Final answer:
Lungs in lungfishes evolved from structures similar to the swim bladder, in response to environmental pressures like low oxygen levels in water. Enhanced lung capacity offered a survival advantage in fluctuating habitats, aiding natural selection. Lobe-finned fishes, ancestors to amphibians, had made similar adaptations for life on land.Hence, the correct answer is option A.
Step-by-step explanation:
The evolution of lungs in lungfishes is a fascinating subject that combines several aspects of evolutionary biology. The anatomical precursor to lungs in these fishes is believed to be a structure akin to the swim bladder, which is a gas-filled organ used by many bony fishes to control their buoyancy. Over time, this structure adapted for a new function, transitioning into an organ capable of aerial respiration.
Environmental selective pressures including fluctuating water levels, oxygen-poor water, and periods of drought exerted significant evolutionary stress on fishes. These conditions favored lungfishes that could utilize both water and air for respiration, allowing them to survive when aquatic oxygen levels were too low for gill-breathing alone. Over generations, fishes with enhanced lung capacity had a survival advantage, ultimately leading to the natural selection of lungfishes with lungs suited for breathing air, in addition to their conventional gills.
Such environmental challenges were also instrumental in the transition from aquatic life to land. As ancestral fishes like lobe-finned fishes began to spend more time on land, their appendages and respiratory systems evolved to meet the new challenges of terrestrial locomotion and oxygen intake. These adaptations were critical for the eventual emergence of amphibians and other terrestrial vertebrates.