Question

Read the following dual passages carefully.

Passage A
For decades, the modern evolutionary synthesis has reigned as the undisputed paradigm of biology, resting on a foundational, uncompromising tenet: random genetic mutation is the exclusive source of heritable variation, and natural selection acts upon these permanent DNA sequence alterations. Under this framework, the environment cannot instruct the genome; it can only select from pre-existing genetic diversity. However, the rapidly burgeoning field of epigenetics—the study of structural changes to chromatin that alter gene expression without modifying the underlying DNA sequence—presents a formidable theoretical challenge to this orthodox neo-Darwinian view.

Recent empirical research demonstrates unequivocally that severe environmental stressors can induce specific epigenetic modifications, such as DNA methylation and histone acetylation, which are subsequently passed down intact through multiple successive generations. This transgenerational epigenetic inheritance allows vulnerable populations to adapt to rapid environmental fluctuations far more swiftly than the agonizingly slow accumulation of beneficial genetic mutations would mathematically permit. Consequently, the strictly gene-centric framework of the modern synthesis is increasingly proving inadequate to explain the full spectrum of adaptive phenomena observed in nature. It is becoming abundantly clear that evolutionary biology must undergo a profound conceptual expansion. Rather than completely discarding core Darwinian principles, evolutionary biologists are now compelled to integrate epigenetic inheritance into our overarching evolutionary models, officially recognizing that heritable phenotypic variation is not exclusively dictated by the rigid genetic code.

Passage B
The standard historical narrative of evolutionary biology, which has remained largely unchallenged since the triumphant synthesis of Darwin’s theory of natural selection with Mendelian genetics, posits that evolution occurs exclusively through gradual changes in allele frequencies driven by random, undirected mutation. In this entrenched model, the external environment acts merely as a passive filter, mechanically selecting for advantageous genetic traits while discarding the rest. Yet, the revolutionary discovery that environmentally induced phenotypic characteristics can be directly inherited by offspring without any corresponding modification to the organism's actual DNA sequence demands a critical, urgent reassessment of this conventional narrative.

Epigenetic mechanisms provide a concrete, molecular pathway by which an organism's lifetime experiences—such as severe dietary restriction, psychological stress, or chemical toxin exposure—can directly and predictably influence the developmental phenotype of its descendants. This biological phenomenon effectively resurrects a modified, neo-Lamarckian dimension of acquired inheritance that the architects of the modern synthesis explicitly and forcefully rejected. While some conservative, orthodox evolutionary biologists stubbornly maintain that epigenetic effects are inherently transient and therefore evolutionarily insignificant over geological timescales, this dismissive stance conveniently ignores a mounting mountain of empirical evidence demonstrating stable epigenetic inheritance persisting across numerous generations in wildly diverse taxa. If biological evolution is fundamentally defined as heritable changes in populations over time, then actively excluding a proven, potent mechanism of heritable adaptation simply because it operates outside the traditional genome is fundamentally unscientific. A truly comprehensive, modern understanding of evolution absolutely requires significantly revising the mid-century synthesis to acknowledge that biological adaptation is ultimately driven by a complex, interacting dual inheritance system: one genetic, and the other epigenetic.

Which one of the following most accurately expresses the main point of both passages?