Primitive life is very common and intelligent life is fairly rare. Some would say it has yet to occur on Earth.

Primitive life is very common and intelligent life is fairly rare. Some would say it has yet to occur on Earth.

原始生命非常普遍，而智慧生命则相当罕见。有些人会说，它还没有发生在地球上。

-- Stephen Hawking 斯蒂芬霍金