Neanderthal and Denisovan retroviruses in modern humans

distribution of the surrounding downwelling light. Deep-sea fishes that have instead evolved to detect bioluminescent point sources have eyes constructed accordingly, typically having a high spatial resolution provided by a retinal area of tightly packed visual cells arranged in a deep pit-like fovea. Their eyes, though, are often quite small, with pupils only as large as necessary to detect points of light at ecologically meaningful distances, which in the nutritionally impoverished deep may only be a few body lengths.