On the surface this is another self-help book. You can find a summary posted at this link. It contains the standard advice such as “get more sleep”, “eat better”, “exercise” “practice mindfulness” “stay away from negative people and thoughts” “eat more meat”. The book indicates that by following this advice the reader will unleash their inner animal spirit.
The book encourages human beings, the readers, to enter the mindset of a gorilla. As a modern approach, it inverts what was before the goal of political philosophy to encourage human beings to transcend their animal nature on the journey to become a Man or even a Citizen. An individual was not fully human unless they participated rationally in the public domain. When there is reference to man as a social animal or a political animal, it is understood that the animal nature was lower than the human nature. The community’s goal was to develop a man’s character by inculcating virtue for it was his character not his nature that defined him. In turn this man or citizen would contribute to the common good.
With the Enlightenment, we see a change as social contract theorists like Hobbes, Locke and Rousseau suggest that the modern state or society emerges from a pre-political state, a state of nature, where man lives an incomplete life. Hobbes argued famously that life in the state of nature was “nasty, brutish, short, poor, and solitary.” To escape this man creates a commonwealth for a safe, prosperous, and social life. What matters less is character and what matters more is the institutions that contain or shape man. Institutions do not require virtuous member to thrive and the common good becomes an institutional good.
What does all of this have to do with a self-help book?
What we find with this book is that the focus is less on the reader as a citizen or even a man for the focus is on the animal nature of human beings. To improve our lives, the author suggests that we celebrate our instincts so there is little talk of virtue, reason, or the common good. Our minds or our soul become secondary to our instincts. We see no idea that our spiritual life is as important, if not more important, than our physical life. Yet, the gorilla can be appealing for it provides a rudimentary structure to think about life instinctually and not communally.
In gorilla troops, the strong rule the weak. Such a view is antithetical to cultured human society where the idea of justice, a form of political or legal equality, guides public life. Without political equality, or justice, human society starts to decay into brutality (Nazi society, Khmer Rouge society, Maoist society) where one group permanently rules all others. The American experiment was a way to avoid that fate by the focus on reason and what is highest in man. In an America that has lost faith in that experiment, where virtue and character matter less than instinct, the book appears to sell well.
 What is curious is that Gorillas are considered herbivorous not carnivores.