Question

Read the following passage carefully.

For decades, the "overkill" hypothesis has served as the dominant explanatory framework for the rapid extinction of large mammals—megafauna—at the end of the Pleistocene epoch. Proponents of this theory point to the seemingly damning timing of human migration patterns into the Americas and Australia, which closely aligns with the abrupt disappearance of dozens of large species in the fossil record. According to this model, early human populations, armed with advanced projectile technology and hunting cooperatively, rapidly decimated naive animal populations that had evolved without a comparable apex predator. This hypothesis gained significant traction because it offered a single, elegant mechanism to explain extinctions across vastly different geographical landscapes.

However, recent high-resolution climatological data complicates this straightforward narrative. During the exact same period, the Earth underwent extraordinarily violent climatic shifts, transitioning rapidly from the Last Glacial Maximum to the warmer, wetter Holocene. This rapid environmental upheaval drastically altered global flora, replacing the highly nutritious, diverse steppe-tundra vegetation that many megafauna relied upon with less nutritious, homogeneous tundra and dense forest biomes. For animals with massive caloric requirements, this sudden habitat fragmentation would have severely reduced carrying capacities and isolated breeding populations, leaving them deeply vulnerable to any additional ecological pressures. The loss of keystone herbivores may have also triggered further cascading ecological collapses.

Yet, the pure climate change hypothesis also suffers from significant evidential shortcomings. As several paleontologists have correctly noted, Pleistocene megafauna had survived numerous previous, equally severe glacial-interglacial climate fluctuations without suffering mass extinction. If climate alone were the driver, these species should have vanished hundreds of thousands of years earlier. Conversely, the human hunting model fails to account for the simultaneous extinction of several species that were almost certainly never hunted by humans, as well as the paradox that some heavily hunted species, such as bison, survived and even thrived. Furthermore, detailed fossil analysis indicates that the decline of some megafaunal populations actually began before humans arrived on their respective continents, further undermining the idea that overhunting was the sole initial trigger.

To resolve these paradoxes, paleontologists have recently begun cross-referencing archaeological kill sites with regional paleoclimate reconstructions. In regions where human arrival coincided with periods of relative climatic stability, megafaunal populations often persisted for millennia alongside early hunters. Similarly, in geographic pockets that experienced severe ecological shifts but remained unpopulated by humans, megafauna generally adapted by shifting their ranges. It is only in the stratigraphic layers where extreme and rapid vegetation turnover perfectly aligns with the initial appearance of human hunting tools that the abrupt, widespread collapse of megafaunal populations is consistently observed. By mapping these two distinct variables onto the same timeline, researchers are finally moving past the restrictive binary debate that has historically dominated the field of paleontology.

Which one of the following most accurately expresses the main idea of the passage?