Holocene boundary in northern South America

PERGAMON

Quaternary International53/54 (1999) 3 9

An archaeological perspective of the Pleistocene/Holocene boundary in northern South America Crist6bal Gnecco Departamento de Antropologia, Universidad del Cauca, Apartado Akreo 755, Popay~n, Colombia

Abstract

In this paper, I examine Late Pleistocene/Early Holocene adaptations of hunter-gatherers to different ecosystems in northern South America. The role played by the climatic events associated with the Pleistocene/Holocene boundary in the evolution of culture in that part of the Americas is assessed in the light of those adaptations. The conclusion is that the Pleistocene/Holocene boundary is not very useful in understanding the human process of early colonization and adaptation to the various ecosystems of northern South America, because a mechanism of cultural change cannot be linked to that boundary. © 1998 INQUA/Elsevier Science Ltd. All rights reserved.

1. Introduction

It is instructive to ask whether the Pleistocene/Holocene boundary in the Americas, widely accepted to fall at ca. 10,000 BP (e.g. Van der Hammen, 1974:10-11), marks a real event or is merely an arbitrary limit set up by earth scientists and archaeologists. If it is arbitrary, it should have philosophical utility; otherwise, we can easily discard it. Arbitrary constructions, of which scientific praxis is so fond and so full, must necessarily be assessed on the basis of utility. If this boundary represents concrete events, the facts providing the fuel for the division ought to be clear. Earth scientists would answer that the chronological boundary dividing the Pleistocene from the Holocene indicates real events, and they would do so with heavy ammunition. The frontier neatly divides the last Glacial from the Interglacial in which we currently live. Data supporting this interpretation, including pollen and deep-sea cores, are numerous (e.g. Webb et al., 1993; Williams et al., 1993). Although it could be argued that the climatic changes occurring between 7000 and 5000 BP (mid-Holocene by standard convention) were as dramatic as those that occurred immediately following the end of the Pleniglacial (Tardiglacial or Late Glacial by standard convention), we can still say that the factual evidence does not undermine the validity of the limit. Instead, another limit would be needed (perhaps one dividing the Holocene in two halves). Nevertheless, the Pleistocene/Holocene frontier in fact distinguishes

climatic events of large magnitude, events that deeply affected the composition of most ecosystems. American archaeologists, however, would not be as comfortable facing the question. On the one hand, the old clear-cut, pan-continental division between Paleoindians (specialized big-game hunters) and the Archaic (generalized foragers), that was based on a presumed causal correlation seen to exist between the end of the Pleistocene, the extinction of megafauna, and the correspondent adaptive shift at the beginning of the Holocene, is no longer tenable (e.g. Bryan, 1973, 1986; Meltzer and Smith, 1986; Dillehay et al., 1992; Meltzer, 1993). In addition, archaeologists simply do not yet understand how the climatic changes at that time affected human adaptations, especially on a continental scale. In fact, the Paleoindian-Archaic transition has been the subject of careful scrutiny in the last two decades. New evidence encountered in several American sites dating to around 10,000 BP or earlier has led to a reconsideration of the transition. That evidence points to a diversity of Late Pleistocene adaptations to different ecosystems associated with a considerable cultural variability, showing a pattern of generalized gathering and opportunistic hunting (cf. Bryan, 1978, 1986; Bonnichsen and Turnmire, 1991; Dillehay et al., 1992). A specialized hunting economy also may have been occasionally possible, but only where sufficient and reliable animal biomass was available - - the exception, not the rule. Therefore, if the specialized-generalized shift ever really happened in the Americas, it was only regional, such as in

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the Great Plains of North America, and never on the scale of a whole continent. Even this possibility is disputed, however (cf. Meltzer and Smith, 1986). If the cherished, posited causation between post-glacial ecosystemic rearrangements responsible for the extinction of megafauna and the Paleoindian-Archaic transition has to be abandoned as a general principle. then the impact of those rearrangements in human populations must be reassessed. Two possibilities exist: either we keep looking for a different correlation on a continental or even global scale: or we devote our efforts to understanding how Late Glacial and post-glacial climatic events affected human populations at the regional level. The former approach is in vogue with the processual goal of establishing general laws, but it may be a dead end. The latter may be more fruitful, but it may force us to lose control of the big picture. Alternatively, we have overestimated the impact of post-glacial climatic phenomena on humans. Future research may reveal that other variables, largely ignored until now, were more determinant in the unfolding of the events that followed the almost pan-continental shift away from hunting and gathering as a successful way of life. Here, however, I assume for the sake of discussion that climatic events resulting in ecosystemic changes really have an important bearing in the evolution of culture. More specifically, 1 will examine what was the role, if any, played by the climatic events associated with the Pleistocene/Holocene boundary in the unfolding of sedentarism, agriculture, and complexity in northern South America. 1./. The archaeological record The available archaeological evidence indicates that human beings were exploiting open areas in northern South America as early as the Late Pleistocene. Near the city of Coro, in the arid coast of Venezuela, several sites have been found (refer to Fig. 1 for the location of the regions mentioned in this article) providing evidence of the association of El Jobo projectile points with extinct fauna as far back as 13,000 BP (Cruxent and Rouse, 1956: Rouse and Cruxent, 1963; Bryan, 1973; Bryan et al., 1978: Ochsenius and Gruhn, 1979). In what is now the arid Santa Elena peninsula in Ecuador, Stothert (1985, 1988t has found evidence of early occupations, initially based on broad-spectrum hunting-gathering and progressively oriented to marine resources, located in formerly rich maritime-riparian-inland ecotones. The dates of these exploitations presumably range from 11,000 to 6600 BP. In the middle Orinoco river basin, Barse (1990) has uncovered at least one occupation dating to the Early Holocene and associated with unifacial stone tools. This occupation seems to have occurred in a forest/savanna environment. L6pez (1992) has found substantial evidence for a Late Pleistocene-Early Holocene occupation

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75

80

!

/

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+

1 VENEZUELA

5 SABANA DE BOGOTA

2 SANTA ELENA

6 CALIMA

3ORINOCO

7 ARARACUARA

4 MAGDALENA

8 POPAYAN

Fig.

l.ocation of the regions mentioned.

of the semi-arid Magdalena river valley in Colombia, including Paijfin-like projectile points. Evidence for human occupation of diverse tropical forests is much more abundant, and in some cases is well organized in regional sequences. However, the most abundant evidence has been obtained in high mountain forests. The archaeological sequence established for the Sabana de Bogot& in the eastern highlands of Colombia, is the most complete and best documented regional sequence of the northern Andes, spanning from about 12,000 BP to the appearance of agriculturists some 3000 years ago (e.g. Correal and Van der Hammen, 1977; Hurt et al., 1977: 14; Correal, 1981, 1986). Although there were significant variations in ecosystemic composition since the last glacial, fine-tuned paleoenvironmental reconstructions point to a dominance of forested formations in the areas of human occupation throughout the last 13,000 years (cf. Van der Hammen and Correal, 1978). There is evidence of human occupation in the upper and middle Calima valley by 10,000 years ago in a forested formation. The data are meager, but they indicate a simple, persistent technology (Cardale, 1992). There is also evidence of hunter-gatherer adaptations to a tropical mountain forest in the valley of PopayAn, in southwestern Colombia, where bifacial, unifaciat, and grinding tools have been uncovered along with abundant charred vegetal material at San Isidro (Gnecco, 1994). Although there is sparse evidence indicating that the

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tropical lowlands may have been occupied since the Late Pleistocene (Correal, 1977; Reichel-Dolmatoff, 1987: 47), recent data indicating occupation dating to 9000 BP has been obtained from a terrace of the Caquet~ river in the Colombian Amazon (Cavelier et al., 1995). Here, a preceramic occupation characterized by unifacial tools and the exploitation of vegetal resources with grinding artifacts occurred in a tropical rain forest. While this evidence clearly shows a great variety of Late Pleistocene/Early Holocene adaptations, ruling out the old Paleoindian (specialists)-Archaic (generalists) dichotomy, it is necessary to consider if there are really identifiable patterns in the events which eventually led hunter-gatherers to agriculture, village life, and complexity. To begin with, it is clear that those events happened for the most part in the Holocene, a time in which demographic trends apparently culminate in zonal overpopulation and territorial impingement in a previous Pleistocene landscape of large territories occupied by highly mobile but rather small groups. To be sure, climatic changes and ecosystemic reorganizations occurred many times during the Pleistocene, some of them of greater magnitude than the changes of the post-glacial. But it is only from the post-glacial onwards that the definite steps towards agriculture and complexity were taken in a global scale. This simple fact cannot be ignored. The varied adaptations and adaptive strategies huntergatherers used to cope with different environments in northern South America since the Late Pleistocene appear to have been followed by a largely-Holocene pattern of diminishing territorial mobility and settling-in processes, linked to the appearance of new technologies, especially for processing previously unused, harder-toget resources. This amounts to saying that resources yielding the lowest return per unit of work were exploited only when stress was placed upon more productive resources (Hayden, 1981). Phrasing it differently, the Late Pleistocene/Early Holocene pattern would be economically characterized by generalized and free-ranging hunting-gathering, while the Holocene pattern would be a more territorially restricted and, therefore, economically specialized hunting-gathering economy. The adaptive change would have brought rearrangements in most aspects of cultural systems, notably in the economy and its material correlate, technology. Changes in mobility and technology, however, must be qualified. The use of mobility as an indicator must be approached from a local or regional point of view, because in a wider perspective it may only reflect economic orientation and not adaptive changes (see Meltzer and Smith, 1986: 15; Willig and Aikens, 1988: 29). The appearance of new technologies as a characteristic of the post-glacial (see Hayden, 1981) must not be exclusively restricted to grinding tools, relatively common in South America only after 8000 BP. Other technologies, perhaps not as visible and widely recognized (such as indirect

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cooking for leaching otherwise poisonous food stuffs), should also be considered. Although the equation between technological and adaptive change is one of the cornerstones of archaeological analysis, it is unsafe to attach the uncontextualized appearance in the record of a given technology freely to a concomitant adaptive change. In other words, adaptive change can be seen only through the eyes of technology in regional sequences. Otherwise we run the risk of misinterpreting isolated records. Grinding artifacts are one of the best examples. American archaeologists have tended to equate grinding tools with the adaptive changes of the post-glacial, because it has been assumed that those artifacts are always tied to the exploitation of previously unused plant resources. That procedure, however, is apparent only in regional sequences in which grinding tools appear only after other technologies were used. But it is also possible, that grinding tools were used as part of the tool kit in the initial colonization of certain ecosystems, perhaps even since Late Pleistocene times. In this case, grinding tools cannot be taken as representing the kind of adaptive changes that happened since the Early Holocene. In South America, grinding stones and wooden mortars may occur widely in Late Pleistocene contexts, as the evidence from Monte Verde indicates (Dillehay, 1989: 15-16). Edge-ground cobbles were found in Chobshi (Lynch and Pollock, 1980: 33) in Ecuador, the deposits of which have a 10,000 BP date, but their exact provenience and age are unknown. Engel (1970: 56) claims to have found grinding stones in all levels of Quiqch6 and Tres Ventanas, two caves situated above 3000 meters in the upper Chilca valley in Peril. If that is the case, grinding stones found in the oldest level of Tres Ventanas would be dated to ca. 10,000 BP. However, it is impossible to assess his claim based on the brief report published so far (cf. Cohen, 1977: 241). The dates between 10,000 and 9000 BP associated with grinding stones in San Isidro (Gnecco, 1994), in the valley of Popayfin, in Colombia; Araracuara, in the Colombian Amazon (Cavelier et al., 1995); and Provincial, on the Orinoco river in Venezuela (Barse, 1990: 1389), may simply indicate that the technology used by hunter-gatherers to adapt to tropical forests included such tools from the beginning. However, they may represent adaptive changes, such as the processing of resources previously neglected. If that is the case, we could speculate that the consequences of resource stress were felt earlier in tropical forests, where high mobility, low population densities, and large territories are necessary conditions for hunter-gatherer adaptations? Again, these two possibilities can be assessed only in regional sequences. 1 This general statement must be qualified, however. Unusual situations of resource concentration may also occur in the tropics, allowing the existence of larger, less mobile groups. This seems to be the case, for instance, with the evidence uncovered in Caverna da Pedra Pintada in the Brazilian Amazon (Roosevelt et al., 1996).

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The evidence from the Sabana de Bogot/~ suggests that mobility decreased at the onset of the Holocene, leading to adaptive strategies centered on exploitation of the fauna and flora of the andean forest/pfiramo ecotone. This pattern may have persisted, with minor changes, for at least 3000 years (Correal and Van der Hammen, 1977: Van der Hammen and Correal, 1978). Technological shifts, as suggested by the first indications of the domestication of Cavia porcellus and the manufacture of edgeground cobbles, traditionally associated with root and seed processing (Ranere, 1980: 339; see Ranere, 1978), do not occur before 6000-5000 BP (Van der Hammen and Correat, 1978: 169). Increasing stylistic diversity in the diachronic dimension can be helpful in monitoring decreased mobility and settling-in processes. The rationale behind this argument is that stress over resources and the far-flung processes this set in motion could have resulted in some areas in subsistence instability and/or economic competition between social groups. If those groups were previously bound by a diversity of interaction mechanisms, competition either could have severed that binding (Hayden, 1981), or could have maintained it or even enhanced it (Hodder, 1982): Whatever the outcome increased cultural fractionation resulted, with consequent increased stylistic differentiation. Practically speaking, increased stylistic diversity can be assessed diachronically through a pattern of decreased areal extension of archaeological horizons. Price (1991: 200) notes that there are several changes in lithic projectile points in Europe at the Pleistocene/Holocene frontier, the most salient of which is the fact that their geographical distribution decreases and the number of zones with distinctive types increases with time. The same pattern has been documented for North America, where after 10,800 BP there is a dramatic increase in regional types, in contrast to the nearly pan-continental Clovis type (Tankersley, 1989: 39, 1990:286 288; Anderson, 1990: 189). Although the preceramic data for northern South America are not as finely grained as that for Europe or North America, it is still possible to see a trend towards regionalization, and perhaps decreased mobility, in the distribution of projectile point types the further we get into the Holocene. Whereas the fishtail horizon is widely distributed from Tierra del Fuego to Venezuela, and, perhaps, northern Colombia, the subsequent, widely diversified horizons are much more restricted, both in time and in space. In sum, the archaeological data from northern South America plainly rules out the old dichotomy specialists/ generalists linked to the Pleistocene/Holocene boundary. But there are post-glacial patterns, such as decreased mobility and technological innovations, that must be explained if we are to understand the eventual abandonment of hunting-gathering in most areas. Although that explanation must necessarily take place against the envir-

onmental background of the Pleistocene/Holocene boundary, what is at stake is the question if that boundary really had an important bearing in the ultimate course cultural evolution took in northern South America. 1.2. The environment Paleoenvironmental reconstructions for northern South America have decisively contributed to our understanding of Pleistocene and Holocene climatic variations which affected the composition of most ecosystems. In some areas, such as the eastern highlands of Colombia, the resolution of post-glacial climatic changes is rather impressive (e.g. Van der Hammen and Gonzfiles, 1960; Van der Hammen, 1961, 1981; Van der Hammen and Vogel, 1966). A general observation that has emerged as research accumulates is the view that Pleistocene and post-glacial climatic events played a major role in the evolution of the biomes of the southern hemisphere, displacing the previously held conviction that this area remained relatively stable during the Quaternary (Simpson-Vuilleumier, 1971: 778; Van der Hammen, 1974). Although it seems undisputable that the post-glacial climatic oscillations caused major shifts in resource densities and distributions in most if not all ecosystems, resulting in some areas in environmental instability and unpredictability during the Early Holocene (Piperno, 1994: 638), this kind of shift cannot be exclusively associated with the Pleistocene/Holocene boundary. Such shifts happened many times before, some with even more intensity. Therefore, it seems highly plausible that nonenvironmental variables interacted against the changing environmental background of the Pleistocene/Holocene boundary to unfold the Holocene events. In this perspective, the Pleistocene/Holocene boundary was just a background, an important one admittedly, but not the main cause responsible for those events.

2. Discussion

The relevance of the climatic shifts of the Pleistocene/ Holocene boundary for the understanding of the events that lead to the dimissal of hunting-gathering in favor of agriculture and village life is under careful revision all over the world. While climatic change was until a decade ago the preferred prime mover in America and Europe for explaining world-wide Holocene events, its heyday has come to an end or, at least, to a pause. Curiously, however, while in most areas the longpresumed leading role of climatic shifts in cultural change is being challenged and downplayed, in Australia and neighboring islands, where cultural stability for over 40,000 years led investigators to consider the effects of climatic change on culture as negligible, there is

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a growing recognition of its importance (e.g., Hope and Golson, 1995; Porch and Allen, 1995; but see an opposite view in Gosden, 1995). These two positions are less antithetical than they appear, however. Both sprung from the fact that single causes of cultural change were rejected in anthropology years ago, entering a long period of darkness. That is the case for population pressure: in Europe and America, and climatic change elsewhere. While favoring one variable over other is clearly a function of paradigmatic views and research traditions (not to say intellectual fashion), which normally produce tremendous biases, the fact is that we badly need a better understanding of cultural change and continuity with regards to the Pleistocene/Holocene boundary. It is my contention that the data from northern South America forces us to downplay the role of climatic change and to consider other causes. This does not mean, however, that climatic change did not affect most ecosystems, simply that its effect over culture was not as dramatic as has been suggested. The archaeological record from northern South America on the Pleistocene/Holocene boundary shows a remarkable variety of adaptations to markedly different ecosystems. Among the ecosystems occupied and exploited were different kinds of tropical forests. The early South American adaptations to tropical forests alone rules out the possibility that those hunter-gatherers were specialized hunters, simply because animal biomass in tropical forests is scant - - except for fish in some areas and a successful non-agricultural adaptation to those environments ought to be based on high mobility and the use of a wide variety of resources, especially plants. Therefore, this evidence alone invalidates the widely held specialists-generalists dichotomy supposedly falling at the Pleistocene/Holocene boundary. Although the Pleistocene/Holocene transition certainly affected the composition of most ecosystems, the gradual extinction of megafauna did not affect most groups of huntergatherers simply because they did not rely on big mammals for survival. Post-glacial ecosystemic rearrangements certainly had an impact on human populations, but it is dubious that the impact had the same consequences over the entire continent. Accepting that hunter-gatherers occupied a diversity of environments in northern South America since the Late Pleistocene also implies that the dramatic climatic changes associated with the end of the Last Glacial were felt in differential ways that still await a more detailed investigation. We can be categorical, however, about one crucial fact: those climatic changes certainly affected the -

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2 Population pressure is to be distinguished from population growth and population density; the key difference is the relationship with the resource base. Keeley (1988: 373) defined it as "the ratio between human population density and resources".

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animal and botanical composition of the ecosystems of northern South America but did not provoke a change that forced an economic shift between specialized hunting and generalized gathering, simply because specialized hunting in those environments may not ever have been possible. Adaptive changes must have necessarily occurred as the composition of the ecosystems changed, but those changes were certainly not the drastic dichotomy implied in the specialists/generalists transition. Further, the climatic changes of the post-glacial cannot alone account for the gradual evolution from hunting-gathering to agriculture in northern South America. The conclusion is inescapable: the Pleistocene/Holocene frontier means little if examined in the light of the archaeological evidence (see Gosden, 1995: 816, for the same conclusion regarding Greater Australia). It is no more than a chronological reference, a time period coincident with social trends ultimately culminating in agriculture and complexity; but the boundary cannot be linked directly, in environmental terms, to the unfolding of the events that followed the gradual, Holocene pan-continental demise of hunting-gathering. This discussion cannot be of just regional interest. What is finally at stake, in terms of general theory, is the explanation of cultural change. If we are to keep explaining the-largely-Holocene events leading to agriculture, settled life and social complexity in terms of cultural responses to the climatic changes happening around the Pleistocene/Holocene boundary, then there must be a clear, global correlation between behavioral and environmental change. If there is not, or if we can demonstrate that behavioral changes had a different timing, then the whole argument must be abandoned. I am afraid that is the case, and that this paper is just another counterexample to the argument. Therefore, in explaining those events we have to look hard for the interrelationship of several variables, downplaying the leading role climatic oscillations have had. In this line of reasoning, I think that long-time ostracized variables, such as population pressure, will be considered again more carefully (but see Bender, 1978; Drennan, 1987, for critiques of this variable), along with newly-favored social variables - - which Gould (1985) called "transformational" as opposed to "adaptational" variables - - such as sectional competition for prestige. Although arguments for the control, both cultural and natural, of population growth among hunter-gatherers (e.g. Sussman, 1972; Cowgill, 1975) still haunts the discipline, it is an undeniable fact that world population grew continuously in the pre-agricultural, pre-settled past, as Butzer (1991: 144-145) has shown so convincingly. Moreover, the result of Keeley's (1988) careful research on ethnographically-known huntergatherers cannot be ignored: "Whatever the cause of socioeconomic complexity in hunter-gatherers, demographic pressure on resources must be considered a crucial component of any causal model. To ignore or dismiss

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the role of demographic pressure means not only ignoring the empirical correlations determined here but also the simple, and therefore robust hypotheses that argue that complexity and demography must be related" {Keeley 1988:396 397t. In sum, in considering the human side of the Pleistocene/Holocene boundary the main problem is one of scale: it is crucial to ask whether or not the same global effects (if a w l originated from identical global mechanisms: whether or not the same global mechanism (if anyt produced identical effects: whether or not human local responses to Pleistocene/Holocene climatic change {if a w l can be observed in other regions. While the resolution of these questions may take years and. hopefully, strong paradigmatic consensus, our current knowledge of the situation allows us to state with confidence that the unfolding of the Holocene events leading to agriculture and complexity may have had different causes world over. Moreover, the timing of those events seems to be markedly different from zone to zone, and it hardly coincides with the Pleistocene/Holocene boundary. This conclusion, if supported, can have dramatic consequences for our understanding of cultural phenomena and for the way we perceive the operation of culture.

Acknowledgements Some of the arguments developed in this paper were discussed at length in nay dissertation for Washington University. ! thank the members of my committee for their patience and advice, especially Dave Browman and Pat Watson. The comments of the two reviewers, Nora Flegenheimer and Ruth Gruhn, helped to clarify some of the issues I have chosen to deal with. Although editors normally decline the honor, I thank Marcelo Zitrate for his editorial skills and care, which have produced a much better paper, and for the invitation to participate in this issue.

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