Passage A
The sudden appearance of diverse, complex animal body plans in the fossil record, commonly known as the Cambrian explosion, represents one of the most significant events in evolutionary history. The prevailing ecological hypothesis suggests that this rapid morphological diversification was catalyzed primarily by the advent of macroscopic predation. Prior to this period, marine ecosystems were dominated by soft-bodied organisms grazing on microbial mats. The evolution of active predators, equipped with specialized feeding appendages and sensory organs, introduced unprecedented selective pressures. In response, prey species rapidly developed protective adaptations such as calcified exoskeletons, spines, and sophisticated defensive behaviors. This intense biological "arms race" between predators and prey fueled a self-propagating cycle of morphological innovation. The fossilized remains of Anomalocaris, a formidable apex predator, alongside heavily armored trilobites, perfectly encapsulate this dynamic. As predators evolved better ways to capture prey, prey evolved better ways to escape, driving the explosive radiation of anatomically complex taxa. In this view, the engine of the Cambrian explosion was inherently ecological: it was the complex web of new trophic interactions that forced life forms to innovate or perish, thereby sculpting the diverse body plans we recognize today.
Passage B
While the ecological changes characterizing the Cambrian period were undoubtedly profound, attributing the Cambrian explosion solely to a predator-prey "arms race" conflates the survival of new forms with their origin. Ecological pressures can only select from the anatomical variations that are already genetically available. Therefore, the true catalyst for this rapid diversification must be sought at the genomic level. Recent advances in evolutionary developmental biology point to the expansion and duplication of regulatory gene networks, such as Hox genes, as the primary drivers of Cambrian morphological diversity. These genetic regulatory toolkits dictated the body patterning of embryos, establishing the anterior-posterior axis and segment identity. Mutations within these networks could trigger massive, cascading changes in phenotype with relatively minor genetic tweaks. A sudden increase in the complexity of these genetic networks provided organisms with the architectural flexibility to develop novel appendages, specialized segments, and varied body plans. Without this intrinsic developmental plasticity, no amount of external ecological pressure could have conjured such a vast array of complex anatomies. Thus, genetic innovation was the prerequisite foundation; ecological interactions merely served as the sieve through which these newly minted, genetically facilitated variations were subsequently sorted.
Which of the following best describes how the author of Passage B would most likely respond to the assertion in Passage A that the biological arms race "fueled a self-propagating cycle of morphological innovation"?
- They would qualify the assertion by noting that such an ecological cycle could not generate novel anatomical structures without pre-existing genomic plasticity.Cevap
- BThey would completely dismiss the assertion, arguing that ecological interactions such as predation had absolutely no influence on the anatomical features of Cambrian organisms.
- CThey would counter the assertion by arguing that the arms race merely served as a sieve, making ecological pressure the true prerequisite foundation for diversity.
- DThey would agree with the assertion, provided that the cycle of morphological innovation is understood to have generated the rapid expansion of regulatory gene networks.
- EThey would point out that the assertion is flawed because active predators could not have existed during the Cambrian period without the prior morphological diversification of prey.