这个句子not merely连接了两个从句吗？

They would try to decide what intelligence in humans is really for,not merely how much of it there is. 这里not merely是连接并列的两个从句吗，若是的话为何 not merely可以作连接词呢，它不是副词吗?

They would try to decide what intelligence in humans is really for, not merely how much of it there is.
这个句子的结构，其实 not 权当连词。not 和 merely 没关系，merely 可以不需要。并不是合在一块构成并列连词。网友的句子跟下句是一样的结构：
I want to see her, not you.
不同是：网友句子的宾语都是从句，而这个例句的宾语是代词。

我也举个从句作宾语的例子：

I want to know how you did it, not what you did.