they have all not only lost the pigment in their skin, 它们不仅失去了皮肤色素

254. There may well be less than a hundred Texas cave salamanders in the wild.
     世界上可能只有不到100只 野生洞栖童态河溪螈
255. And the Belizean white crab is another creature that is unique to just one cave system.
     而伯利兹白蟹是另一个 洞穴生态系统中的特有物种
256. Living in perpetual darkness
     由于一直生活在黑暗之中
257. they have all not only lost the pigment in their skin,
     它们不仅失去了皮肤色素
258. but also their eyes.
     眼睛也退化了
259. It takes thousands of generations for eyes to be lost,
     眼睛的退化需要经历数千代的演变
260. so these species must have been isolated for a very long time.
     所以这些物种必定 与世隔绝了相当长的一段时间

来自《行星地球 第一季 第四集 Planet Earth S01E04 洞穴》第 257 行