Thin on the Ground

Neandertal Biology, Archeology, and Ecology

Steven E. Churchill

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118590867
• Edition: 1
• Topic: Social Sciences
• Subtopic: Physical Anthropology
• Index: Social Sciences

Thin on the Ground: Neandertal Biology, Archeology and Ecology synthesizes the current knowledge about our sister species the Neandertals, combining data from a variety of disciplines to reach a cohesive theory behind Neandertal low population densities and relatively low rate of technological innovation. The book highlights and contrasts the differences between Neandertals and early modern humans and explores the morphological, physiological, and behavioral adaptive solutions which led to the extinction of the Neandertals and the population expansion of modern humans.

Written by a world recognized expert in physical anthropology, Thin on the Ground: Neandertal Biology, Archaeology and Ecology will be a must have title for anyone interested in the rise and fall of the Neandertals.

Chapter One
Thin on the Ground: Population Density and Technological Innovation

The Neandertals are no more. Their ancestors colonized the cold-temperate zones of Ice Age Eurasia, and over the millennia their lineage evolved technological and physical solutions to the adaptive challenges they faced there. The Neandertals persisted for several hundreds of thousands of years in the varied climates and ecosystems of Pleistocene Eurasia, from bitter cold episodes in which much of Europe was carpeted with open steppe and tundra, to warm interglacials when broadleafed forests extended from the Meditteranean to the Baltic Sea. Arguably, the lineage that gave rise to the Neandertals accomplished the first real human colonization of lands outside of the tropics, and their adaptive success over a half million years or more represents a watershed in the human use of technology to deal with the harsh realities of cold, seasonal environments (Foley 1999). But around 50,000 years before present (Ka BP), modern human populations had begun to encroach on the Neandertal homeland, beginning initially in the Near East, but very soon thereafter moving into eastern and central Europe and spreading westward (Hoffecker 2009; Hublin 2012). By about 32 Ka BP the Neandertals were gone, leaving modern humans in sole possession of their former lands.

There is no shortage of hypotheses as to why the Neandertals went extinct. To some, their extinction had nothing to do with the range expansion of modern humans that was occurring at the same time – the two events were only coincidentally related, or perhaps the dying-off of the Neandertals left vacant space into which expanding modern human populations quickly flowed. Thus to some workers the Neandertals went extinct because the climate got too cold for them (Gilligan 2007), or because of a period of climatic instability in which environments and ecosystems changed faster than they could adapt (Finlayson 2005; Finlayson et al. 2004; Finlayson and Carrión 2007; see also Bradtmöller et al. 2012). To others, it was a reduction in carrying capacity as the climate worsened towards the last glacial maximum, leading to the widespread extinction of many elements of the European Pleistocene fauna – Neandertals included (Stewart 2004, 2007; see also Shea 2008). Still others have suggested that they got fried by increased UV-B radiation from a temporary reduction in the ozone layer (Valet and Valladas 2010), or they were unable to cope with an extended “volcanic winter” brought about by a super-eruption (Fedele et al. 2008; Golovanova et al. 2010: but see Lowe et al. 2012), or they baked in their own skin thanks to mitochondria that leaked heat (Hudson et al. 2008), or they did themselves in with transmissible spongiform encephalopathies, perpetrated by their bad habit of eating one another's brains (Chiarelli 2004; Underdown 2008). To others, the modern human diaspora from Africa was an integral part of the demise of the Neandertals, perhaps as a direct result of competition and competitive exclusion (Flores 1998; Banks et al. 2008; see also Svoboda 2005), or due to some combination of climate change and competition with modern humans (d'Errico and Sánchez Goñi 2003, 2004; Stringer et al. 2003; Jiménez-Espejo et al. 2007; Müller et al. 2011). It has also been suggested that modern human populations, expanding into Eurasia from disease- and parasite-rich tropical areas, may have introduced novel diseases into the Neandertal population (Wolff and Greenwood 2010; see also Sørensen 2011). Direct, violent aggression from modern human invaders (Gat 1999; Hortolà and Martínez-Navarro 2013), with some possible intergroup cannibalism (see Ramírez Rozzi et al. 2009), has also been suggested. What with being fried by the sun, frozen by a volcanic winter, driven crazy by “Mad Neandertal” disease and leaking heat from every cell, while being hunted, sickened, and out-done by Neandertal-hungry modern humans, all while the climate wavered and their habitats shrunk – well, one can imagine that the Neandertals might have welcomed extinction when it came!

From anthropological and ecological perspectives, the hypotheses that posit a role of modern humans in the extinction of the Neandertals are perhaps the most interesting. With only one exception (that being the idea that modern humans were vectors of infectious diseases), all of the hypotheses involving modern humans revolve around the concepts of competition and competitive exclusion – either exploitative competition (where both groups were contending for the same resources), or interference competition (direct, aggressive encounters between groups), or both. Modern humans are ecological dominators (Foley 1999; see also Flinn et al. 2005), with a history of progressively monopolizing the productivity of the ecosystems we colonize, altering their landscapes, and growing our populations to densities unknown in other mammals. One component of the expansion of modern humans out of Africa was a noticeable reduction of the large mammal diversity in the areas into which they moved (a trend which, unfortunately, continues today). Loss of biodiversity following modern human colonization is an empirical reality, regardless of one's opinion on whether the two phenomena are causally related (Martin and Klein 1984; Owen-Smith 1987; Klein 1992; Johnson 2002; Brook and Bowman 2004; Pushkina and Raia 2008). Species that were direct resource competitors with modern humans tended not to fare well (Chapter 9: Berger 1999), and thus we might see the extinction of the Neandertals as part of a larger Late Pleistocene, modern human-mediated alteration of the mammalian communities of Eurasia (Stewart et al. 2003; Stewart 2007). Seen in this light, the demise of the Neandertals might best be seen as an integral part of our own story.

If Neandertal extinction was mainly due to competition with modern human invaders, it would imply that the latter had a competitive advantage over the indigenous Neandertals. This in turn raises the interesting question as to how modern human newcomers to the Ice Age environments of Eurasia were able to outcompete a group of hominins that were seemingly well-adapted to those environments (given that they and their ancestors had successfully survived there for a half million years or more), an argument that many find troubling (see for example, Finlayson et al. 2004). Recent human history is certainly replete with cases of invading colonists replacing indigenous peoples, but in these instances infectious disease ecology and technological superiority (coupled with a demographic advantage) are generally invoked to explain the ultimate demise of the native populations (Diamond 1997). Because the post-50 Ka BP incursion of modern humans into the Near East and Europe is attended by the first appearance of Upper Paleolithic assemblages (whereas the local Neandertals were still largely or entirely using Middle Paleolithic toolkits: see Chapter 3.1), it is natural to think that differences between the two groups in technological sophistication may have played an important role in the competitive dynamics between them. Consistent with this idea is the observation that, in artifact assemblages associated with modern humans, rates of technological innovation have steadily accelerated over the last 75,000 years of our evolution (another trend which continues today), whereas the technology of the Neandertals remained largely unchanged (from the perspective of innovation) over hundreds of thousands of years.

Beginning sporadically in the later part of the Middle Stone Age (MSA) and continuing with increasing regularity into the Later Stone Age (LSA) and Upper Paleolithic (UP), modern human-associated assemblages¹ document a rapid florescence of new technologies, including leptolithic and microlithic tools, greater artifact diversity, bone and antler working, heat treatment and pressure flaking of flint, long-range projectile weapons, grindstones, fishing and birding gear, trapping technology, sophisticated pyrotechnology, and possibly watercraft (Valde-Nowak et al. 1987; Mellars 1989a, 1989b; Straus 1991, 1993; Davidson and Noble 1992; Brooks et al. 1995, 2005; Yellen et al. 1995; Henshilwood and Sealy 1997; Ambrose 1998a; Holliday 1998; McBrearty and Brooks 2000; Henshilwood et al. 2001; Shea 2006; d'Errico and Henshilwood 2007; Backwell et al. 2008; Brown et al. 2009; Villa et al. 2009b: Lombard and Phillipson 2010; Mourre et al. 2010). Also during this period we begin to see increasing evidence of symbolic behavior and abstract thought, in the form of pigment processing, personal adornment, incised notational pieces, musical instruments, and mobilary and parietal art (McBrearty and Brooks 2000: Henshilwood et al. 2002, 2004, 2009; Conard 2003, 2009; d'Errico et al. 2005, 2009; Bouzouggar et al. 2007; Marean et al. 2007; Broglio et al. 2009; Conard et al. 2009; Higham et al. 2012). Furthermore, modern human-associated faunal and lithic assemblages from the late MSA onwards provide evidence for expanded diet breadth and innovations in subsistence strategies, expanded social networks, and long-distance exchange (McBrearty and Brooks 2000; Bar-Yosef 2002; Henshilwood and Marean 2003). Together these behaviors – from technological innovation to symbolic expression to niche expansion to enriched social complexity – signal the emergence of what has been called “behavioral modernity” or “fully symbolic sapiens behavior” (Henshilwood and Marean 2003; Nowell 2010).

The technological explosion that occurred coincident with the modern human diaspora reflects a notable aspect of our behavior, that being our extraordinary capacity for cumulative technological evolution (CTE), or “cultural ratcheting” (Tennie et al. 2009). This is the process by which multiple actors, who may be well-separated in space and time, contribute innovations towards the development of a single piece of technology or a technological system. Using the development of projectile weapon systems as an example, one individual might have loosely tied feathers to the proximal end of a spearthrower dart to develop the first fletching, and the attendant improvement in flight performance might cause this innovation to catch on and spread. Decades later and miles away, another individual might have devised a better way of binding the feathers to the shaft to further improve flight performance. Cultural ratcheting seems to be a component of modern human technological behavior from Marine Isotope Stage (MIS) 4 onwards, whereas it does not appear to have characterized the Neandertals' relationship to technology. Neandertal-associated Middle Paleolithic material culture, while dynamic and flexible in its own right, seems to lack the regular innovation of tool forms and new ways of using material items for symbolic expression that are seen in modern human-associated assemblages (this is not to say that innovation is totally lacking in Neandertal material culture, just that it is relatively rare: see below). The Neandertals certainly weren't stupid (their brains were every bit as large as ours, and in fact were a little larger on average: Chapter 4), and they and their ancestors had the adaptive wherewithal to survive the rigors of Ice Age Europe for more than 500,000 years. Why, then, this dramatic difference in technological acumen between two closely genetically related, behaviorally-flexible, ecologically-similar human groups?

The apparent technological dichotomy between Neandertals and early modern humans suggests to some that there were important cognitive differences between groups, and that Neandertals may have lacked the capacity for innovation, planning depth, abstract thought, and symbolic behavior that underlies behavioral modernity (see McBrearty and Brooks 2000). Since increased CTE and the geographic expansion of modern humans out of Africa occurred roughly 100–150 Ka after their earliest appearance in the fossil record (White et al. 2003; McDougall et al. 2005), this would suggest that the earliest modern humans likewise lacked the capacity for modern behavior. The persistent expression of symbolic behavior, as well as the marked acceleration of CTE, does not appear to be firmly established until the development of the LSA (in Africa) and UP (in Eurasia) sometime around 50 Ka BP (Klein 2000, 2008; Bar-Yosef 2002; Mellars 2006b; Nowell 2010). This has led some to argue that behavioral modernity resulted from an upgrade in cognitive abilities at around 50 Ka BP, perhaps reflecting a relatively rapid appearance and fixation of new alleles governing neural development (Mellars 2006b). Different cognitive enhancements have been proposed as being key to the emergence of modern behavior, including enhanced working memory (Wynn and Coolidge 2004, 2010; Ambrose 2010), domain-sharing intelligence (Klein 1995), linguistic and symbolic capacities (Mellars 1989b, 2007; Klein 2000, 2003), abstract thinking (Lewis-Williams 2002), “latching” (Amati and Shallice 2007), and the ability to attain higher levels of intentionality (Dunbar 2003).

There are, however, compelling reasons to suspect that Neandertals had cognitive and behavioral capabilities that were on a par with those of the early modern human makers of the LSA and UP. As noted above, their brains were every bit as large as those of early modern humans. There is also growing evidence that Neandertals had the cognitive capacity for substantial technological innovation (Gaudzinski 1999; Villa and d'Errico 2001; Hardy et al. 2013; Soressi et al. 2013), and that they were fully able to engage in symbolic behavior (Zilhão et al. 2010; d'Errico and Stringer 2011; Caron et al. 2011; Peresani et al. 2011). These findings imply that the critical difference between Neandertals and modern humans, and also between modern humans before and after 50 Ka BP, was not in cognitive capacity, but rather in the prevalence and persistence of technological innovation and symbolic behavior.

Increasingly, archeologists and cognitive psychologists are examining the role of cultural, historical, ecological, and demographic factors in both CTE and the persistent expression of symbolic behavior. There is a growing school of thought that holds that the capacity for modern behavior may have emerged at the same time that anatomical modernity did (that is, coincident with the first appearance of modern humans some 200–150 Ka BP), or possibly before (and thus is perhaps a shared primitive trait [symplesiomorphy] that both Neandertals and modern humans inherited from a common ancestor), but that social and demographic factors prevented its consistent expression until the end of the MSA (Chase 2006; Jacobs and Roberts 2009; Nowell 2010; d'Errico and Stringer 2011). Demographic expansion and population density especially are increasingly thought to have played a central role in the expression of behavioral modernity (Jacobs and Roberts 2009; Richerson et al. 2009). Cultural ratcheting requires both cultural innovation and transmission, and variation in these processes is conditioned by the rate of interaction between social learners (Shennan 2001; Henrich 2004). The absolute number of innovators, and rates of technological transmission, are dependent on population size and structure. When population density is low, innovations may arise but their rate of transfer to other groups is generally insufficient to offset the stochastic loss of cultural knowledge that occurs as individuals or local groups die off, and the low relative abundance of technologically-talented individuals combined with the dynamics of social learning may result in a reduction in average technological skill levels in a group over time (Henrich 2004). Computer modeling (Shennan 2001; Powell et al. 2009) and analyses of cultural complexity in small-scale societies (Henrich 2004; Kline and Boyd 2010) both show that populations with either large overall size or high connectedness between subpopulations are more successful in generating, retaining, and diffusing cultural innovations. Thus the sporadic occurrences of symbolic behavior and technological innovation in the earlier part of the MSA (McBrearty and Brooks 2000) may represent geographically-restricted, transient peaks in population density (in which CTE begins to take off) followed by demographic crashes (possibly caused by downturns in climate) (Mellars 2006a; Jacobs and Roberts 2009; Powell et al. 2009; Richerson et al. 2009). Similar transient increases in Neandertal population densities may account for the irregular manifestation of technological innovation and symbolic expression in the European Mousterian. Later expansion of modern human populations in Africa around 80–70 Ka BP, and their subsequent demographic expansion into Eurasia between 60–40 Ka BP (Watson et al. 1997; Excoffier and Schneider 1999; Stiner et al. 1999; Forster 2004; Steele and Klein 2005) seem to have produced population densities sufficient for a high rate of CTE. Thus it may have been demographic factors, rather than cognitive capabilities, that account for the persistent expression of behavioral modernity in the LSA and UP (Shennan 2001; Powell et al. 2009).

When viewed in this light, the technologically-mediated competitive advantage of early modern humans which may have allowed them to supplant native archaic human populations (such as the Neandertals) across the Old World may have been an epiphenomenon of population growth. The Neandertals, on the other hand, appear to have lived at relatively low population densities throughout their tenure. The relatively small metapopulation size of the Neandertals would have impeded CTE and promoted culture loss, while at the same time making the Neandertals vulnerable to extinction even before modern humans reached Eurasia.

The chapters that follow advance two mutually compatible arguments as to why the Neandertals lived at such low population densities – that is, why they were so “thin on the ground.” First, consideration of the Neandertals' adaptive solutions to environmental and ecological challenges shows that these solutions were effective but energetically costly (for example, Neandertals had bodies that were good at producing heat: turning up the furnace is an effective way to maintain a constant body temperature in the cold, but it is more costly than adding insulation). The nature of these adaptations resulted in a high energetic overhead to Neandertal life in Ice Age Europe, and the high cost of somatic maintenance and foraging resulted in Neandertal energy budgets that were very tight. This constrained the extent to which Neandertals could store energy as fat (making them “thin on the ground” in another sense), and constrained the amount of energy that could be invested in reproduction. As a consequence, Neandertals likely had a difficult time attaining the levels of fertility needed for population growth. Indeed, given what appears to have been high adult mortality, even reproduction sufficient for the maintenance of stable populations may have been a challenge for the Neandertals at some times. Second, consideration of the behavioral ecology of the Neandertals' resource competitors – members of the Eurasian later Pleistocene large mammal carnivore guild – suggests that Neandertal population growth may have also been ecologically constrained. Consideration of the size, social organization, and behavior of the various carnivore species of Pleistocene Eurasia, as well as what we can infer about Neandertal weapon ...