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The Human Nature Review 2002 Volume 2: 156-163 ( 1 May )
URL of this document http://human-nature.com/nibbs/02/frost.html
Desolate Landscapes: Ice-Age Settlement in Eastern Europe
By John F. Hoffecker
New Brunswick, Rutgers University Press: 2002
Reviewed by Peter Frost, Groupe d’études Inuit et circumpolaires, Université Laval, Quebec, Canada, G1K 7P4.
As humans spread out of Africa, they entered new environments, including one that no longer exists. The loess-steppe covered the East European Plain off and on during successive ice ages until 10,000 years ago. Quite unlike today’s northern barrens, it combined Arctic tundra with fertile loess soil and low latitudes―the Eurasian tundra belt having been pushed far to the south by the Scandinavian icecap. Long intense sunlight favoured a lush growth of mosses, lichens, grasses, and low shrubs that fed mammoths, reindeer, bison, and horses. Despite this high bioproductivity, the loess-steppe confronted humans with a number of adaptive challenges. Winter temperatures averaged from -20 to -30 °C in exposed conditions with little natural protection. Wood was scarce for fuel or shelter. Finally, almost all of the biomass suitable for human consumption was in the form of large migrating mammals.
Early humans were in Europe as early as 800,000 BP but they lacked specific cold adaptations, apparently spreading into the continent during warm interglacials and retreating once ice-age conditions returned (pp. 36-38). With the Neanderthals (200,000 - 30,000 BP), we see the first humans who could stand the cold, as shown by their high volume to surface ratio (short limbs, short fingers, broad chests) and their presence in Europe during the Early Pleniglacial ice age (71,000 - 55,000 BP) (p. 55-60). They could also tolerate a high-protein meat diet, as indicated by stable isotope analysis of Neanderthal bones (p. 109).
The Neanderthals could not, however, colonize the loess-steppe of the Early Pleniglacial, a period that corresponds to a gap in the stratigraphy of their sites on the East European Plain (p. 65). This absence stemmed from their failure to develop technologies for open Arctic environments (pp. 107-109). Artificial shelters seem to have been limited to windbreaks or simple lean-tos. Microwear analysis of stone tools indicates that hides were worked, but only for the initial phases of hide preparation. The absence of eyed bone needles, so common at modern human sites, suggests that hides were used as blankets or ponchos, and not tightly sewn together to make tailored clothing. Fires were made and tended, but hearth analysis reveals the fuel to have been mainly wood, a scarce material on the loess-steppe. Finally, there is no evidence of untended traps or permafrost pits for cold storage. The Neanderthals thus failed to colonize the loess-steppe even though they survived the Early Pleniglacial in environments just as cold and had been in Europe for over 100,000 years.
In contrast, modern humans colonized the loess-steppe of the Last Glacial Maximum (25,000-13,000 BP) less than 20,000 years after they entered Europe, despite a physique essentially adapted to warm climates. They overcame their physical handicap through technological innovations: production of tailored clothing, as attested by numerous needles and awls and by evidence of pelt removal from fur-bearing animals; construction of artificial shelters with interior hearths; use of bones as fuel; and digging of “ice cellars” into the permafrost for storage of meat and bones (pp. 158-162, 217-233).
Advent of Symbolic Thinking
These innovations required an ability to manipulate not only objects but also mental representations of objects, e.g., by calling up images stored in the mind for use as “templates” in tool manufacture and shelter construction, by imagining scenarios of possible courses of action, by memorizing spatial and temporal relationships, etc. We see this aptitude most clearly in the finely detailed representational art (figurines, engravings, paintings) that is so abundant at modern human sites and virtually absent at Neanderthal ones (pp. 174-177). But we also see it in evidence of long-distance transport and extensive social networks that required a capacity to think ahead over space and time (pp. 184-185).
Hoffecker calls this ability “symbol-based technology” and ascribes it to a shift from domain-specific cognition to general intelligence (p. 12). In domain-specific cognition, symbols exist in the mind within fixed configurations that mediate a specific response to a specific situation. They cannot be rearranged, nor can they be exchanged with other individuals. In domain-general thinking, symbols can be freely rearranged within the mind to represent any situation, real or imaginary. It thus becomes possible to imagine different responses to a situation and then choose the one that produces the best outcome. Furthermore, by converting mental symbols into speech, different individuals can collectively develop a shared response, thereby broadening the pool of information for decision-making.
This change in mental organization―and not in anatomy―marks the advent of modern humans. It is true that anatomically modern humans existed as early as 130,000 BP if not earlier. These early moderns, however, were technologically no different from the Neanderthals and were limited to a specific environment, spreading out of Africa into the Levant as the climate warmed during the Last Interglacial and retreating as it cooled during the Early Pleniglacial. They are better described as “almost moderns”―an evolutionary side-branch closely related to us but possessing a neural organization closer to that of archaic humans (p. 141).1 Modern humans probably arose in a later demographic expansion that spread out of Africa some 50,000 years ago, this time bringing humans endowed with general intelligence.
Replacement or Intermixture?
What ensued is a matter of debate. Did modern humans replace the Neanderthals or did the two intermix? Hoffecker leans to the replacement model. In Eastern Europe, the latest Neanderthals show no modern human features and the earliest modern humans show no Neanderthal features (p. 157). Furthermore, mtDNA analysis of a late Neanderthal from the Caucasus indicates little if any genetic exchange with modern humans (p. 158).
The picture is less clear when we look at cultural artifacts from this transitional period (40,000 - 25,000 BP). Some East European sites yield Upper Paleolithic assemblages that are typical of modern humans. Others yield Upper Paleolithic assemblages intermixed with Mousterian assemblages that are typical of Neanderthals. Finally, some yield Mousterian assemblages with low percentages of Upper Paleolithic tools and artifacts (pp. 160-162). Like the Chatelperronian industry of Western Europe and the Szeletian industry of Central Europe, these sites argue for some kind of cultural contact between modern humans and Neanderthals. Perhaps the latter traded hides for tailored clothing and ornamental items. This contact period would have ended with the return of ice-age conditions c. 25,000 BP: on the one hand, the Neanderthals had withdrawn from what was becoming loess-steppe; on the other, modern humans had made enough cold adaptations to survive on their own.
One objection to the replacement model has come with the discovery of a Portuguese skeleton that dates to 24,500 BP, is mosaic in appearance, and raises the possibility of some intermixture between modern humans and Neanderthals (Duarte et al. 1999). It is one thing, however, to say that intermixture occurred. It is another to say that it had lasting consequences. Some acculturated Neanderthal groups may have intermixed extensively and yet have still been marginalized and replaced as modern humans grew in numbers. There is little sign of anything but modern humans in the current gene pool, at least if we look at mitochondrial DNA. The estimated age of European mtDNA lineages goes no further back than 50,500 BP (Richards et al. 1996). As well, mtDNA and dental traits show the Neanderthals to be no closer to present-day Europeans than they are to any other modern human population (Krings et al. 1999; Ovchinnikov et al. 2000; Tyrell and Chamberlain 1998).
While acknowledging that mtDNA supports replacement, Templeton (2002) argues that several nuclear DNA polymorphisms are much older than the expansion of modern humans out of Africa and must therefore reflect intermixture with Neanderthals and other archaic humans. Templeton’s analysis suffers, however, from two flaws: (1) a wide margin of error in the time estimates based on nuclear DNA polymorphisms, combined with a bias in favour of polymorphisms that look older than they really are; and (2) a disregard for selection pressures that would inflate the variability of these polymorphisms and thereby inflate the time estimates.
As Templeton himself concedes, nuclear DNA accumulates variability at a slower rate than does mtDNA, so any time estimates would suffer from a wider margin of error. Although this may explain why some polymorphisms yield very old dates (oldest = 1.9 million BP), it is not readily apparent why none yield very young ones (youngest = 230,000 BP). Keep in mind that if a polymorphism looks much younger than its real age it would also have much less variability. A significant proportion would have none at all or not enough to attract the interest of population geneticists. Templeton is thus using a biased sample that includes polymorphisms that have much more variability than they should for their age but excludes many that have much less.
The second flaw is that all but one of Templeton’s nine nuclear DNA loci produce proteins of one sort or another. They are thus exposed to selection pressures that may inflate genetic variability, i.e., through heterozygote advantage, frequency-dependent sexual selection, disease-resistance polymorphisms, and other balanced polymorphisms. Templeton uses the hemoglobin β-chain locus in his analysis, yet many of its alleles (e.g., β-Thalassemia) are clearly balanced polymorphisms that provide some protection against malaria. The MC1R locus is used even though its alleles code for highly visible differences in hair colour that may have been maintained through sexual selection (Rana et al. 1999). The PDHA1 locus is used, yet different portions of the PDHA1 region have evolved at different rates, a strong indication of natural selection (Disotell 1999). The MX1 locus is used even though one of its alleles causes alopecia areata in the homozygous state and is likely maintained through some form of heterozygote advantage (Tazi-Ahnini R et al. 2000).
Male Provisioning, Polygyny Constraints, and Sexual Selection
In any case, there was no replacement or intermixture on the loess-steppe. Modern humans were moving into an environment that no other Homo had successfully colonized. To overcome the challenges of the harsh Arctic climate, they created new forms of fuel, clothing, and shelter. To overcome the challenges of a different food supply, they reallocated the tasks of food procurement between men and women. This shift in food procurement is evident if we compare present-day hunter-gatherers from the Tropics and the Arctic. In the tropical zone, men hunt while women gather berries, fruits, roots, grubs, eggs, and other sessile food items, these tasks being more compatible with the demands of pregnancy, breast-feeding, and infant transport (Kelly 1995:268-269). Further north, food gathering is limited by the long winter, providing less than 10% of all food among hunter-gatherers above 60° N, as compared to 40-55% below 40° N (Martin 1974:16-18). The end point of this trend is Arctic tundra, where almost all of the available biomass is in the form of game animals. Such environments compel women to process food obtained through hunting instead of gathering food on their own.
Hoffecker discusses the implications (p. 8). First, “hunter-gatherers in northern continental environments who subsist on terrestrial mammals must forage across large areas in order to secure highly dispersed and mobile prey.” Second, “[a]nother consequence of low temperatures and a high meat diet is that males procure most or all food resources.”
This change in the sexual division of labour would have had demographic and, ultimately, evolutionary consequences. As hunters cover longer distances, they increase their risk of death from starvation, accidents, or inclement weather, a risk that is already high because they carry a minimum of supplies for sustenance and shelter. If we look at present-day Arctic groups with no herd dogs or domesticated reindeer (e.g., the Chukchi), male mortality rises sharply with hunting distance (Krupnik 1985). In addition, hunting is more hazardous in the Arctic because of the extreme weather and the relative absence of alternate food sources for hunting parties. There thus develops a male deficit in the sex ratio. Among 19th century Labrador Inuit, the 15+ age bracket had only 57 males for every 100 females (Scheffel 1984).
Few of the excess women, however, can become second wives. This is because of the high demands on male provisioning. In his review of Inuit mating systems, Kjellström (1973:118) concludes, "Since the duty of being a provider was more onerous for the man who had two or more wives, this meant that as a rule it was only the really able and skilful hunters and fishers who could manage this double duty." Together, these two factors-high male mortality and limited polygyny-skew the operational sex ratio towards a female surplus, thereby causing women to compete more intensely for mates. One result is an intensification of sexual selection.
Sexual selection is not unusual in itself, but it usually acts more on males than on females. All things being equal, more males than females are available for mating at any point in time, given the latter’s unavailability during pregnancy and early infant care. If, however, a population has more females than males and if polygyny is constrained, we have the conditions for a reversal of the usual pattern.
Nonetheless, this potential for sexual selection has to contend with a third factor. Female infanticide used to reduce the excess of women over men in Arctic hunter-gatherers living at high latitudes, like the Inuit of Canada’s High Arctic. The population density being very low, parents were reluctant to raise a daughter who would probably marry out of the band and not support them in their declining years, either directly or through her future husband (Smith and Smith 1994). In the Low Arctic, higher population density increased the likelihood of “son-in-law payback”; consequently, the Inuit practised much less female infanticide at lower latitudes (Schrire and Steiger 1974). If we extrapolate this trend to the loess-steppe, where high bioproductivity supported higher population densities than those of present-day Arctic groups, it is likely that female infanticide would not have “corrected” the excess of women over men.
If humans experienced intense sexual selection on the loess-steppe, were there evolutionary consequences? One may be the diverse eye and hair colours we see in a zone centred on the East Baltic and covering most of Eastern and Northern Europe. Within this zone, eyes may be not only brown but also blue, grey, hazel, or green, while hair may be not only black but also brown, flaxen, golden, or red (Beals and Hoijer 1965:212-214). In the absence of selection pressures, the current level of hair colour diversity would have taken 850,000 years to develop (Templeton 2002). One would have to conclude that the gene pool of Eastern and Northern Europe is derived mainly from the Neanderthals and even earlier Homo populations. Otherwise, some kind of selection must have favoured these colour polymorphisms.2
Sexual selection has already been advanced as an explanation (Cavalli-Sforza et al. 1994:266). If faced with an abundance of equally suitable mates, the sex in short supply will select a mate that “stands out from the crowd” in having, for example, a rare and highly visible colour morph. Such selection is frequency-dependent, declining in strength as the rare morph becomes more common and tending towards an equilibrium that maximizes colour diversity (Endler 1980; Keegan-Rogers and Schultz 1988). Colour polymorphisms due to sexual selection have been reported from insects, fishes, and birds (Keegan-Rogers and Schultz 1988). There seem to be two preconditions: (1) a low level of predation, because brightly coloured traits facilitate prey detection; and (2) an absence of related species sharing the same geographic range, apparently because too much intraspecific variability interferes with species recognition (Endler 1980). Both preconditions were probably met by modern humans: predation was a minor cause of mortality and species recognition had become less problematical with the disappearance of the Neanderthals.3
1. This view is supported not only by their material culture but also by archaic skeletal features that are absent in later modern humans (Kidder et al. 1992; Pearson 1998).
2. Hair-colour diversity is due to different alleles at the MC1R locus: Europeans have 13 nonsynonymous (phenotypically distinct) alleles, Asians have 5, and Africans 1 (Harding et al. 2000). Furthermore, the Asian nonsynonymous alleles appear to differ little in their phenotypic effects (Harding 2001). Eye-colour diversity is due to alleles at another locus although there may be some linkage between brown hair and green eyes (Eiberg and Mohr 1987).
Harding et al. (2000) attribute Europe’s high MC1R diversity to relaxation of selection for dark skin outside the tropical zone. This would account for the redhead alleles, which are linked to skin depigmentation, but not for the other hair colour alleles, which are not linked. Relaxed selection would also fail to explain the low MC1R diversity at non-tropical latitudes in Asia. In their article, Harding et al. (2000) advance three arguments for relaxation of selection, as opposed to positive selection for hair colour diversity. First, they argue that relaxed selection has produced a comparable level of diversity at the b-globin locus. Yet b-globin variants clearly have selective value, as indicated by evidence of heterozygote advantage and the short time-span (less than 5,000 years) over which the b-globin polymorphism has evolved (Cavalli-Sforza et al. 1994: 149-152). Second, the authors argue that the ratio of nonsynonymous (phenotypically distinct) to synonymous (phenotypically indistinct) alleles is only 10 to 3 in Europe and thus comparable to the ratio of 10 to 6 for the MC1R substitutions that separate humans from chimpanzees. The data in table 1 of their article, however, indicate a ratio of 13 to 2 in Europe (the 2 redhead alleles are excluded because they come from a study that specifically looked for them and the human consensus sequence is misassigned as a synonymous allele). In any case, given the selective value of coat colour in other primates, it would be erroneous to use the 10 to 6 ratio separating humans from chimpanzees as a benchmark for absence of selection. Third, the authors argue that MC1R diversity does not depart significantly from the Hardy-Weinberg equilibrium, there being neither excess homozygotes nor excess heterozygotes. No such departure, however, would be expected, since MC1R heterozygotes exhibit partial effects (Flanagan et al. 2000; Preston 2001; Rees 2000).
As Rana et al. (1999) have observed, the human MC1R gene is unusually polymorphic, both in its number of alleles and in its ratio of nonsynonymous to synonymous alleles. At most gene sites, synonymous alleles outnumber nonsynonymous ones. The MC1R gene shows the opposite pattern, being five times more likely than others to have alleles at nondegenerate sites and two times more likely to have alleles at fourfold degenerate sites (see also Preston 2001).
3. The loess-steppe had only two predators that may have preyed on humans: wolves and bears, the latter being uncommon (pp. 238, 240). Present-day Arctic hunter-gatherers suffer only occasional predation by wolves.
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Frost, P. (2002). Review of Desolate Landscapes: Ice-Age Settlement in Eastern Europe by John F. Hoffecker. Human Nature Review. 2: 156-163.