Question

The following dual passages discuss theories regarding the extinction of Pleistocene megafauna.

Passage A
The debate over the extinction of megafauna at the end of the Pleistocene epoch has long been dominated by two competing theories: human overkill and climate change. Proponents of the overkill hypothesis argue that the rapid geographic expansion of anatomically modern humans into the Americas and Australia brought a novel, highly efficient predator into vulnerable ecosystems. In these regions, large mammals had evolved in the absence of hominins and consequently lacked appropriate anti-predator defensive behaviors. The archaeological chronology of these extinctions strongly supports this anthropogenic view; the sudden disappearance of massive species like the mastodon, the dire wolf, and the giant ground sloth maps remarkably well onto the timeline of initial human colonization across these landmasses.

Critics of this hypothesis frequently point to concurrent climatic shifts, arguing that the profound global warming marking the end of the Last Glacial Maximum devastated megafaunal habitats. It is undoubtedly true that this transitional period saw significant alterations in global vegetation patterns, which forced large herbivores to adjust their foraging strategies and migration routes. However, the fossil record demonstrates that these same animal lineages had successfully navigated dozens of virtually identical glacial-interglacial climate transitions over the preceding two million years. The climatic warming at the end of the Pleistocene was not uniquely severe in the geological record. Therefore, while fluctuating climates certainly altered the spatial distribution of certain species, it was the unprecedented pressure of human hunting that ultimately drove these otherwise remarkably resilient populations to extinction. The introduction of human hunters was the sole decisive variable.

Passage B
For decades, the so-called "blitzkrieg" model of Pleistocene extinctions has captured the popular and scientific imagination, positing that waves of early human hunters single-handedly eradicated dozens of megafaunal genera in a geological instant. Yet this human-centric narrative profoundly underestimates the sheer severity of the ecological restructuring that occurred at the Pleistocene-Holocene transition. The conclusion of the Last Glacial Maximum initiated a period of rapid, extreme warming that fundamentally dismantled the "mammoth steppe" and other highly productive, mosaic ecosystems across the globe. These intricate, nutrient-rich plant communities were rapidly replaced by starkly homogenous, lower-quality biomes—such as expansive boreal forests and tundra—that simply could not sustain the immense caloric and diverse nutritional requirements of massive herbivores.

As their optimal habitats shrank and became increasingly fragmented, megafaunal populations inevitably suffered severe nutritional stress. This ecological bottleneck led to collapsed birth rates, genetic isolation, and heightened vulnerability to disease. It is exclusively within this context of profound, systemic ecological decay that human impacts must be evaluated. Archaeological evidence undeniably confirms that early humans occasionally hunted megafauna, and it is entirely plausible that this targeted predation served as the coup de grâce, accelerating the demise of certain severely compromised herds. However, characterizing human hunting as the primary driver of extinction ignores the underlying reality that these species were already in a state of terminal decline. Humans were not the architects of the megafaunal collapse, but merely opportunistic actors within a much broader ecological catastrophe driven entirely by a shifting climate.

Which one of the following expresses a claim about the end of the Pleistocene epoch that is explicitly or implicitly endorsed by the authors of both passages?