by studying the 1（水螅） , a member of an ancient group of sea creatures that is still flourishing（繁荣的，盛行的） , scientists at uc santa barbara have made a discovery in understanding the origins of human vision. the finding is published in this week's issue of the 2 of the royal society b, a british journal of biology. hydra are simple animals that, along with jellyfish（水母，海蜇） , belong to the phylum（门） cnidaria（刺细胞动物） . cnidarians first emerged 600 million years ago.
"we 3 which 5 '6,' or ion channel（离子通道） , in the hydra is involved in light sensitivity," said senior author todd h. oakley, assistant professor in ucsb's department of ecology, evolution and 7 biology. "this is the same gateway that is used in human vision."
oakley explained that there are many 8 involved in vision, and that there is an ion channel 4 responsible for starting the 9（神经的） impulse of vision. this gene controls the entrance and exit of ions; i.e., it acts as a gateway.
the gene, called opsin（视蛋白） , is present in vision among vertebrate（脊椎动物的） animals, and is responsible for a different way of seeing than that of animals like flies. the vision of insects emerged later than the visual 10 found in hydra and vertebrate animals.
"this work picks up on earlier studies of the hydra in my lab, and continues to challenge the misunderstanding that evolution represents a ladder-like march of progress, with humans at the 11（尖峰，高峰） ," said oakley. "instead, it 12 how all organisms –– humans included –– are a complex mix of ancient and new characteristics."
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