The book charts the "behaviour" of what scientists call a gene, how it might have developed, and why certain "behaviours" that living things exhibit (e.g. altruism and agression) can be boiled down to "stimulation from genes."
I don't doubt the science behind the book, I'm not some sort of religious "Flat Earther" who doesn't buy evolution, but after reading the book, I doubt that anyone who's read the book can argue with the idea that any human behaviour can be explained in terms of "genetic behaviour," and to me, that's depressing.