Zoology: The lights that save

Marine biologists have wondered for years why fish and other creatures that live at middling ocean depths carry rows of little searchlights on their bellies. The searchlights (photophores) are cup-shaped organs that are lined with highly reflective tissue and contain luminous cells whose light is concentrated into a downward-pointing beam. Biologists reason that since photophores evolved independently in fish (vertebrates), shrimps (crustaceans), and squids (mollusks), they must have important survival value. But what was it? The bright beams of the photophores shining downward would seem to be a disadvantage, serving only to draw the attention of predators.

In Britain's Nature, William...

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