Digital SAT Reading and Writing Practice Question #321

Researchers comparing two divergent lineages of blind cavefish—*species A* found in hydrothermal deep-sea vents and *species B* found in isolated freshwater limestone caves—discovered that both species possess identically stunted ocular structures. Evolutionary models indicate these species diverged over 50 million years ago, making this a striking example of convergent evolution. However, whereas *species B* exhibits a permanent genetic deletion that guarantees ocular degradation regardless of the environment, *species A* retains the complete genetic architecture necessary for fully functional eyes; instead, an epigenetic mechanism actively suppresses photoreceptor development exclusively when ambient water temperatures exceed 40°C. Which conclusion is best supported by the text?