下句中的the lack of it 充当什么成分

我的观点是呢,是这个句子很简单,没有什么稀奇的.看我调整一下单词的位置和句中标点符号,楼主就会明白了.
And so I started talking to vets,animal researchers,zoo keepers.Most do not study animal intelligence,but they encounter it,and the lack of it,every day.等于就是And so I started talking to vets,animal researchers,zoo keepers.Most do not study animal intelligence and the lack of it but they encounter it every day.
翻译：于是我开始和兽医、动物研究员、动物园饲养/看守员交谈（这个事情）.他们大多不研究动物智能和动物是否缺少智能,然而,他们每天却在与之（指动物智能）打交道.