예전에는 사람들이 인간의 눈과 똑같은 시각 색소를 가진 생명체는 지구 상에 한두 개 정도 밖에 없으리라고 생각했습니다.
For example, it was thought that the visual pigments that are in our eyes -- there was only one or two organisms in the environment that had these same pigments.