上面段落摘自CNN一篇文章，请教老师怎样分析文中划线句子的语法结构和中文意思:

The researchers saw changes but nothing that could be related to what's known to be age specific in other organisms.

质疑：学生学过nothing but的用法，文章句子如果改写成The researchers saw nothing but changes that could be related to what's known to be age specific in other organisms.就可以理解成含有定语从句的一个句子。

但面对原文的but nothing结构却感到有些困惑和不解。