennell et al., 1998),Longgupo (Wanpo et al., 1995) and Renzidong (China) (Dong,2006), all around 2.0 Ma or slightly younger. Although Longgupo

has been recently revisited and reanalysed (Ciochon, 2009) analysishas been directed towards the recognition of primate fossils ashumans, not to the anthropic origin of the recovered tools. Thesemaintain their actual human nature. All these sites retain the veryarchaic traits from the AfricanMode 1 previous to 2.0 Ma and came,clearly, from a very ancient dispersion flow.

It has been stressed that during the Early Pleistocene, severalspecies of mammals, such as Hippopotamus antiquus, Megantereonwhitei and Theropithecus oswaldi, dispersed out of Africa under theinfluence of climatic and ecological pressures sometimes alongwith humans (Martínez-Navarro, 2004; Rook et al., 2004).However, these dispersals did match the complexity of those ofhumans neither in age nor in space.

Certainly, climate change and its associated shifts in plant andanimal communities represent factors of environmental pressure.The adaptive response of hominins to such changes was to acquireand socialize extrasomatic behaviour, that is to say, they system-atically developed technology. Then, human adaptation is notdirect but mediated. This process triggered behavioural changesamong these hominin groups because their operational intelligenceincreased; that is, they increased their capacity to obtain energyfrom the environment by diversifying the strategies for life andfood acquisition. In turn, this development led to immediatedemographic growth within the genus Homo, which would havebeen much more competitive and have exerted more pressure inthe environment than any other genus.

This may have been the way in which Mode 1 technology(Oldowan technology) contributed to the communities that firstexpanded across the African continent, as has been documentedfrom South African sites such as Sterkfontein and Kromdraai(Kuman, 1994; Kuman et al., 1997) to North African sites, such asAin Hanech (Algeria) (Sahnouni and Heinzelin, 1998; Sahnouni

Fig. 6. Second large-scale Homo dispersal event leading to the Mode 2 expansion into Eurasia. There have been shown the three earliest Mode 2 African records along with the sitesdemonstrating the dispersal of this technology to Eurasia. The sites clearly related to the phase of resocialisation leading to the Mode 2 systematic dispersal into Eurasia have beenhighlighted.

E. Carbonell et al. / Quaternary International 223-224 (2010) 36e4442

et al., 2002), and at the same time across the Eurasian continent.This shows a complex net of human dispersals favoured by thenewborn technical and social skills.

The evidence from Dmanisi (Georgia) (Gabunia and Vekua,1995; Gabunia et al., 2002) together with the Homo erectusremains from Java (Indonesia) (Swisher et al., 1994) and Yuanmou(China) (Zhu et al., 2008) are the oldest examples of the firstdispersal waves, which are products of the reorganization of socialbehaviour among our earliest Homo ancestors. In this respect, thespecimen D3444/D3900 from Dmanisi (Georgia) suggests thatsome degree of social complexity may have existed within the earlyHomo communities: this specimen is the mandible of a toothlessindividual displaying strong alveolar absorption. This individuallikely needed some care by other individuals to survive, pointing toaltruistic social cooperation (Lordkipanidze et al., 2005). Thisbehaviour coincideswith the earliest large-scaleHomo dispersals. Itmay be part of the social reorganization processes derived from thesocialization of technology. Evidence for the care of old individualsis an indicator of a sense of social coherence that may have enableddispersals to occur.

Possibly, several and continuous dispersals out of Africa haveoccurred, not necessarily large-scale waves of migration. However,the stronger flows were related to the emergence and socializationof new behavioural acquisitions by Homo populations. Therefore, itis proposed that large-scale dispersal events took place twice:firstly, after the social reorganization of Mode 1 (Oldowan tech-nology), and secondly after the social reorganization of Mode 2technology (Acheulean technology). In this hypothesis, the formertook place slightly after the first technology occurrence in EastAfrica, before 2.0 Ma and produced the human expansion throughand outside Africa leaving the archaeological records in South andNorth Africa and Asia. For the latter, two main flows are proposed.

A first expansion of Mode 2 around 1.5 Ma leave the record of‘Ubeidiya (Bar-Yosef and Goren-Inbar, 1993) and its pressure overthe Mode 1 populations in the Near East could be the origin for thelater expansion of Mode 1 and H. antecessor to Western Europe(Carbonell et al., 2008b). The first Mode 2 expansion into Near Eastseems to have been not strong enough to reach other Eurasianregions.

Finally, the late expansion of Mode 2 throughout Eurasia,beyond the Near East, has to correspond to a moment of importantsocial reorganization and demographic growth inside Mode 2populations both in Near East and Africa. This relationship isproposed because its age, around 0.8e1.0 Ma, and because of thecharacteristics of current early Acheulean in Eurasia: Bose (Houet al., 2000), Notarchirico (Piperno, 1999) and Arago (de Lumleyand Barsky, 2004). All these sites present a technological recordthat corresponds to a very advanced phase of Mode 2 evolution,different from the primitive one of ‘Ubeidiya (Bar-Yosef and Goren-Inbar, 1993) but close to that of Gesher Benot Ya'aqov (Goren-Inbaret al., 2000), whose age also has been established at 0.8 Ma. Thetechnology of this site has been related to other African sites of thesame age (Goren-Inbar, 1992; Saragusti and Goren-Inbar, 2001),a hypothesis that is coherent with a new phase of socialization anddemographic growth all over Africa and Near East.

7. Conclusion

The dispersals of Homo may be understood as the result of ouruniqueness within the hominin family. The capacity of toolproduction lies at the centre of this uniqueness, strongly influ-encing our social behaviour.

The factors that trigger these dispersals must be sought in thedifferent kinds of pressures that the environment imposes on

E. Carbonell et al. / Quaternary International 223-224 (2010) 36e44 43

populations living in different ecosystems. However, hominins, associal primates, have a high capacity of social reorganization,especially when developing and generalizing the use of tools toobtain energy and means for self-defence. The process can besummarized as follows: 1) technological developments, 2) sociali-zation (i.e., the generalization of these developments within thegroup), 3) social reorganization (i.e., a dynamic process thatinvolves changes in behaviour, social skills and subsistence strate-gies), 4) demographic growth as a result of the success of socialreorganization, and eventually, 5) geographic expansion.

The key issue in the hominin dispersals from the Africancontinent is that Homo acquires information from the environmentdifferently than other mammals, and has the ethological skill tosocialize this information. Another feedback mechanism makessocial reorganization possible, which improves our neurologicaland operative capabilities. This can be seen in the increase in brainsize and the development of manual skills. Both are necessaryconditions for the development of cognitive, social and culturalcomplexity, which in turn enables the development of subsistencestrategies for extracting energy from the environment with moreefficiency and less effort. The result is demographic growth andbehavioural flexibility, allowing Homo to adapt to ecosystems thatare difficult or impossible to access under natural conditions. Thiswas not possible for other hominin genera: hence our uniqueness.Another evidence for this uniqueness is the D3444/D3900 spec-imen from Dmanisi and the social cohesion that it demonstrates.

Up to the present, our species has continued to apply the samemain adaptive strategy, leading us to the socialization of newdiscoveries at unthinkable levels when compared to earlier evolu-tionary stages of our genus: the 6.8 billion Homo individuals livingon our planet corroborate this point and show to what extentsocialization among our species has accelerated.

Acknowledgements

We thank John Bates from the Servei Linguistic-URV forcorrections of the manuscript and Carolina Mallol for reviewing theformer English version. We also thank J. Mestre and N. Sanchis forthe picture and drawings. Some of the authors of this paper belongto the Atapuerca Research Project, supported by Ministerio deEducación y Ciencia Coordinated Projects BOS2003- 08938-C03-01,�02, and �03, the Consejería de Cultura y Turismo of the Junta deCastilla y León, and the Fundación Atapuerca. Part of this work hasbeen also supported by the Ministerio de Educación y CienciaProject CGL2006-13808-C02-01/BTE.

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