For example, we know that tetrapods have lost all the bones that protect the gills in fish but that the genes that govern their formation are still present in mice, where they function differently.

• 举例来说，我们知道四足动物失去所有在鱼类用来保护鳃的骨头，但掌管其形成的基因仍存在于小鼠身上，担任不同的功能。