Soru

Passage A
The sudden appearance of diverse, complex animal body plans in the fossil record approximately 540 million years ago, an event famously known as the Cambrian explosion, remains one of evolutionary biology's most rigorously debated puzzles. For decades, a prominent faction of researchers has argued that this seemingly rapid morphological diversification was primarily triggered by a profound abiotic shift: a massive, global increase in atmospheric and oceanic oxygen levels. Before the Cambrian period, the Earth's oceans were largely anoxic, capable of supporting only simple, mostly sessile organisms with distinctly low metabolic demands. As photosynthetic cyanobacteria and early algae steadily pumped oxygen into the environment over millions of years, a critical threshold was eventually crossed. This newfound biochemical abundance fundamentally altered the physiological possibilities for marine life. It allowed for the robust synthesis of collagen, a crucial structural protein essential for building complex tissues and internal structures. Furthermore, higher oxygen concentrations supported the demanding metabolic rates required for active locomotion, larger body sizes, and the development of hard biomineralized skeletons. While the subsequent evolutionary innovations were undoubtedly intricate, the oxygenation hypothesis ultimately posits that this environmental release from physiological constraint was the fundamental, overarching catalyst that made the Cambrian radiation possible.

Passage B
Traditional explanations for the Cambrian explosion often lean heavily on the establishment of permissive environmental preconditions, most notably the gradual accumulation of atmospheric oxygen. However, framing this monumental evolutionary event merely as a passive reaction to improved abiotic conditions fails to adequately account for both the extraordinary speed and the highly specific direction of the morphological changes observed in the fossil record. A more compelling and comprehensive explanation centers on emergent ecological dynamics—specifically, the advent of macroscopic predation. When the first mobile, carnivorous predators evolved, they introduced unprecedented and fierce selective pressures into previously tranquil marine ecosystems. Prey species were suddenly forced to rapidly evolve sophisticated defensive adaptations, such as heavily calcified shells, intricate burrowing behaviors, and enhanced sensory organs, just to survive. Predators, in turn, were driven to evolve specialized gripping appendages, acute compound vision, and greater hydrodynamic speed to overcome these defenses. This dynamic, escalating evolutionary arms race created a powerful feedback loop of intense biotic pressure. Therefore, while sufficient oxygen was undeniably a necessary physiological prerequisite for the existence of large-bodied life, it was the novel, intense ecological interactions between newly evolved predators and their prey that actively drove the explosive evolutionary radiation defining the Cambrian period.

Which of the following most accurately describes the joint primary purpose of the two passages?