The human factor: 15,000-200 years ago
My thesis here is that humans have been affecting grizzly bears in North America for millennia--long before the arrival of Europeans. I am particularly interested in explaining the Holocene distribution of grizzly bears which, for reasons that I articulate under The Holocene, is actually quite strange--or at least at odds with where I would expect grizzly bears to have lived on this continent before the slaughter by newly-arrived Europeans that started roughly 200+ years ago (see Extirpations). To develop a defensible explanation I found that I needed to consider the inter-related facets of diet, predation, and competition, which invoked three main actors: people, black bears, and bison. My focus here is on the human factor. I cover the black bear and bison factors more explicitly in other sections devoted to these species and their effects on grizzly bears.
So...turning to the human factor. There has been a huge amount of ink and academic blood shed over arguments about when humans first arrived in North America. Much of the debate has been fueled by disagreements over the extent to which humans were a factor in driving the extinction of virtually all of the large-bodied mammals at the end of the last Ice Age. With the exception of a very few species, this window of extinction was fairly narrow, roughly between 13,500 and 12,500 years ago.
Debate over the human role still rages, closely intertwined with arguments over when humans first arrived in the mid-continent of North America. Some argue that humans could have arrived 40-30k years ago (40,000-30,000 years ago), possibly across the Atlantic from the east carrying a European stone technology called "Solutrean." At the risk of bringing the wrath of proponents down on me, I find evidence for this hypothesis to be meager at best, and contradicted most eloquently by the genetic relatedness of First Peoples to natives of Siberia. Another hypothesis posits an equally early arrival, but in this case by Siberian emigrants following ice-free coastal areas from Beringia (much like what is posited for grizzly bears), potentially all the way to South America. A role for boats is invoked in this scenario. Still others hold to a late arrival, roughly 13k years ago, primarily by people moving down from Beringia along a newly-opened ice-free corridor along the Rock Mountain front in modern-day Alberta--again, much like what has been hypothesized by some for grizzly bears. This late arrival fits with many of the dates for emergence of a stone technology called "Clovis," which has been closely identified with the hunting of large mammals. As result, the exact timing and geospatial spread of this technology have also been hotly debated. Finally, there is a synthetic hypothesis, which I find to be the most compelling, positing three waves of emigrants, encompassing all of the scenarios described above (with the defensible exception of early European origins). Your conclusions regarding the role of humans in megafaunal extinctions largely hinge on which hypothesis you adopt.
However, my argument here does not depend upon adopting any one of these hypotheses about when and how humans arrived. It matters little to my view of early human-grizzly bear relations whether humans arrived 40k or 12k years ago, or the exact role that humans played in megafaunal extinctions. The fact is that almost all large-bodied mammals went extinct in a relatively short period of time at the same approximate time that evidence of human occupation burgeoned along with the widespread and relatively rapid emergence of advanced lithic weaponry (Clovis followed by Folsom technology). In any case, coming down definitively on the side of one hypothesis or another entails the risk of being figuratively eviscerated by any number of academics for whom there appear to be fairly substantial ego stakes.
So...what were the implications of these changes for grizzly bears? First, like humans, grizzlies probably did not fare well during the periods of hot-dry climate (see The Holocene). These were times of diminished food for all omnivores. Second, to the extent that humans were competitors with and predators on grizzlies, the dramatic increase in human numbers about 2,000 years ago probably did not benefit grizzly bears. Add to this the predictable and simultaneous increase in human lethality that came with use of the bow and arrow, and the negative consequences for grizzlies could have been significant. We have no way of knowing whether grizzly bear populations (and distributions) declined substantially during the several millennia prior to arrival to Europeans, but it seems likely--and is the most consistent with the facts of any scenario that I can readily imagine.
The gist of my thesis
I posit that the First Peoples (which I use to include Indians, First Nations, Native Americans, and Puebloans) competed with grizzly bears for most foods and also killed grizzlies in varying numbers depending on regional culture and environment. I speculate that this competition with and predation on grizzly bears by humans interacted with competition for food by black bears and the configuration of major North American vegetation zones to confine grizzlies (or at least most of them) to western parts of the continent, especially after 10,000 years ago. The motivating question is straight-forward: basically, why did grizzly bears not occur (at least in any numbers) east of the Great Plains or farther east in the boreal forests of the North? I consider my thesis to be compatible with a deep spiritual connection and high level of respect for grizzlies among First Peoples. That aside, my basic premise is that people and bears were both driven by the need to survive and even thrive, and that this fundamental dynamic played out in varying physical and biological contexts that entailed specific demands as well as opportunities for each of these players.
Regardless of whether or not you believe that humans inhabited North America south of the continental ice sheets during the Last Glacial Maximum (LGM), the fact remains that reliable evidence of this occupancy is scant. If nothing else, this thinness of evidence suggests that humans were not numerous, especially in the harsh regions just south of the ice sheets that I speculate were enclaves of Late Pleistocene grizzlies (see Early prehistory). In other words, even if people were around, I doubt that they were interacting with or having much of an effect on grizzlies during the LGM. But that probably changed after 15-13k, when humans clearly increased in numbers and deployed particularly lethal stone-tipped spears that were very likely powered by atlatls (spear-throwers).
With that in mind, it's interesting to look at the map to the left. The white dots denote the remains of grizzly bears found by archeologists and dated to between 10,000 and 200 years ago. The red line denotes the approximate distribution of grizzly bears around 1700-1800 A.D. The striking correlation of the early historical range with the distribution of archeological finds suggests that grizzlies have occupied much the same range since 10k years ago (I address the Utz site and provide more detail on the historical range in the Holocene).
The early Holocene
Of particular relevance here, the varying shades of purple in this map denote the relative densities of fluted spear points (of the Clovis and Folsom technologies) found so far by archeologists. The map was put together by the Canadian paleontologists John Ives and colleagues. Densities of spearpoints have been used as a rough proxy for human population densities, realizing that density of finds could also be affected by regional variation in the numbers of people looking for or stumbling across spearpoints, as well as by differences in aridity along with resulting differencies in the extent of ground exposure.
What does this pattern of human artifacts suggest? Foremost, that, compared to the West, humans were more numerous in what is now the eastern United States as early as 10-9k years ago. There are subsidiary enclaves of stone-point abundance in the Great Basin and desert Southwest, both of which could be an artifact of the aridity of these environments (see my point immediately above). That aside, it is interesting to note the extent to which the archeological remains and reconstructed historical range of grizzly bears do not overlap with the areas of greatest apparent human densities. It is also noteworthy that the area where human artifacts are uniformly most dense and where there is the greatest dearth of evidence for occupancy by grizzlies (i.e., the East) is also where forest cover had spread most quickly and was densest by 12-9k years ago (see Early prehistory), presumably to the advantage of black bears (see the Black bear factor).
So...these pattern suggest that humans could have had an affect on where grizzly bears lived as early as the beginning of Holocene, many thousands of years ago. This would fit my thesis that grizzlies had a relatively fleeting moment in the East, roughly between 15k and 10k, when the habitat there was still less densely forested and recently deglaciated areas remained open (see Early prehistory).
Protohistorical and early historical times
This brings me to early (written) historical times and the slightly earlier period encompassed by reliable cultural memory--roughly 500 and 200 years ago. The maps to the right are relevant to this period, specifically bear-related cultural traditions (panel A) and physical densities and agricultural traditions (panel B) of First Peoples. A key distinction is between groups that cultivated corn (and other domesticated plants) and those that did not. And here I need to acknowledge that the information depicted in these maps draws on the compendious efforts of numerous ethographers, historians, and anthropogists.
There is no doubt that First Peoples could and did kill grizzly bears. But, to what extent and for what reasons? I drew heavily on Irving Hallowell's seminal monograph on bear ceremonialism (as well as other works) to put together the map of different bear-related cultural traditions in Panel A, each denoted by a different color. You can also see the mid- to late-Holocene distribution of grizzlies (as a beige overlay).
Burgundy denotes an active hunting tradition, where native peoples sought out bears for their meat, typically while bears were in their winter dens. Most hunting targeted black bears, but some targeted grizzlies as well. It is perhaps not a coincidence that pursuit of bears for meat occurred in a region (the boreal forest) where there was comparatively less meat biomass compared to coastal and plains areas. In short, this boreal region is where one might reasonably suspect that pre-European humans were most lethal to grizzly bears.
The orange denotes areas where people apparently killed grizzlies primarily in defense of their lives, homes, food, and (more recently) horses, or as part of activities associated with spiritual practices. In other words, throughout most of this region people did not actively seek out grizzlies to kill them for food which, not surprisingly, coincided with the availability of ample meat from other sources--bison, deer, and pronghorn on the Great Plains and spawning salmon along the Pacific coast. Parenthetically, the limited yellowish area denotes a tradition typified by active avoidance of grizzlies, notably in coastal and nearby inland parts of modern-day California where grizzly bears were known to be both abundant...and large.
The map in Panel B shows estimated relative densities of First Americans, along with whether or not corn cultivation was part of their agricultural economy. Much of this information was compiled by Harold Driver and Douglas Ubelaker. Corn cultivation is a rough proxy for how settled or sedentary a group might be. First Peoples were probably most numerous along the Pacific coast, in the Mexican highlands, and in places along the Atlantic coast. By contrast, there is little doubt that, barring the Southwest, human densities were lowest in interior western regions. Of further note, First Peoples practiced corn cultivation--and thus tended to be more sedentary--east of the approximate middle of the Great Plains and south of the boreal forests.
What is to be surmised from this information? For one, it looks like grizzlies were able to persist where First Peoples were least numerous and where they did not often kill grizzly bears--and, if so, primarily in defense of life and property or for ceremonial or other spiritual reasons. The circumstances associated with corn cultivation by First Peoples appeared to be problematic for grizzlies, especially at the eastern edge of their range (see immediately below). People who engaged in corn cultivation in this area tended to settle in permanent villages along rivers. These river bottoms very likely contained the richest habitat for grizzlies. Put another way, the western margin of corn cultivation tended to concentrate people, spatially and temporally, in precisely the same habitats that were probably most actively sought out by grizzlies. Which would predictably increase the levels of both contact and conflict between bears and people, with a predictably bad outcome for the bears. Having said all of this, the effect of corn culture is hard to disentangle from the potential effect of black bears given that corn cultivation coincided almost exactly with where black bear densities were probably the highest (see the Black bear factor).
The final and perhaps most important point is that grizzlies were apparently not able to persist in nor encroach upon the boreal forests--which is probably where, per capita, people were the most lethal to bears. Again, having featured the human factor, the inhospitality of the boreal forests is entangled with the fact that American black bears do much better in these environments compared to grizzlies (see the Black bear factor) and that boreal forests in North America are missing a rich food resource that is abundant in the boreal forests of Asia--the seeds of stone pines (see The Holocene). In addition, Asiatic boreal forests do not support any bears other than brown bears; Asiatic black bears are restricted to Southeast Asia, which has left all of northern Asia free of competition, at least from another ursid. It is reflective of these differences that brown bears are common (if not abundant) throughout the boreal forests of Eurasia, but largely absent from the boreal forests of North America. So...how to put the human factor in context? My speculation is that the main factor limiting grizzlies in our boreal forests is competition for food with black bears, accentuated by the lack of stone pine seeds, which grizzly bears will readily consume (see Whitebark pine). Human-caused mortality may have simply tipped the balance against grizzlies in an already tough situation.
Changes over time
So, let's assume for the sake of the thesis presented here that people affected the distribution of grizzly bears as early as 10 millenia ago. This, then, begs the question: What was happening over time with the numbers and distributions of First Peoples, especially prior to the arrival of Europeans? Perhaps needless to say, this is a politically-charged topic of relevance to judging the magnitude of genocide perpetrated by Europeans. Almost certainly there were many more First People prior to arrival of Europeans compared to even one century later. But what about before?
The graph at left summarizes several different estimates or indicators of human population size in North America going back 14,000 years. These estimators derive from things as literal as dated archeological sites, to things as arcane as population sizes estimated from back-casting information from gnomes. The green bars denote numbers of arc sites in Wyoming; the black line, number of arc sites in Yellowstone National Park; and the gray and turquoise lines (bounded by uncertainty intervals), more direct estimates of population size continent-wide. Parenthetically, the orange vertical bars denote periods about which there is consensus regarding the prevalence of hotter often drier conditions (see the Holocene). The wider band farthest left corresponds to what some researchers call the Altithermal, others the Hypsithermal, and others yet, the Holocene Climatic Optimum. Whatever the name, it was a nasty climate for people attempting to make a living in and near the Rocky Mountains.
Related to this last point, the colored horizontal bars at top denote (topmost) different ages used by archeologists to classify their finds, along with epochs or events of particular relevance to explaining population trends (immediately below).
Finally, the inset graph at bottom summarizes information on population declines between 1780 and 1887 for Tribes that lived in or near the Great Plains. This period captures the culminating effects of European settlement on the First People in this area. The gray line is a frequency distribution showing the number of Tribes (vertical axis) as a function of the percent that each was reduced in numbers by famine, disease, and violence (horizontal axis). Notice the number of Tribes that experienced an 80% plus decline. I've also shown the median and range of population losses for village-dwelling (or sedentary) Tribes versus more nomadic Tribes. Losses were most severe among the sedentary Tribes, many of which were located along rivers that served as major transportation and trade routes.
The figure above reveals a remarkable consensus about pre-European population trends, along with some indication of correlates. All of the estimates suggest that numbers of First Peoples reached a pronounced peak sometime during the last 2000 years, pre-dating the arrival of Europeans by about a millennium. Otherwise, three of the four estimates suggest that, prior to then, North America and the Rocky Mountains were sparsely populated. One of the four estimators suggests that there was a spike in human numbers during the Clovis-Folsom period (when big game was abundant), just prior to onset of the hot-dry Altithermal. This estimator also suggests that there was a brief resurgence in numbers after the Altithermal, but, then, a decline with onset of the second of the Holocene's extended hot-dry periods. It is noteworthy that widespread use of pit houses in the northern U.S. Rockies began during the Altithermal. Pit houses consisted of a shallowly-excavated circular floor sheltered by a ribbing of bent poles and over-stretched hides. These abodes are associated with the switch from a diet comprised of mostly bison and pronghorn meat to a diet of greater diversity, reflective of a an impoverished environment and more sedentary lifestyle.
Why the dramatic increase in numbers roughly two millennia ago? Note the introduction of the bow and arrow, which happened surprisingly late in North America. Note, also, the coincidence with the end of sustained hot-dry conditions. Cultivation of corn and other domesticated plants was also spreading during this time. So, there may have been a fortunate coincidence of multiple factors, including conditions that favored agriculture, rebounding game populations, and the spread of new technology (the bow and arrow) that greatly aided hunting. Parenthetically, notice the period denoted at the top for which there is ample evidence of substantially increased inter-Tribal violence. This increase in violence is plausibly related to the burgeoning human population and resulting increased conflict over increasingly scarce resources.
In the section covering prehistorical relations between bison and grizzly bears I make the case that bison were a particularly important food for grizzlies that roamed the Great Plains (see the Bison factor). Such was the case for First Peoples as well. Here I make the case that pursuit of bison by humans may have benefited grizzly bears as well.
The graphics at left summarize information that comes from archeological studies of bison hunting on the Great Plains, with an emphasis on the last thousand years or so. The top map shows the distribution of known mass-kill sites, which actually range from very small (only a few animals) to massive and cumulative over time. This last category typically consists of traditionally-used jumps at which you can find great piles of preserved bison bones accumulated at the base. Probably the most famous of these is the Head-Smashed-In site in Alberta. The different colors denote different types of traps, with arroyo traps being relatively more common to the south, and jumps being more common to the north. Overall, many more traps and jumps have been found in the northern compared to the southern Plains. The inset bars graphs additionally show the percent of all kills that were very small or small, moderate, or large or very large in size, differentiating the northern from central and southern Plains (with the Dakotas included in the central Plains). The overall picture is one of greater exploitation of bison by First Peoples in the north compared to the south, which reflects the fact that bison were consistently more abundant in the more productive northern grasslands. An important note: All of this predates the arrival and use of horses, which allowed for an entirely different style of hunting.
An important additional dimension is the seasonal timing of bison kills by First Peoples. The graph in panel B summarizes all of the information that I've been able to find showing when kills were made, which is largely inferred from the progression of tooth development among younger animals at the kill sites. The pink bars summarize information on Minimum Number of Individuals (MNI) in each kill, summarized for three seasons; the various smooth line behind depict proportions of all documented kills (or assemblages). Each line denotes a different time period or region of the Great Plains. The dominant picture, suggested by both MNI and proportional distributions, is of most mass kills occurring during the fall and winter, which makes sense if you are a hunter who is worried about minimizing meat spoilage as well as laying up supplies for the dearth of winter.
An intersection of the Human factor and the Bison factor
All of this adds up as a potential benefit for scavengers such as grizzly bears. In fact, Chrissina Burke (and Judy Cooper), who between them synthesized much of the information on known bison traps, argued that mass kills constituted "ecocenters" for scavenging carnivores. There is ample evidence that hunters were not able to (or for other reasons chose not to) fully utilize all of the meat from bison that were part of a mass kill. References by archeologists to evidence of "gourmet butchering" are common. Some animals buried at the bottom of a pile were probably not accessible. Some meat might have spoiled before being salvaged. Or there might simply have been an imperative to move on. Whatever the reason, a lot of meat was probably left for scavengers such as bears, especially at larger kills. The exploitation of this meat resource by scavengers has been well-documented through the study of diagnostic tooth marks and other damage to bone. From the perspective of a bear, the timing for delivery of this meat resource couldn't have been better. Fall and early winter are when they put on most of the body fat that will sustain them through the winter fast of hibernation (see Nutrition and Physiology).
A couple of closing notes: The protohistorical distribution of grizzly bears is shown in green on the map in Panel A. It seems more than simple coincidence that the eastern edge of this distribution aligns so closely with the eastern edge of mass kill sites. This correlation may reflect heavy use of--or even dependence on--these sites by bears. Or it might simply reflect the eastern extent of bison abundant enough to sustain bison-oriented subsistence strategies. Either way, bison are heavily implicated as a key resource for grizzlies on the Great Plains (see The bison factor).
Finally, in addition to being a source of food for bears, mass bison kills could also have been a nexus of conflict between grizzlies and people. It is easy to imagine a grizzly descending upon such a site hard on the heels of when the kill was made. If so, it is equally easy to imagine the hunters putting up a fight. The presence of grizzly bear remains at some of these sites may be evidence of a bad outcome for a bear involved in such a confrontation. On the other hand, humans and bears may have learned over time how to navigate around these kill sites in ways that reduced conflicts. Who knows? Perhaps future research focused on this question might shed some light.
The map to the right shows the spatial dimensions of several factors that I speculate determined the eastward limits of grizzly bear distribution at mid-latitudes. The factors are habitat conditions, indicated by whether the grasslands were dominated by tall, mid-, or shortgrasses; the core distribution of bison; the extent of areas with moderate to high densities of people; and the eastward and northward extent of agriculture, denoted by a dashed line. Note that there is a dashed line corresponding with the eastward extent of corn cultivation centered on Central America and the Southwest as well as a dashed line corresponding with the westward extent of cultivation centered on eastern deciduous forests. Known locations of grizzly bears are represented by red dots denoting an observation by a European explorer; white-centered orange dots denoting either archeological finds dated to within the last 200-500 years or early somewhat vague European references dating to the 1700s and very early 1800s; and dark green patches corresponding with the distribution of grizzlies around 1920.
There are a couple of take-home messages from this map. Almost all of the grizzly bear locations on the Great Plains are contained within core bison range. Second to this, there are essentially no grizzly bear locations in tallgrass prairie, barring a few along the prairie margins in the far north. Complementary to this pattern, there are only a couple of bear locations within areas where corn cultivation occurred, despite the fact that grizzlies seem to have ranged in areas typified by moderately-high densities of nomadic peoples. Corn cultivation was often practiced in association with permanent or near-permanent villages and a more sedentary lifestyle, with villages increasingly centered on riparian areas the farther west you went into the Great Plains. These riparian areas (along with woody draws) supported most of the vegetal grizzly bear foods found within this bioregion. So, my guess is that sedentism coupled with corn cultivation (especially in river bottomlands) was especially problematic for grizzlies because it parked people year-round squarely in the habitats that the bears sought, not doubt leading to the kinds of conflicts that resulted in dead bears.