The author is making a point about abstract terms (and thoughts) evolving from earlier, more concrete ones. All he needs of PIE is for it to have preceded english, or more precisely, to have origins from before 2200 BC.
There's pretty clear reconstructions for abstract terms in PIE. And there were certainly copula verbs to indicate existence. PIE was not cavemen grunting. The fact that we can reconstruct it so well from languages spanning two continents indicates it was both stable and well-featured.
I'm not even sure this question means. My previous post is the counter to the book's author's proposal. PIE had abstract vocabulary and several words for existence, including a pure copula "to be", and words such as "to live" and "to grow / become". Furthermore, the fact that we could even reconstruct these words in PIE indicates they were stabilized well before the various child languages began to develop.
If you're trying to make a different proposal, you need to articulate it instead of just being argumentative.
The author is making a point about abstract terms (and thoughts) evolving from earlier, more concrete ones. All he needs of PIE is for it to have preceded english, or more precisely, to have origins from before 2200 BC.