The main premise - that our warlike passions stem from our ancient fear of being the prey of the larger and stronger predators that roamed the plains together with prehistoric man - is certainly intriguing. There is plenty of anecdotal support for the possibility both from ancient literature and more modern sociological writing that Ehrenreich brings to bear when developing the theme.
It is hardly a scientific treatise, as it does not compare the theory developed to alternative ones, so one can find it intuitively appealing and like it but it will remain difficult to make an informed choice on whether the theory offers better explanatory power than alternatives, unless you are already an expert in the field. For that part alone, the book deserves 4 stars in my opinion, as it is at least interesting, and it brings some fresh perspectives (and interesting historical trivia) to bear.
Where the book starts unravelling in my opinion is the second part, which purports to apply the prey theory to war. Anyone reasonably familiar with existing explanations of human predatory instincts as well as the difficulties most people have in killing (unless operatively conditioned to do so), will have an extremely hard time swallowing the generalizations and extremely selective view the author presents. Introducing Dawkins' 'Memetics' a handful of pages before the end also does the book no favours, as it seems more of an afterthought than a fully developed explanatory route. On top, I found the weaving in of the theory from the first part often not particularly natural - as if the author wrote two separate books and then found herself encouraged to bind the two together.
Overall this is the weakest of Ehrenreich's books I have read so far. She certainly invested significant effort into writing it but it falls just short of good due to the poor (and partially ideologically motivated, rather than properly analyzed) second half. If the topic is of general interest, you would do well to go through the first part of the book, in case you want to explore the theory developed further - the author's own application is in my opinion not great.
On the other hand, do not judge the author by this book, as her later work, where she experienced the topics she wrote about first hand, is actually quite good.