Passage A
For decades, the Modern Synthesis has stood as the unshakeable foundation of evolutionary biology, positing that random genetic mutations, sifted by natural selection, are the exclusive drivers of adaptive evolution. Recently, however, a vocal contingent of biologists has championed "transgenerational epigenetic inheritance"—the passing down of environmentally induced molecular modifications—as a revolutionary addition to evolutionary theory. This enthusiasm is largely misplaced. While it is true that epigenetic marks, such as DNA methylation and histone modification, can alter gene expression in response to environmental stressors, these modifications are inherently unstable. In the vast majority of taxa, epigenetic marks are systematically erased and reprogrammed during gametogenesis and early embryogenesis to ensure cellular totipotency. The rare epigenetic variations that do survive across a few generations lack the durable fidelity required to fuel long-term evolutionary change. Ultimately, the capacity of an organism to mount an epigenetic response is itself a trait explicitly encoded by the underlying genome. Therefore, epigenetic phenomena do not constitute an independent evolutionary mechanism; rather, they represent a form of complex phenotypic plasticity—a regulatory mechanism entirely subsumed under the traditional genetic paradigm. To elevate these ephemeral regulatory fluctuations to the status of a parallel inheritance system fundamentally misrepresents the hierarchical dominance of the DNA sequence in determining evolutionary fitness.
Passage B
The rigid adherence to a strictly genetic view of inheritance has blinded many evolutionary biologists to the dynamic, multi-tiered nature of adaptation. While the DNA sequence undoubtedly provides a crucial informational template, recent discoveries regarding epigenetic inheritance demand a fundamental expansion of our evolutionary models. Organisms frequently encounter rapid, severe environmental shifts that vastly outpace the slow, fortuitous accumulation of beneficial genetic mutations. In these crisis periods, transgenerational epigenetic inheritance acts as an essential evolutionary "first responder," allowing populations to transmit acquired, stress-induced adaptive states to their offspring almost immediately. Detractors often dismiss these epigenetic marks as too transient to matter, pointing to widespread epigenetic reprogramming events in early development. However, this dismissive stance ignores the ecological reality that epigenetic states only need to persist as long as the precipitating environmental stressor remains. Furthermore, these supposedly "transient" epigenetic adaptations can facilitate a population's survival long enough for subsequent, more permanent genetic mutations to arise and assimilate the trait into the hardwired genome—a process known as genetic accommodation. By bridging the perilous gap between sudden ecological change and slow genetic adaptation, epigenetics proves itself to be a primary engine of evolutionary innovation rather than a subordinate mechanism.
Based on the passages, how would the author of Passage A most likely respond to the assertion in Passage B that epigenetic adaptations can "facilitate a population's survival long enough for subsequent, more permanent genetic mutations to arise and assimilate the trait"?
- They would argue that the population's ability to survive the initial environmental shift via epigenetic adaptation is entirely attributable to regulatory capacities already hardwired into their DNA.Cevap
- BThey would reject the scenario entirely on the grounds that epigenetic marks are always completely erased during embryogenesis, making any transgenerational survival advantage impossible.
- CThey would dismiss the process of genetic accommodation as merely a form of complex phenotypic plasticity that lacks the fidelity to alter gene expression.
- DThey would agree that epigenetic states act as an autonomous first responder but maintain that the subsequent mutations must still be sifted by natural selection.
- EThey would counter that the rapid environmental shifts described by the opposing view actually prevent the fortuitous accumulation of beneficial genetic mutations altogether.