For decades, paleontologists characterized the Cambrian explosion, which occurred approximately 540 million years ago, as an unprecedented period of rapid evolutionary innovation. According to this traditional view, nearly all major animal phyla appeared suddenly in the fossil record within a narrow window of a few million years. This abrupt manifestation of complex, multicellular life was often interpreted as the literal dawn of animal evolution, a rapid radiation event driven by ecological triggers such as increased atmospheric oxygen or the advent of predation.
However, the advent of molecular clock dating—a technique that estimates the time of evolutionary divergence based on genetic mutation rates—has introduced significant complications to this established narrative. Molecular analyses consistently indicate that the deepest divergences among animal lineages occurred hundreds of millions of years prior to the Cambrian period, deep within the Precambrian. This genetic evidence implies that the evolutionary lineages leading to modern phyla were already well-established long before their first representatives left traces in the fossil record.
To reconcile the stark disparity between the fossil and molecular data, many evolutionary biologists have adopted a revised framework: the "morphological explosion" hypothesis. This model suggests that the Cambrian event was not a sudden burst of lineage origination, but rather a relatively synchronized acquisition of macroscopic size and easily fossilized hard parts—such as shells and exoskeletons—by preexisting, soft-bodied lineages. Under this synthesis, the true evolutionary divergence of animals was gradual and hidden, while the Cambrian explosion represents merely an artifact of taphonomy (the process of fossilization) combined with developmental innovations.
While this synthesis eloquently resolves the chronological tension between fossils and genes, it inadvertently elevates a new explanatory burden. If independent lineages diverged deep in the Precambrian, biologists must now explain the remarkable evolutionary convergence that led these distinct lineages to develop macroscopic forms and hard parts almost simultaneously during the Cambrian. Thus, rather than definitively solving the Cambrian mystery, the synthesis shifts the focus from explaining rapid origination to explaining synchronized morphological innovation.
Which one of the following most accurately describes the logical relationship between the second paragraph and the third paragraph?
- The second paragraph details empirical findings that challenge an established historical interpretation, while the third paragraph presents a theoretical framework designed to reconcile those findings with the original evidence.Cevap
- BThe second paragraph introduces a competing hypothesis to the one outlined initially, while the third paragraph provides the definitive empirical evidence necessary to substantiate that competing hypothesis.
- CThe second paragraph points out a methodological flaw in the traditional interpretation of the fossil record, while the third paragraph proposes a new method of data collection to bypass this flaw.
- DThe second paragraph presents anomalous genetic data that contradicts the fossil record, while the third paragraph argues that this new data must be dismissed due to taphonomic artifacts.
- EThe second paragraph attributes a critical new finding to proponents of molecular dating, while the third paragraph asserts the author's belief that these findings are ultimately misleading.