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Quaternary International 295 (2013) 69e72

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The Quaternary megafaunal extinction and the fate of Neanderthals:An integrative working hypothesis

Policarp Hortolà b,c, Bienvenido Martínez-Navarro a,b,c,*

a Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Catalonia, SpainbÀrea de Prehistòria, Universitat Rovira i Virgili (URV), Tarragona, Catalonia, Spainc Institut Català de Paleoecologia Humana i Evolució Social (IPHES), Plaça de la Imperial Tàrraco 1, ES-43005 Tarragona, Catalonia, Spain

a r t i c l e i n f o

Article history:Available online 22 February 2012

* Corresponding author. Institut Català de PaleoeSocial (IPHES), Plaça de la Imperial Tàrraco 1, ES-4300

E-mail address: bienvenido@icrea.es (B. Martínez-

1040-6182/$ e see front matter � 2012 Elsevier Ltd adoi:10.1016/j.quaint.2012.02.037

a b s t r a c t

The last great extinction that has happened throughout the Earth’s life history (the Quaternary Mega-faunal Extinction) exterminated more than 178 species of the world’s largest mammals. Differenthypotheses to explain this extinction have been proposed, from environmental catastrophes to predatoravoidance, or even volcanic activity and meteorite impact. Currently, many researchers see the SixthExtinction as a total or partial result of past climatic changes. The mechanism of Neanderthal extinctionis a controversial issue of broad interest among human palaeontologists and evolutionary biologists. Thispaper presents an integrative working hypothesis to elucidate this extinction, based on their killing/predation as habitual part of the competition strategy of anatomically modern humans, and in thecontext of the wider Quaternary Megafaunal Extinction. Following this working hypothesis, Neanderthalextinction should be seen as being a mere branch of the Quaternary Megafaunal Extinction. Theecologically K early Homo sapienswould exterminate other K species, most of them megafauna, includingthe medium-sized non-sapiens human species. Neanderthals were part of the large mammal preypotentially hunted by our species, in the same way that historically orang-utans, gorillas and chim-panzees still are. Most probably, the same happened whenever a technologically more evolved Homospecies overlapped with other less technologically evolved one.

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1. Introduction

Six great extinctions have happened throughout the Earth’s lifehistory (Alvarez et al., 2009). The last one (the Quaternary Mega-faunal Extinction) exterminated more than 178 species of theworld’s largest mammals, those of at least 44 kg, which corre-sponds roughly to the size of sheep to elephants (Barnosky, 2008).Different hypotheses to explain the Late Quaternary extinction havebeen proposed, from environmental catastrophes (mega drought,rapid cooling or increase in precipitation, volcanic activity, etc.) topredator avoidance (herbivores restricted to nonviable refugia)(Ficcarelli et al., 2003; Koch and Barnosky, 2006; Gonzalez andHuddart, 2007), or even meteorite impact (Firestone et al., 2007).Currently, many scholars see the Sixth Extinction as a total orpartial result of past climatic changes (e.g. Nogués-Bravo et al.,2008; Cosgrove et al., 2010). However, climatic changes led both

cologia Humana i Evolució5 Tarragona, Catalonia, Spain.Navarro).

nd INQUA. All rights reserved.

plants and animal species to move from south to north in times ofgood weather and from north to south during ice ages, via expan-sion/retraction of their populations. Thus, it is usual to find woollymammoths in the Mediterranean region, even in the south of theIberian Peninsula, during the Last Glacial Maximum, ca. 20 ka.Similarly, it is common to find other species adapted to warmerenvironments (such as hippopotamuses, which require the liquidwater of rivers and lakes to survive) in the British Islands andcentral Europe in fair weather periods. Most important is that theextinction of megafauna and other species during the Late Pleis-tocene and Early Holocene times is coincidental and parallel withthe territorial expansion of our species, Homo sapiens, theanatomically modern humans (AMHs). In terms of geological timescale, the spread of AMHs was very fast when compared to othermegafaunal species.

Except in its native Africa, in the other continents H. sapiens canbe considered as an invasive alien species, and in moderntimes � after its exponential demographic increasing since Indus-trial Revolution � as a worldwide pest species. The local extinction(extirpation) of native species due to invasive alien ones has beenrecorded in contemporary plant, invertebrate, and vertebrate

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species (e.g. Vivrette andMuller, 1977; Rodda et al., 1992; Tschinkel,1993). Many megafaunal species of Eurasia and the Americas wasstrongly altered at the end of Pleistocene. Whether any extinctionconnection with this fact is considered or not, this alteration wasundeniably concurrent with the relatively sudden arrival of AMHs.To non-African native fauna, including Neanderthal populations,the AMHs represented an alien, unknown predator/competitor towhich it was not previously adapted.

Neanderthals inhabited a vast geographical area extending fromEurope to western Asia and the Middle East (Fabre et al., 2009).However, Homo neanderthalensis was an European endemicspecies, that survived in restricted areas well after the arrival ofAMHs in Europe, and became finally extinct around 28e24 ka(Finlayson et al., 2006). Making an analogy between thedynamics of the early human population and those of animalpopulations, a mathematical model for the growth and spatialexpansion of the human population was applied (Young andBettinger, 1995). In this model, the effect of competition betweenanatomically modern and archaic humans would be a reduction inthe speed of the population wave as the two populations over-lapped, although in this case the effect would be small due to theprobable advantages that the AMH population had in obtainingfood and adjusting to new environments. Recently, an insightfulstudy on Neanderthal extinction based on demographic ecologyhas been published (Sørensen, 2011).

Early Homo left Africa and colonized Eurasia in successive wavesduring the Quaternary times, adapting to the environment andshowing little ability to influence it. However, the arrival ofH. sapiens to anywhere in the world has led to the systematicdestruction of the environment. Initially dedicated to hunting andgathering, after the Neolithic Revolution our species was dedicatedto breaking up the forests for agriculture and shepherding. Thedisappearance of large species of the biological scene is relativelyeasy of explaining by the enormous capacity of AMHs of massivehunting through the use of advanced technologies. No other specieshas ever developed such a killing potential, to whichmust be addedthe reproductive traits of large herbivores, with a low rate ofreproduction, usually a single offspring per litter, and long inter-birth lapses (Nowak, 1999).

Megafauna have only survived until recent times whereH. sapiens has not been able to populate heavily, basically theAfrican savannahs and rainforests and the Southern Asian rain-forests. On one hand, tropical rainforests are little penetrable, andare not the best places for the survival of our species, so untilrecently they have remained very sparsely inhabited. On the otherhand, the vast African savannahs are areas where human settle-ment, agriculture, and grazing have been historically very limiteddue to be endemic regions of the tsetse fly (Glossina spp.), whichtransmits the deadly sleeping sickness. In prehistoric times,humans probably avoided territories where this disease wasprevalent (Lambrecht, 1964).

2. An integrative Neanderthal extinction working hypothesis

Recent history proves that AMHs are causing the extinction ofmany species all over the world. Until the arrival of our species inEurope, Asia, Australia and finally the Americas, the planet waspopulated by a varied fauna of large mammals. Many largemammals have gone disappearing as our species has been colo-nizing new territories, resulting from continuous demographicgrowth and the ever-present ambition to reach beyond forever.Intraspecific genetic variability is reduced in the megafauna by thesmall number of individuals, and generations in time. With lessernumbers of individuals, more gene pool and genetic variability arerequired for the species’ survival. As a result of the evolution from

herbivorous to omnivorous, hominins behave at times like carni-vores in order to maintain a balanced diet. Against the calm thatherbivores show when grazing or browsing, the access andconsumption of meat produces a state of collective excitementamong social meat-eaters, such as lions, hyenas or wolves, but alsoour species, which despite being a social primate sometimesbehaves as a social carnivore.

It has been suggested that the medium-sized species may havebenefited from the habitat structure promoted by the impact ofmegaherbivores (i.e. species more than 1000 kg as adults) onvegetation (Owen-Smith, 1987). Thus, the cascade of extinctionsthroughout Eurasia and the Americas during the latest Pleistoceneand Holocene times encompassed not only all megaherbivores, butalso many medium-sized mammalian herbivores less vulnerable tohuman hunting pressure (Alroy, 2001). Ecologically, selectivepressures are hypothesized to drive evolution in one of twogeneralized directions: r- or K-selection (Pianka,1970). The term r isa constant representing the intrinsic rate of natural increase(individuals$year�1), and K (frequently called the “carryingcapacity”) is the maximum population size permitted by theenvironment. Typically, r-strategy, “opportunistic” species exploitless-crowded ecological niches, and produce many offspring, eachof which has a relatively low probability of surviving to adulthood.In contrast, K-strategy, “equilibrium” species are strong competi-tors in crowded ecological niches, and invest more heavily in feweroffspring, each of which has a relatively high probability ofsurviving to adulthood. In the case of the medium-sized fossilhuman species, the K strategy (accentuated as in the mega-herbivores) leads them to an irreversible cul-de-sac. This tacticseems to be only useful when the dynamic equilibrium predator/prey is ecologically viable. The arrival of a more efficient allochth-onous either predator or competing species implies the extinctionof the autochthonous one. When H. sapiens arrives as a foreignspecies, the delicate equilibrium of predator-prey co-evolution inthe ecosystem is abruptly broken. As a part of this “destructive” andextinction event, the disappearance of the other Late PleistoceneHomo species (H. neanderthalensis, Homo erectus, Homo floresiensis)should be included. AMHs could have exterminated other homininsin route to world occupation because even slight differences in themortality rates of competing populations will lead to the extinctionof the less competitive one (Zubrow, 1989). Doubtless, their lowreproductive capacity was absolutely influential when competingwith AMHs.

Competition between AMHs and Neanderthals had not beendemonstrated (Stewart, 2004). However, concurrent H. sapiensgeographic expansion appears to have produced direct rivalry thatled to Neanderthal extinction (Banks et al., 2008). The palae-oanthropological record and chronometric data of the Uluzzian‘transitional’ technocomplex layers of Grotta del Cavallo cave(southern Italy) confirm a rapid dispersal of modern humans acrossEurope before the Aurignacian and the demise of Neanderthals(Benazzi et al., 2011). In a model for competition between Nean-derthals and AMHs using a mathematical nonlinear system andradiocarbon re-calibrate speed data, the diffusion coefficient spreadhas been evaluated as 1596 km2/y (Flores, 2011). An example ofpossible Neanderthal-AMH competition for resources is found inthe confined area comprising the Riparo Mezzena Neanderthalrockshelter and the Grotta di Fumane Proto-Aurignacian cave, innorthern Italy (Longo et al., 2012). According to Shea (2003),competitive exclusion by the AMH is the most parsimoniousexplanation for Neanderthal extinction. Diamond (1992, p. 364) hassuggested a “genocidal” competitive exclusion of Neanderthals byCro-Magnons on the basis of the ever-present aggressive humannature. In the opposite direction, Stewart (2007) has consideredNeanderthal extinction as part of the faunal change in Europe

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during Late Pleistocene. This paper presents an integrative workinghypothesis to elucidate the fate of Neanderthals based on theirkilling/predation as habitual part of the competition strategy ofAMHs, and in the context of the wider Quaternary MegafaunalExtinction. In this scenario, it is logical to suppose that sucha competition may have had its complement with the hunting ofNeanderthals. Either killing without consumption or predationwith consumption as part of competition strategy has two advan-tages: a) the less competitors, the more prey; and b) the more prey(including in this category other carnivores), the less competitors.Such a stratagem is not a distinctive human behaviour, but wide-spread among carnivorous mammals when two species are over-lapping (Palomares and Caro, 1999). We are a unique species, but inno way a species separated from the natural world. To prehistorichominins, it was not the same living in the tropical Africa than inthe (seasonal) climates of the middle latitudes. The mid-latitudewinters e with few plant foods e are not easy seasons for humansurvival. Although direct evidence for Neanderthal consumption ofa variety of plant foods has been reported by Henry et al. (2011),meat was most probably the best “passport” for such humansurvival. Among recent foraging peoples, large game and animalfoods in general tend to be most important to human diets in thehigher-latitude environments, whereas gathered vegetable foodsand small game tend to be more important in low latitudes despitethat even some tropical groups may depend to a significant degreeon the hunting of large animals (Kuhn and Stiner, 2006, andreferences therein).

It has been long proposed that the palaeolithic AMH protein dietwas very much diversified than that of Neanderthals, which wouldbe based on meat of large land mammalian herbivores (e.g. Cachel,1997; Richards and Trinkaus, 2009). If this difference in ecologicalniche for food existed, dietary competition between both specieswas avoided. However, Drucker and Bocherens (2004) have sug-gested a similar importance of exploitation of the land resources forNeanderthals and AMHs in Europe. If such a similarity is confirmed,this would lead to the possibility of a direct dietary competitionbetween both species. Bocherens et al. (2005) have pointedNeanderthals to a trophic position as top predators in an openenvironment, with little variation through time and space. More-over, there is increasing evidence that Neanderthals not onlyconsumed meat of large terrestrial herbivores but also small game,birds, fish, molluscs, and plants when available (Hardy and Moncel,2011, and references therein). This would imply that the diet of bothhominins was practically the same. In other words, both specieswould occupy the same ecological foot niche and, as an ecologicalconsequence, when they encountered in a same area this ledunfailingly to the removal of one of the two species from theecosystem.

There is no clear evidence of Neanderthals’ predation by AMHs(i.e. Neanderthal bones with cutmarks associated with lithicindustry pertaining to H. sapiens). However, such a possibility hasbeen suggested from the Aurignacian site of Les Rois in south-western France (Ramirez Rozzi et al., 2009). Consequently, it isnot preposterous to think that AMHs might have been able toconsume Neanderthal individuals in a more or less systematic way.There are indicia of AMH violence against Neanderthals (Churchillet al., 2009). There is also evidence of intraspecific cannibalism inboth species (Defleur et al., 1999; Marlar et al., 2000;Walker, 2001).In a hypothetical case of “reciprocal killing/predation” AMHs vs.Neanderthals, the greater efficiency of the AMH weaponry inconjunction with their distinctive long-distance throwing abilities(Henry et al., 2004; Zhu and Bingham, 2011) would involve thatthe balance get out in favour of our species. On the other hand,if actually AMHs and Neanderthals were distinct biologicalspecies (Currat and Excoffier, 2004; Harvati et al., 2004), a cross

consumption of individuals of both species would not even repre-sent a case of cannibalism sensu stricto. This is independent of thefact that some occasional AMH-Neanderthal interbreed may havehappened, as suggested by latest studies based on morphology(Bayle et al., 2010) and genomics (Burbano et al., 2010; Green et al.,2010). Such a hypothetical interbreed does not invalidate ofconsidering AMHs and Neanderthals as two different species.Similar interspecies breeding has historically happened with othermammals, for instance the grey wolf (Canis lupus) and the coyote(Canis latrans), leading to an introgression of alien genes into bothgrey wolf and coyote populations (Mayr, 1996).

3. Conclusion

The mechanism of Neanderthal extinction is a controversialissue of broad interest among human palaeontologists and evolu-tionary biologists. This extinction should be seen as being a merebranch of the Quaternary Megafaunal Extinction, and it could beexplained by habitual killing/predation of Neanderthals by AMHsas part of their competition strategy. The ecologically K early H.sapiens would exterminate other K species, most of them mega-fauna, including the medium-sized non-sapiens human species. IfAMH have really been a lethal K species to other K ones, we canultimately wonder: Is H. sapiens K for “carrying capacity”, or K for“killer”? Neanderthals were part of the large mammal preypotentially hunted by our species, in the same way that historicallyorang-utans, gorillas and chimpanzees, all members of our owntaxonomic family, Hominidae, still are. Most probably, the samehappened whenever a technologically more evolved Homo speciesoverlapped with another less technologically evolved one. Due totheir histological characteristics, human remains, especially bones,are very much more rarely preserved than those of other mega-fauna. Therefore, although at this time there is no clear evidence ofwidespread slaughter of Neanderthals by AMHs, this could simplybe due to the taphonomical difficulty of preserving human remains.Although at the present stage of knowledge of the archaeologicalrecord, the main assumption of this work (i.e. the Neanderthalkilling/predation as habitual part of the competition strategy ofAMHs) can only be considered as a working hypothesis, whatmakes sense to the suggested explanation of the Neanderthalextinction is a consequence of our behaviour as a carnivorousterritorial and social primate.

Acknowledgments

This work was supported by the SpanishMinistry of Science andInnovation (grants MICINN CGL2010-15326/BTE, and MICINNCGL2009-12703-C03-02/BTE), and the Autonomous Government ofCatalonia (grant GENCAT 2009 SGR 324).We thank P. Palmqvist andanother anonymous reviewer for their comments and suggestionson a previous version of the manuscript.

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