求解长难句教程里的一个例子

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Granted that the presence of these elements need not agure an authorial awareness of novelistic construction comparable to that of Henry James, their presence does encourage attempts to unify the novel's heterogenous parts.

这个句子让步成分的谓语动词need为什么是原型？ 主语不是the presence of these elements吗， 为什么有的解释说主语是elements? 我觉得这两个句子的主语都是presence,主句的动词就是单三,  为什么啊？