History is a huge topic, at least in the ways that I've concieved of it. History potentially encompasses any change over time, whether reckoned by historical documents, oral history, or paleontological data. Having staked out such a broad domain, I nonetheless differentiate history from evolution, primarily to emphasize the taxonomic and genetic aspects of the latter topic (see Evolution for coverage of all this). Here, I cover the last 80,000 years, starting with how and when grizzlies arrived in North America (Early prehistory) and ending with the European-driven extirpations of the last 200 years (see Extirpations). The Holocene falls in between, beginning roughly 11,000 years ago. Given my particular interest in Yellowstone's grizzly bears, I provide a more detailed look at changes that happened during the last 15,000 years or so under a section titled Yellowstone paleoecology. You can find links to each of these subtopics either in the text, here, or in the buttons immediately to the right.
Late Pleistocene to Early Holocene
I chunked everything that might have happened between 80,000 and 11,000 years ago under the billing of "Early prehistory." This period encompasses the last act of the last ice age (or the Last Glacial Maximum or LGM) as well as upheavals of the transition from that icy epoch to the much warmer Holocene. When grizzlies first arrived at mid-latitudes of North America from Asia (via Beringia) around 80 to 55 thousand years ago, thanks to a relatively short-lived passage through the northern continental icesheets, they encountered an incredibly rich beastiary of resident large carnivores. These included lions, dirk-toothed cats, sabre-toothed cats, giant short-faced bears, Florida cave bears, and dire wolves, all of which are illustrated above. Even though food was probably abundant, I speculate that the first wave of colonizing grizzlies did not flourish because of competition--and even predation--from these resident carnviores. With the demise of virtually all large-bodied herbivores at the end of the last ice age, almost all large carnivores followed suit, with most extinct by about 13,000 to 12,000 years ago. As a consequence, the world probably opened up for grizzly bears, which spread into eastern North America and north by way of a newly ice-free corridor along the Rocky Mountain front...where they met other newly arrived grizzlies dispersing south from Alaska. But by roughly 10,000 years ago grizzlies has been pushed back into their core western range, although an anomolous disjunct population persisted in northern Labrador probably as descendents of grizzlies that had followed the retreating ice margins north, only to be isolated in a fringe of tundra along the northern Atlantic Ocean.
The Holocene encompasses everything that happened between roughly 11-12,000 years ago and the present, although some call the current unfolding epoch the Anthropocene, in reference to the dominant effect of humans on the Earth's environment. The Holocene has been much warmer and less variable, climate-wise, than the late Pleistocene, with (until recently) peak warmth and drought occurring during a period roughly 9,000 to 5,000 years ago called the Altithermal. When thinking about the Holocene, much of my focus has been on explaining the anomalies of grizzly bear distribution in North America that reveal much about the ecology and environments of millennia past. More to the point, why didn't grizzlies occupy eastern deciduous and boreal forests, at least in any numbers for any length of time? By contrast, Eurasian brown bears (the same species as grizzlies) are (or were) abundant and widespread in the deciduous forests of Europe and throughout the boreal forests of Asia.
I hypothesize that the distribution of grizzlies in North America was curtailed by the combined and synergistic effects of problematic physical environments, competition with resident American black bears, and competition with and predation by burgeoning numbers of humans--First Peoples. Boreal forests in North America are less rich than those of Asia because our forests lack the fat-rich seeds of stone pines, which are abundant in northern Asia. Moreover, Asian boreal forests lack black bears, unlike in North America where grizzlies competed with black bears (and humans) for shared foods, but at a severe competitive disadvantage especially when it comes to a scramble for the richest patches. Because of their smaller size, smaller home ranges, and higher reproductive potential, black bears can exist at much higher densities than grizzlies. They can also more efficiently use less rich foods and food patches. Add some mortality meted out by people hunting bears for meat, and the balance was and is very likely definitively tipped against grizzlies in boreal forests.
Farther south, the Great Plains very likely posed their own problems for grizzlies. Rich foraging environments on these grassland spanning the mid-continent north to south are concentrated along rivers that run west to east. Competition and other problematic interactions with humans and black bears were probably heightened by this funneling effect, very likely, again to the detriment of grizzlies moving east. The only food that grizzlies probably dominated was carrion from bison--because humans were disinterested, and because grizzlies could physically displace black bears. As a result, I speculate that the fate of grizzlies on the Great Plains, which included potential colonizers of the deciduous forests farther east, hinged about the distribution and abundance of bison. Given that bison populations waxed and waned with wet and dry periods and with the progressive spread of less-nutritious C4 grasses from south to north, it is easy to imagine grizzly bear populations waxing and waning in synchrony. In fact, there is evidence that grizzlies may have been entirely absent from most of the Great Plains during periods of peak drought.
Taken together, these various lines of evidence suggest that North American grizzly bears were being affected by people for millennia prior to the arrival of Europeans. Resident black bears were likely having their effect as well, at odds with blithe assumptions on the part of most people that grizzlies are at the top of the ursid heap. And bison, which we now find with grizzlies only in and near Yellowstone Park, were in the past, unlike the present, a critically important food for grizzly bears in a significant part of their continental range. I elaborate on all of these theses in sections related to each titled The human factor, The black bear factor, and The bison factor.
The concluding chapter of grizzly bear history on this continent is dominated by the mass extirpations that occurred between roughly 1800 and 1970. During this period, grizzlies in the continguous United States were exterminated from 95-98% of their former range, leaving populations of any size only in the areas where we currently have them--in the Yellowstone and Northern Continental Divide regions of Wyoming, Montana, and Idaho. Smaller populations hung on in the Cabinet-Yaak and nearby Selkirk Mountains of northwestern Montana and adjacent far northern Idaho, along with a few bears in the North Cascades of Washington and the San Juan Mountains of southern Colorado. The cause of these extirpations is straight-forward: the arrival of well-armed extremely intolerant Europeans intent upon eradicating all large carnivores. Never before had grizzlies faced a predator so lethal and so malicious. I cover this sordid history in more detail under Extirpations along with an exposition on the still relevant concept and elements of human lethality under The lethality factor.