Read the passage carefully and answer the six questions.
The Silent Spread
Bioluminescence is the ability of living things to make their own light. This trait evolved on its own more than 40 separate times across nature. Fireflies, deep-sea anglerfish, and certain fungi all glow. But they glow for very different reasons. Scientists once thought glowing was mainly a mating signal. This idea came from fireflies, which flash light patterns to attract partners. But research on deep-sea animals showed a more complicated picture. Anglerfish use glowing lures to attract prey. Some squid release glowing ink to confuse predators. This buys them precious seconds to escape.
This mix of different uses creates a challenge for biologists. Bioluminescence cannot be explained by just one evolutionary pressure. Instead, researchers argue that the light-producing chemical reaction was repeatedly "recruited" by different species. Each species used it to solve a different survival problem: attracting mates, luring prey, or evading danger. The same basic chemistry appears again and again in unrelated organisms. This reaction happens between a molecule called luciferin and oxygen. Its repeated appearance suggests it was a relatively easy trait for evolution to stumble upon and reuse.
Despite decades of study, one mystery remains largely unsolved. Nobody knows why bioluminescence is so much more common in ocean life than on land. Some scientists point to the darkness of the deep sea. They argue this darkness gives any light-based signal a clear advantage. Others note that many land organisms, especially fungi, glow for reasons that still defy explanation.