By studying the hydra¹（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 Proceedings² 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 determined³ which genetic⁵ 'gateway⁶,' 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 Marine⁷ Biology. "This is the same gateway that is used in human vision."

Oakley explained that there are many genes⁸ involved in vision, and that there is an ion channel gene⁴ responsible for starting the neural⁹（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 machinery¹⁰ 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 pinnacle¹¹（尖峰，高峰） ," said Oakley. "Instead, it illustrates¹² how all organisms –– humans included –– are a complex mix of ancient and new characteristics."