The thesis of the book is that the genes play as important a role, if not more important, in determining our politics (i.e. party affiliation, ideology, etc.) as does our upbringing, social interactions, education, etc. - the environment, generally speaking. The underlying presumption here is that in mature democracies there develops an ideological coherence, where people unite behind common political principles and goals, and share common beliefs and stances on political and social issues. It is the thesis of the book that this unity is largely the result of shared genetic traits of individuals in a society.
The author doesn't introduce any original research of his own. Rather the thesis is based on synthesis of many research studies spanning several decades and crossing multiple disciplines. While the subject is very interesting, it could have been more effectively synthesized and presented, especially considering that the book is aimed at mass readership. To be sure, there are anecdotes here and there, personal stories and short narratives that accompany research studies. And although the writing style is straight-forward and clear, the content is largely dry. Make no mistake - this is a political science work, with contributions from multiple other disciplines and therefore is not a summer reading material.
With respect to the content, the chunk of the book is persuasive. However, I found some of the inferences to be a stretch, and some works cited seemed cherry-picked to reinforce the author's thesis.
There are many interesting, captivating and even counter intuitive findings. For example, in one British research study, the participants were asked to self-identify their political affiliations and then submit to a MRI brain scan. Based only on MRI of the participants' brains, the researchers were able with 80% accuracy to predict the political affiliation of the participants. The reason is because political conservatives and liberals have different brain structures identifiable in MRI brain scans; moreover, the size and shape of these structures are likely the result of genes rather than the environment. There are many twin studies cited, most of which show that when identical twins are separated and raised in different environments and households, their politics remain largely the same.
Another interesting finding is that southern cultures tend to be somewhat more conservative than northern cultures, across the world. But the counter intuitive conclusion is that it's not that the climate makes people more liberal or conservative, but rather people's climate preferences correlate to their politics and the migration and settlement patterns reflect that. That is, people with liberal genetic leanings tend to prefer northern climates, and those with conservative genetic leanings prefer the southern climates.
The book is full of these kinds of studies and findings, as it tries to isolate the factors that contribute to our politics. And while the book seems solid on most points, some inferences seem far fetched. For example, the author cites Daniel Goldhagen's book, "Hitler's Willing Executioners", in order to demonstrate that the German society was predisposed to anti-Semitism prior to Hitler's ascension. This citation is to support the proposition that the Germanic society had a genetic predisposition toward anti-Semitism. The problem with Goldhagen's book (and thesis) however, is that it has been roundly refuted and discredited by most of the top and mainstream scholars in the field. Therefore, if the Germanic society was not in fact predisposed toward anti-Semitism (at least not more so than other societies), then the argument that it is rooted in genes collapses.
Essentially, when it comes to social issues, conservatives and liberals are vastly different and the difference can be explained substantially on the basis of different gene sets of conservatives and liberals. However, on economics, there is virtually no correlation between how one's beliefs with respect to economics and one's political party affiliation. Thus, in the US exit polls and other studies show that people don't necessarily vote based on their income or other financial interests, but rather on how they feel about the various social issues.
The major problem with the book, aside from some of its far fetched assertions, is that the author doesn't do a good job of pulling all of the disparate sources together to produce a readable and persuasive narrative. Much of the book feels like a set of disjointed summaries of research studies, organized by chapters and sub-chapters. Since this book crosses many different disciplines, it's important to keep an eye on the big picture and not lose the forest for the trees. But in order to understand how all of the parts fit together requires for an author to synthesize the disparate sources and data and relate them to each other in a way that is comprehensive. The author did a mediocre job handling this task.
Despite its shortcomings, much of the book is still interesting and in parts even compelling, even if it's not the final word on the subject - which it surely is not.