Only within the monent of time represented by the present ce

这是个倒装句。本来的主干是 one speicies --- man --- has aquired significant power to alter the nature of his world。由于 only 至于句首,而且状语这么长,即 Only within the monent of time represented by the present century,所以 助动词 has 移到到主语前面,这就有了现在这样的结构。