But a group is no organism physically added to its constituent individuals; it has no brain or stomach of its own; it must think or feel with the brains or nerves of its members. 但是，群体除了是由单个的人组成外，并不是真正具有生理作用的有机体，它没有自己的大脑和肠胃；它必须依靠其成员的大脑和神经，进行思考与感知

看了翻译对于这个词语和句子还是没法很好把握，请问这里的add to到底什么意思呢